Tec DeepDigital

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TEC 40

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Tec Deep
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 Tec Deep Diver
Digital Manual

40
Independent
Study
Assignments

Introduction

Chapter 1

Chapter 2

Chapter 3

Handouts

Knowledge
Reviews

Appendix

Main Menu

Tec 40 » Introduction, Chapters One, Two and Three

 Instructor Guide 40 Tec Deep Diver
Digital Manual
Independent
Appendix
Study Assignments
Independent Study Assignments
Please complete assignments as outlined below. Reference the Tec Deep Diver Manual
and Other Study Content, as appropriate. Then complete Tec 40 Knowledge Review One.

Tec 40
Tec 40 Knowledge Development One
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs xi, pg xiii Your Obligations and
Responsibilities, pg xiv Diver Accident Insurance, pg 1-9 including Tec Exercise
1.1. Disregard Tec Deep and Apprentice Tec Diver Certification Limits discussions.
You may skip question 6 in the exercise.
Other Delivery Content, Tec 40-1
Study assignment: Tec 40 Handout 1
Other Delivery Content, Tec 40-2
Study assignment: Tec 40 Handout 2
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 84-87, Oxygen Compatibility
Review, Manufacturer Warranties and Hyperoxic Gases
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 35-50, Gas Planning I,
Tec Exercise 1.3

Other Delivery Content, Tec 40-3

Study assignment: Tec 40 Handout 3
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 51-54, Team Diving I, Tec Exercise 1.4
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 54-59, Techniques and Procedures I,
Tec Exercise 1.5, pgs 107-109, Team Diving Gas Handling Considerations,
Tec Exercise 2.4 questions 4-8, pgs 115-122, Techniques and Procedures III,
Tec Exercise 2.5
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 60-64, Emergency Procedures I,
Tec Exercise 1.6, pgs 123-129, Emergency Procedures II, Tec Exercise 2.6

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Study Assignments
 From

that first moment underwater, I knew that every

spare hour I could squeeze away from mundane duties would

be spent submerged. My greatest regret was that the demands of my

career left too little time for diving.

— Lloyd Bridges
Star of the 1950s television
series, Seahunt.

A
t forty five metres — one hundred fifty feet —
deeper than most recreational scuba divers ever
go — you reach the wreck of a merchant ship
few will ever see. Gloves guard your hands, but you grip
carefully amid the torn, outward splayed sheet metal of
her mortal wound. At your

INTRODUCTION touch, from somewhere

deep in your psyche, you
feel the explosion that
killed this ship. You hear it echo through the decades,
reverberating in the official reports and the black-and-
white films. Past becomes present and history lives as you
feel the steel that once cut the waves in the name of com-
merce.
No book, no picture nor story can do this — only being
there. And that’s when you decide that everything it took
to get you there — the years of experience, the weeks of
training, the hours of planning, the money and the risk
— was worth it.
Twenty five minutes fly by. Time to go. You look to your
team mates, already giving thumbs up. Together you
head up. Above, the surface is far, far away. Your com-
puter tells you that this dive will cost more than hour
in hang time, though you’ll reduce that a bit when you
switch gases at 9 metres/30 feet.
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Tec 40 » Introduction Main Menu Tec 40 Menu Tec 40 Handouts Tec 40 Independent Study Assignments Tec 40 Knowledge Reviews Intro-vii
 This is the type of dive that tec diving — technical deep diving — is
all about. It takes you to sites and experiences beyond recreational
diving, but for a price. Technical deep diving is more hazardous,
and the only way to manage the hazards is through extensive
equipment and the extensive training you need to use it. It requires
you to commit to gaining the prerequisite skills and experience,
to hours practicing and mastering new skills, and then to apply-
ing what you’ve learned strictly, without exception or compromise.
Even then, technical deep diving carries more risk than recreational
diving — and you must be willing to accept this risk.
Technical diving is not for everyone. It is not necessary to be a tec
diver to enjoy diving, nor should you think of it as an inevitable
step in a diver’s growth. You can enjoy diving for decades without
ever making a tec dive. But, if you find you’re interested in it, the
DSAT Tec Deep Diver course is the start, introducing you to the first
step in technical deep diving.
Through the Tec Deep Diver course you’ll learn the rudimentary
skills for diving deeper than 40 metres/130 feet, making dives with
planned staged decompression, and for using multiple gas blends
on a single dive. You’ll find it one of the most intensive and exten-
sive courses you’ve taken; anything less than your full, serious com-
mitment will not be enough. But, if this type of diving appeals to
you, if you’re willing to accept the risks, responsibilities and obliga-
tions, and if you invest the effort and money required, you’ll find it
one of the most rewarding experiences you’ll have in diving.

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 How to Use the DSAT Tec Deep
Diver Manual
The DSAT Tec Deep Diver Manual guides you through the DSAT Tec
Deep Diver and/or Apprentice Tec Diver course (s). You’ll use it as
both your primary knowledge development learning tool for the
course, and a reference you’ll need for planning technical deep dives
long after you finish the course.
During the course, you’ll read each assigned section before meeting
with your instructor to go over and apply what you’re learning. Tec
diving mandates extensive foundational knowledge; it’s crucial that
you complete your study assignments on time as assigned, or
you’ll find it difficult or impossible to progress through the course.
Furthermore, what you study has tremendous bearing on your safe-
ty. This is no place to try to cut corners. It won’t work and you could
get hurt, or worse.
Begin each study assignment by glancing through the chapter and
noting the subheads, topics and pictures. This gives you an idea of
what you’ll be studying and how it fits together, providing the begin-
ning of a mental “framework” upon which to build. Begin reading,
starting with the Tec Objectives as you progress through each section.
Tec Objectives appear as questions that you need to be able to answer;
look for the answers as you read. Underline or highlight these as you
find them — actually writing (not just mentally noting) will help you
when you review for the Exams, plus speeds learning.
You’ll find Tec Exercises throughout each chapter. The Exercises have
two purposes: first, they allow you to gauge your learning. If you have
difficulty with Exercise questions, you can reread the section until you
understand. This avoids trying to move on with incomplete knowl-
edge, which only hinders further learning.
It’s important that you actually write or mark the answers because the
Exercises’ second purpose is to help you transfer what you’re studying
from short term to long term memory. As with actually underlining/
highlighting, writing the answers – not just thinking them – enhances
learning speed and retention.
At the end of each chapter you’ll find a Knowledge Review. Complete
the Knowledge Review, going back to reread material if you have diffi-
culties as necessary. Remove the Knowledge Reviews from the manual
to hand in to your instructor. Your instructor uses the reviews to assure
that you’re studying, to gauge your progress, and to tailor presenta-
tions to the specific learning needs of you and your fellow students.

Introduction ix

Tec 40 » Introduction Main Menu Tec 40 Menu Tec 40 Handouts Tec 40 Independent Study Assignments Tec 40 Knowledge Reviews Intro-ix
 Tec Objectives
Tec Deep Diver and Apprentice Tec
Diver Course Overview
Highlight or underline the The DSAT Tec Deep Diver course consists of six
answers to these questions
as you find them: Knowledge Development sections (including two
exams), eight Practical Applications and twelve
1. What are the goals of
Training Dives sequenced so that you develop new
the Tec Deep Diver and
Apprentice Tec courses? knowledge and skills, building more complex abili-
ties upon prerequisite, foundational abilities. For this
2. What are your obligations
reason, your instructor will require you to successfully
and responsibilities in tak-
ing these courses? complete each Knowledge Development section prior to
the following Practical Application, and each Practical
3. What are the consequenc-
Application before the Training Dives that follow it.
es of failing to meet these
obligations and responsi- (Note: The exception is Training Dive One, which may
bilities? precede its Knowledge Development and Practical
Application.)

Tec Deep Diver Course Goals

The Tec Deep Diver course is the primary course for technical deep div-
ing beyond recreational diving. The DSAT Tec Deep Diver course has five
primary goals:
• To qualify you to make gas switch, extended no decompression dives,
decompression stop dives and accelerated decompression dives using
air, enriched air and oxygen to 50 metres/165 feet, using technical div-
ing equipment and procedures required to manage the risks involved.
• To train you in the motor skills required for technical scuba diving.
• To assure you understand and acknowledge the hazards and risks
involved with the above types of technical diving, as well as the limits
to training received in the course.
• To train you to prepare for and to respond to reasonably foreseeable
emergencies that may occur in this type of technical diving.
• To provide the foundational skills for further training in technical
diving.
Prior to enrolling in the Tec Deep Diver course, you will need to verify
that you meet these prerequisites:
1. Certified as a PADI Advanced Open Water Diver or equivalent.
2. Certified as a PADI Rescue Diver or equivalent.
3. Minimum age: 18 years.

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 Tec Diver Lingo
When you start hanging around with tec divers, kit Your set up gear; scuba unit.
you’ll start hearing terms not common in recre-
long hose The primary second stage on an
ational diving. So, here are a few to get you learn-
approximately 2.2 metre/7 foot
ing the lingo.
hose that you breathe from, and
algorithm Particular version of a decompres- pass to a team mate in an emer-
sion model gency.
back gas The gas in your doubles; usually MOD Maximum Operating Depth —
the lowest oxygen blend you have, the maximum acceptable depth
used on the deepest part of the at which you can breathe a gas
dive. (based on oxygen partial pressure).
With “operating” superfluous,
blow a bag Send up a lift bag.
many divers just use “Maximum
blow up Lose buoyancy control and ascend Depth” interchangeably with
out of control, esp. in a dry suit. “MOD.”
bust a stop Skip a required decompression normoxic gas Air or other gas blend with 21per-
stop, due to error or emergency. cent oxygen.
CNS hit A convulsion caused by oxygen O2 (oh-two) oxygen, or 100% oxygen
toxicity to the central nervous
software Computer software used for creat-
system.
ing custom dive tables.
deco Short for “decompression;” as in
stage To leave something to retrieve
“That calls for six deco stops,”
later, especially a stage bottle or
“That was a short deco,” or “What
decompression cylinder. Sometimes
deco tables are you using?”
used as short for “stage bottle.”
DCI/DCS hit To suffer DCI/DCS.
suicide clip Clip with a swinging gate, such as
gas Generic term for breathing gases, a marine clip, so called because
including any blend of enriched air, they latch to things by themselves,
or air, or oxygen. sometimes posing an entanglement
hazard.
hang Decompression stop or stops, as in
“How long was the hang?” Comes tec, tek, tech Short for “technical” as in “tec div-
from hanging on to an anchor or ing gear” or “she’s a tec diver.”
mooring line while decompressing.
thirds Most common reserve in tec div-
Hogarthian A slang term for the most com- ing — saving one third of gas for
mon, standard tec rig layout. emergencies.
hyperoxic gas A gas blend with more than 21per- tox To suffer oxygen toxicity; often a
cent oxygen. reference to a CNS convulsion.
hypoxic gas A gas blend with less than 21 per- turn pressure Pressure at which you end the dive,
cent oxygen. or turn toward the exit, so that you
end with the required reserve.
jon line Short line used to clip you to the
anchor line while decompressing in wings Tec diving BCD bladders; also
a current. brand name of a BCD.

Introduction xi

Tec 40 » Introduction Main Menu Tec 40 Menu Tec 40 Handouts Tec 40 Independent Study Assignments Tec 40 Knowledge Reviews Intro-xi
 4. Certified as a PADI Enriched Air Diver or equivalent.
5. Certified as a PADI Deep Diver or equivalent.
6. Have a minimum of 100 logged dives, of which at least 20 dives were
made with enriched air nitrox, 25 dives were deeper than 18 metres/
60 feet and at least 15 dives were deeper than 30 metres/100 feet.

Certification as a DSAT Tec Deep Diver means you’re

qualified to plan and make decompression stop dives
and extended no stop dives, using air, enriched air
and oxygen, to a maximum depth of 50 metres/165
feet in conditions comparable to, or better than,
those in which you’ve been trained and have expe-
rience. You’ll also be qualified to purchase or rent
air, enriched air and pure oxygen, and equipment
required for those gas blends.

Apprentice Tec Diver Course Goals

The Apprentice Tec Diver course addresses those div-
ers with a clear interest in and motivation to pursue
tec diving, but who still lack the prerequisite experi-
ence and training required to fully enter tec diving.
The Apprentice Tec Diver course is a subcourse within
the Tec Deep Diver course (first four Knowledge
Certification as a DSAT Tec Deep Diver Development sections, four Practical Applications,
means you’re qualified to plan and make and seven Training Dives) and uses Tec Deep Diver
decompression stop dives and extended
no stop dives, using air, enriched air
course materials, including this manual. The goals of
and oxygen, to a maximum depth of 50 the Apprentice Tec Diver course are:
metres/165 feet in conditions comparable
• To qualify you to make gas switch, extended no
to, or better than, those in which you’ve
been trained and have experience. decompression dives to 40 metres/130 feet using air,
enriched air with up to 60 percent oxygen, using tech-
nical diving equipment and procedures.
• To train you in the motor skills required for technical diving.
• To assure you understand and acknowledge the hazards and risks
involved with technical diving, as well as the limits to the training
received in the course.
• To train you to prepare for and respond to reasonably foreseeable
emergencies that may occur in this type of diving.
• To provide the foundational skills and knowledge for completing the
entire Tec Deep Diver course.

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Tec 40 » Introduction Main Menu Tec 40 Menu Tec 40 Handouts Tec 40 Independent Study Assignments Tec 40 Knowledge Reviews Intro-xii
 Prior to enrolling in the Apprentice Tec Diver course, you need to verify
that you meet these prerequisites:
1. Certified as a PADI Advanced Open Water Diver or equivalent.
2. Minimum age: 18 years.
3. Certified as PADI Enriched Air Diver or equiva-
lent.
4. Certified as a PADI Deep Diver or equivalent.
5. Have a minimum of 50 logged dives, of which at
least 10 dives were made with enriched air nitrox,
12 dives were deeper than 18 metres/60 feet and
at least six dives were deeper than 30 metres/100
feet.
Your instructor may apply the portions of the
Tec Deep Diver course that you complete in the
Apprentice Tec Diver course toward the Tec Deep
Diver course, which you may complete after meeting
all the prerequisites.
Certification as a DSAT Apprentice Tec Diver means
that you’re qualified to plan and make no stop dives
and extended no stop dives using air and enriched
air (up to 60 percent oxygen) to a maximum depth
of 40 metres/130 feet, in conditions comparable to,
or better than those in which you’ve been trained Certification as a DSAT Apprentice Tec Diver
and have experience. You’re also qualified to pur- means that you’re qualified to plan and
make no stop dives and extended no stop
chase or rent air and enriched air (up to 60 percent dives using air and enriched air (up to 60
oxygen) equipment. percent oxygen) to a maximum depth of 40
metres/130 feet, in conditions comparable
to, or better than those in which you’ve
been trained and have experience.
Your Obligations and Responsibilities
Beyond the listed prerequisites, your instructor
accepted you into the Tec Deep Diver or Apprentice Tec Diver course
believing that you have the attitude as well as the aptitude to pursue
technical diving (your instructor has no obligation to accept all students
who apply, even if they meet the prerequisites, provided the basis for
refusal doesn’t go against any antidiscrimination laws, of course). Your
instructor recognizes that tec diving and training for it impose signifi-
cant demands; rising to these challenges begins with you acknowledg-
ing and accepting your responsibilities in this course. You agree to:
• Follow the instructor’s directions and dive plans strictly, and to not
separate from the instructor or your dive team.

Introduction xiii

Tec 40 » Introduction Main Menu Tec 40 Menu Tec 40 Handouts Tec 40 Independent Study Assignments Tec 40 Knowledge Reviews Intro-xiii
 • Refrain from tec diving outside this you discontinue the program. In any case,
course until you’re fully qualified and you will not qualify for certification.
certified.
• Maintain adequate physical and men- Diver Accident Insurance
tal health, and to alert the instructor to Diver accident insurance that covers tec
any problems you have with them. diving, such as the PADI Platinum Diver
• Accept the risk for this type of diving, Protection program (or equivalent), is just
and for specific risks unique to each too inexpensive not to have. Although
dive environment, and to immediately the possibility of a decompression-related
notify the instructor if this risk becomes accident is low, it is still higher than in
intolerable for you. recreational diving. Recompression can
have extensive medical costs that your
Failing to meet these obligations and normal medical insurance may not cover
responsibilities can have unfortunate at all, or not cover entirely.
consequences. In the worst case, you
could be injured, disabled or killed. Even For this reason, having coverage by the
if you avoid these, you will have failed PADI Platinum Diver Protection program,
to demonstrate the attitude and maturity or a similar program, is highly recom-
required for tec diving, and your instruc- mended if it’s available in your area. Your
tor may, in the interests of safety, have instructor may require it.

Tec Exercise – I.1

1. The goals of the Tec Deep Diver course include (check d. providing the foundation for further training in
all that apply): tec diving.
a. qualifying you to make gas switch no decompres-
sion dives. 3. Your obligations and responsibilities as a student in the
b. qualifying you to make decompression dives as Tec Deep Diver or Apprentice Tec Diver course include
deep as 55 metres/180 feet. agreeing to follow the instructor’s ________________
c. assuring you understand the hazards and risks of and _________ __________ strictly, and to not
technical deep diving. _________________ from the instructor or your dive
d. providing the foundation for further training in team.
tec diving. 4. Failure to meet your obligations and responsibilities can
(check all that apply):
2. The goals of the Apprentice Tec Diver course include:
a. lead to injury, disability or death.
a. qualifying you to make gas switch no decompres-
sion dives. b. make it necessary for you to discontinue the
course.
b. qualifying you to make decompression dives as
deep as 50 metres/165 feet. c. make it inappropriate for you to qualify for certifi-
cation.
c. assuring you understand the hazards and risks of
technical deep diving.

Check it out.
1. a, c, d. (b is incorrect — the course qualifies you to 50 metres/165 feet). 2. a, c, d. (b is incorrect — the Apprentice Tec Diver
course does not qualify you to make decompression dives). 3. directions, dive plans, separate 4. a,b,c.

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 ONE
If you can’t take a little bloody nose, maybe you
should go back home and crawl under your bed. It’s not safe
out here. It’s wonderous, with treasures to satiate desires both
subtle and gross. But it’s not for the timid.
— Q, on exploring deep space,
Star Trek - The Next Generation

T
his is a long chapter, though you’ll find it has
the three qualities preferred by students in all
fields the world over: wide margins, large type
and lots of pictures. But the reason for a long
chapter is that technical deep diving requires
that you develop several new, broad sets of knowledge
and skills. Chapter One establishes your learning base
— the fundamentals

Chapter ONE: The Foundation behind everything you’ll

apply and build upon
through all the Knowledge Development sessions, Practical
Applications and Training Dives.
To establish the wide learning base you need for the Tec
Deep Diver and Apprentice Tec Diver courses, Chapter
One plunges you into several topics, most of which you’ll
pick up and further in subsequent chapters. You start by
going over the risks and responsibilities you have as a tec
diver and a member of the technical diving community —
that is, what you’re getting yourself into. Most student div-
ers really love the next topic, tec diving equipment: what
you need, why and how you rig it all together. It’s really
hands on, and you might want to have your gear at hand
while you read.

The Foundation 1

Tec 40 » Chapter One Main Menu Tec 40 Menu Tec 40 Handouts Tec 40 Independent Study Assignments Tec 40 Knowledge Reviews CH1-1
 After that, you’ll get into gas planning,
which is a broad topic that covers what
gases to use, reserves, oxygen toxicity,
dive tables and computers and more. Gas
planning is fundamental to tec diving,
so pay close attention. Team diving shows
you how to work with others for successful
tec diving; think of it as the buddy system
on steroids.
Techniques and procedures gets you back
The Tec Deep Diver Manual establishes the principles into your gear, underwater this time,
you’ll need as you learn, practice and apply tec diving pro- and gives the basics on the skills you’ll
cedures underwater.
be practicing and applying during your
training dives. Emergency procedures does
the same, only specific to handling problems while tec diving. This
leads into thinking like a tec diver, which helps you shape your atti-
tudes and approach to technical diving. This takes you beyond the
how-and-what of tec diving into the mind set that has proved suc-
cessful again and again for the world’s leading tec divers.
Finally, you’ll get an overview of what you’ll be doing as you put
what you learn here into practice during the first practical applica-
tion and training dive.

The Birth of Tec Diving

M
odern technical diving is a relative newcomer It was the publication of aquaCorps magazine that
in diving, largely emerging in the early 1990s brought technical diving “out of the closet” and
as a distinct form of underwater exploration, allowed it to emerge as the distinct, somewhat
but with its origins dating well back to cave diving in extreme activity for a minority of highly visible, but
the 1960s. dedicated divers. Frustrated by mainstream diver
magazines that refused to run articles about the
Tec diving apparently grew out of several diver
pioneers pushing beyond recreational diving limits,
groups who were pushing and exceeding the limits of
writer Michael Menduno founded aquaCorps, simul-
recreational diving. Cave diving had been the main-
taneously coining the term “technical diving.” aqua-
stay of tec diving since the late 1960s, but by the
Corps immediately picked up a following and grew,
mid1980s wreck divers on both sides of the North
soon spawning its associated Tek Conference. Quickly
Atlantic were plunging well past the 40 metre/130
it became evident that there were many small groups
foot limit. Other cave divers – particularly in the 1988
of dedicated divers around the world pioneering
Wakulla Project – were making use of enriched air
technical diving.
nitrox and other gas blends to extend their depths
and durations as they explored farther and farther aquaCorps and the Tek Conference no longer exist,
into underwater caves. All of these groups were qui- but it was through them that tec diving as we know
etly laying the groundwork and establishing new it came to be.
technologies and methodologies.

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Tec 40 » Chapter One Main Menu Tec 40 Menu Tec 40 Handouts Tec 40 Independent Study Assignments Tec 40 Knowledge Reviews CH1-2
 Tec Objectives

ONE
Technical Diving’s Risks and Highlight or underline the
answers to these questions
Responsibilities as you find them:
1. How do you define recre-
Technical and Recreational Diving ational scuba diving and
technical scuba diving?
“What’s technical diving? How does it differ from recre-
ational diving?” 2. What is not technical div-
ing?
If you’re considering getting into it, those are not only
3. What six general risks and
fair questions but ones likely to get different answers
hazards does technical
depending upon who you ask and how confused you diving present that either
want to get. Some people get caught up in whether you’re don’t exist, or aren’t as
diving for fun, or for work, or for what — which only severe, in recreational div-
muddies the issues. If you’re an instructor getting paid, is ing?
it still “recreational”? Maybe that’s commercial or profes- 4. Why does technical div-
sional. Maybe not. See why this approach gets awkward? ing, even done “by the
book,” pose more risk to
We’ll define technical and recreational diving based on you than recreational div-
limits and methodologies and skip whether you do either ing?
for fun, to teach, to make your spouse happy or what- 5. With respect to risk, what
ever. single statement sums up
the difference between
Recreational scuba diving is defined as no stop div-
recreational diving and
ing with air or enriched air to a maximum depth of 40 technical diving?
metres/130 feet, and during penetration dives, within the
6. What are the limits of
natural light zone and no more than a total linear dis-
your training as a DSAT
tance of 40 metres/130 feet from the surface. Typically, Tec Deep Diver or a DSAT
this means using relatively simple equipment (e.g., single Apprentice Tec Diver?
tank and regulator), immediate access to the surface in
7. What risks do you face if
an emergency and less complex training requirements. you exceed the limits of
Thanks to its relative simplicity, it’s open to diverse physi- your training and experi-
cal and mental characteristics, making it an appropriate ence?
activity to a very broad range of people. 8. How could a lack of phys-
Technical scuba diving is diving other than convention- ical fitness affect you as a
technical diver?
al commercial or research diving that takes divers beyond
recreational diving limits. It is further defined as and 9. What are six characteris-
includes one or more of the following: diving beyond 40 tics of a responsible tech-
nical diver?
metres/130 feet, required stage decompression, diving in
an overhead environment beyond 40 linear metres/130 10. What should you do if
feet of the surface, accelerated decompression, and/or the you can’t or won’t accept
the risks and responsibili-
use of variable gas mixtures during the dive. Technical ties demanded by techni-
scuba diving uses extensive methodologies, technolo- cal diving?
gies and training to manage the added risk. Typically

The Foundation 3

Tec 40 » Chapter One Main Menu Tec 40 Menu Tec 40 Handouts Tec 40 Independent Study Assignments Tec 40 Knowledge Reviews CH1-3
 this means using complex equipment in situations
where direct access to the surface is inaccessible due
to a ceiling imposed by decompression, or other
physical barrier such as that found in a cave or a
wreck diving environment. It calls for comparatively
complex and extensive training requirements, with
physical and mental characteristic demands that
limit technical diving to a narrower population. In
technical diving relatively short error chains move
readily to an accident (that is, a single error or only
a couple of linked errors lead to an accident).
Obviously, tec diving has a more open-ended defi-
nition than recreational diving, meaning that you
can classify many different types of diving as tech-
nical diving. However, simply exceeding recreation-
al limits is not tec diving. A diver can’t justify going
to 50 metres/165 feet in the identical kit a recre-
Technical divers (left) compared to recre-
ational diver uses at 18 metres/60 feet by calling it
ational divers (right) use more extensive
technologies and methodologies to man- technical diving. The only thing you call it is stupid.
age the added risk of exceeding recre-
ational limits.

Technical Diving Hazards

Already you’ve read several times that tec diving is more hazard-
ous than recreational diving. Tec diving is rewarding, and presents
challenges and opportunities few other activities offer, but it’s not
without risks. Many tec diving risks either don’t exist in recreation-
al diving, or are more severe than in recreational diving. These
include, but aren’t limited to:
1. Lack of direct or immediate access to the surface in an emergen-
cy due to decompression requirements, distance or both.
2. Hypoxia or hyperoxia, both of which can lead to unresponsive-
ness and drowning. Hypoxia or hyperoxia can result from switch-
ing to the wrong gas, improper gas choice, or failing to properly
analyze your gas.
3. Narcosis, which can lead to poor judgment or bad decisions that
cause an accident, or slowed responses to emergencies that cause
you to fail to adequately handle an accident.
4. DCS with severe permanent injury, or death. This can result
from higher nitrogen/inert gas loading, improper gas analysis, loss
of decompression gas, being forced to surface without completing
decompression, improper decompression calculation, personal pre-

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 disposing factors, diving outside the envelope
of well documented decompression theory, and

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other causes.
5. Omitted procedures and errors caused by
task overloading, leading to accidents from
DCS, gas loss, runaway ascents leading to arte-
rial gas embolism, or barotrauma or oxygen
toxicity caused by runaway descents, etc. The
need for extensive redundant equipment con-
figurations also contributes to task loading due
to ergonomic complexity and physical burden.
6. Drowning due to failed BCD and back
up buoyancy control while diving heavily
weighted with equipment. It is also possible to
drown in heavy gear due to entering the water
with all your cylinder valves closed (due to an
improper predive check) and sink, unable to
inflate your BCD or breathe.
Tec diving has several risks that you don’t
Most of what you learn in the Tec Deep Diver have in recreational diving, including a lack
and Apprentice Tec Diver courses deals with of direct or immediate access to the surface in
an emergency, due to decompression require-
avoiding problems and with what to do if they ments, distance or both.
occur. Still, even when you do everything “by
the book,” tec diving poses more risk than rec-
reational diving because there are more variables, more potential
hazards, the error chain leading to an accident is short, and surfac-
ing in an emergency is (usually) not an option.
To compare recreational diving to technical diving: In recreational
diving, when you do everything properly to the best of your ability,
the probability of a serious accident is very remote. In technical div-
ing, with short error chains and surfacing generally not an option,
this isn’t true.
In fact, you can sum up the difference between recreational and
technical diving in this statement: In technical diving, even if you do
everything right, there is still a higher inherent potential for an accident
leading to permanent injury and death. You must accept this risk
when you enter into technical diving and technical diver train-
ing.
But let’s not be overly dramatic. The vast majority of tec diving
accidents result, as in recreational diving, from failing to apply the
proper procedures, failing to have the required equipment, or fail-
ing to have the prerequisite training and/or experience. So, if you
stay within the limits of your equipment and training, and you fol-

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 low the proper procedures you learn, the probability of an accident
isn’t high — but it is there, and higher than in recreational diving.
And, as stated before, if you have
an accident, the consequences may
be worse than a similar accident in
recreational diving.
Let’s look at the training limits
of the DSAT Tec Deep Diver and
Apprentice Tec Diver certifications.
Tec Deep Diver Certification
Limits. As a certified DSAT Tec
Deep Diver, you’ll be qualified to:
• Dive to a maximum depth of You can sum up the difference between recreational and
50 metres/165 feet using air or technical diving in this statement: In technical diving, even
enriched air. if you do everything right, there is still a higher inherent
potential for an accident leading to permanent injury and
• Make decompression dives using death. You must accept this risk when you enter into tech-
nical diving and technical diver training.
air, enriched air or oxygen.
• Make extended no stop dives by switching gases during the dive.
Apprentice Tec Diver Certification Limits. As a certified DSAT
Apprentice Tec Diver, you’ll be qualified to:
• Dive to a maximum depth of 40 metres/130 feet using air or
enriched air (max 60 percent oxygen).
• Make extended no stop dives by switching gases during the dive.
In both cases, the limits are based on using the required equip-
ment and following the procedures you learn in this course, and
on allowing for your experience or inexperience in the particular
environment.
Risks from Exceeding Your Limits. Exceeding the limits of your
training and experience poses some severe risks. Bluntly, you can
suffer permanent injury, or death, due to an accident. Accidents
caused by diving beyond limits usually arise because a) the diver
fails to recognize a hazard, b) the diver doesn’t know the procedure
for preventing or handling a hazard or emergency, or c) the diver
knows the procedure, but due to lack of practice either can’t exe-
cute it, or executes it improperly.
Most divers who’ve had accidents when diving beyond their limits
believed they knew how to handle the situation. Unfortunately,
they were wrong. Some paid with their lives for this mistake.
Physical Fitness and Tec Diving. Hand in hand with your train-

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 ing and experience limits, you need to consider your physical limi-
tations. Tec diving imposes higher physical demands on the diver

ONE
than does recreational diving, particularly before and after the
dive. These demands include wearing, standing in, boarding lad-
ders or moving in substantially heavier gear. In hot weather, you
may be exerting with this load while wearing a full dry suit or wet
suit, imposing a high thermal stress. In the water, your gear adds
significantly more drag, requiring more strength to speed up in an
emergency, and more strength and endurance for a long swim. A
long decompression, even in moderate water temperature with full
exposure protection, can impose thermal stress due to chilling.
Physical fitness affects your performance and abil-
ity as a tec diver. Just as in recreational diving,
you need to be confident that you have adequate
physical resources for the dive you plan, plus suf-
ficient reserve to deal with emergencies. Most tec
dives call for higher fitness requirements than
recreational dives. Lack of the physical fitness
required can affect your safety by limiting your
ability to respond to an emergency, or by directly
leading to injuries such as a heart attack, heat
exhaustion or stroke, broken bones or muscle tears
due to falling or strain.
Consider that your cardiovascular system needs
to be able to tolerate thermal stress, plus support
the muscle demand for oxygen while wearing
and moving in heavy equipment out of water
and while swimming at a moderate pace against
Physical fitness affects your performance and
the drag. You need sufficient skeletal and bone ability as a tec diver. Lack of the physical fit-
strength to carry the equipment — while wearing ness required can affect your safety by limit-
it and while loading, unloading and transporting ing your ability to respond to an emergency,
or by directly leading to injuries. You need
it to and from the dive site. Only you and your sufficient skeletal and bone strength to carry
physician can determine your fitness and assess the equipment – while wearing it and while
its suitability for different types of diving. It’s your loading, unloading and transporting it to
and from the dive site. It’s your responsibil-
responsibility to stay fit to dive, and to dive within ity to stay fit to dive, and to dive within the
the limits of your fitness. limits of your fitness.

The Responsible Tec Diver

The need to address the risks and hazards of tec diving has resulted
in a philosophy reflected in the way the world’s leading tec divers
think and behave. (You’ll be learning a bit more about this in the
Thinking Like a Technical Diver sections of each chapter.) Despite

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 tremendous cultural and personality differences, six characteristics
seem to universally denote the responsible technical diver. As you
go through the course, these are characteristics you want to learn,
and adopt.
Self Sufficient. The responsible tec diver plans and
executes each dive as though it’ll be necessary to
make the dive and handle all emergencies alone.
That is, you should never rely on any other diver for
the safety or knowledge required to execute a dive.
Team Player. Although self sufficient, the respon-
sible tec diver dives as part of a team (not simply
a buddy — more about this shortly). When you tec
dive, you need to think of yourself as a team player
contributing to a team effort.
Disciplined. Technical diving has too little leeway
for cutting corners, bending rules, disregarding dive
plans, omitting safety equipment or exceeding the
limits of your training and equipment. Responsible
tec divers maintain their self discipline, and so
should you.

Technical diving has too little leeway for Wary. One of the best ways to come back from every
cutting corners, bending rules, disregard- technical dive is to assume that everything can and
ing dive plans, omitting safety equipment will go wrong, and then have contingency plans for
or exceeding the limits of your training
and equipment. Responsible tec divers are when it does. Responsible tec divers are just a tad
methodical and uncompromising in every- paranoid, and it serves them well.
thing from predive checks to post dive
debriefings. Physically Fit. Responsible technical divers exercise
regularly, eat properly, see their physician regularly
and maintain the fitness level they need for the dives they make.
You don’t have to be an Olympian, but you do need to be fit for the
dives you make, and as you just learned, that includes having suf-
ficient physical reserve for emergencies.
Accepts Responsibility. To be a responsible technical diver, you
need to accept responsibility for your personal safety, while accept-
ing and acknowledging the risks and demands tec diving imposes.

If You Won’t, Don’t

After reading this section on technical diving’s risks and respon-
sibilities, you might think this manual’s trying to talk you out of
becoming a technical diver.
You bet!

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 The fact is, you can enjoy a lifetime of exciting, adventurous diving
without ever making a decompression dive, without ever ventur-

ONE
ing deeper than 40 metres/130 feet and without ever penetrating a
wreck or cave farther than that. Technical diving is not for every-
one and it is not a goal for all divers to aspire to.
Therefore, if you can’t or won’t accept the responsibilities, risks and
demands required by technical diving, then don’t do it. All you’d be
doing is endangering yourself and your fellow divers. Stop now. If
you will accept them, on the other hand, then you’re ready for the
next step in your training.

Tec Exercise – 1.1

1. You define “technical diving” as diving beyond 5. In technical diving, even if you do everything
_____________ ____________ limits. It includes decom- __________, there is still a higher inherent potential
pression stop diving and overhead environments, for an ____________ leading to ___________ ________
using __________________ ______________________ , and ________.
___________________ and ______________ to manage 6. Certified Apprentice Tec Divers are qualified to make
the _____________ ____________. no stop dives with no stop time extended by switch-
ing gases during the dive.
2. Some forms of technical diving include making very
deep (below 40 metres/130 feet), short dives using True False
equipment no different from what you would use on
a typical recreational dive. 7. Exceeding the limits of your experience and train-
True False ing in tec diving risks ______________ __________ or
______________.
3. General risks and hazards in tec diving that either
don’t exist or aren’t as severe in recreational diving 8. Lack of the physical fitness required for a dive can
include (check all that apply): affect your ____________ by limiting your ability to
a. lack of direct/immediate access to surface respond to a(n) _________________, or by directly
b. exposure to marine predators leading to ___________.
c. DCS 9. Characteristics of a responsible technical diver include
d. drowning due to failed BCD while diving heavily (check all that apply):
weighted with gear a. self sufficient c. wary
b. disciplined d. accepts responsibility
4. Even when you do everything right, technical diving
has more risk because there are more ____________ , 10. If you can’t or won’t accept the risks and responsibili-
more potential _____________ , the ______________ ties of technical diving then _______ ______ _______.
___________ leading to an accident is short, and
___________ in an emergency is usually not an option.

Check it out:
1. recreational diving, extensive methodologies, technologies, training, added risk. 2. False. Tec diving employs more extensive
equipment to manage risks. 3. a, c, d. b is incorrect because technical diving doesn’t cause a substantial increased risk from
marine animals. 4. variables, hazards, error chain, surfacing. 5. right, accident, permanent injury, death. 6. True. 7. perma-
nent injury, death. 8. safety, emergency, injury. 9. a,b,c,d. 10. don’t do it.

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 Equipment I – The Basic Technical Diving Rig
Scuba diving’s a gear-intensive activity, but tec diving redefines
“gear-intensive.” In the diving world, snorkelers are gazelles, recre-
ational divers are horses and techni-
cal divers are elephants. Tec diving
requires a substantial investment in
dive gear, but most tec divers have
at least a bit of technophile in them,
making the equipment part of the
appeal.
In recreational diving, you enjoy
a good bit of latitude in how you
arrange your gear. The demands
of technical diving and working in
teams, on the other hand, impose a
Scuba diving’s a gear-intensive activity, but tec diving rede-
fines “gear-intensive.” In the diving world, snorkelers are
need for higher standardization. For
gazelles, recreational divers are horses and technical divers are this reason, the rig you’re about to
elephants. learn has evolved in the technical

Tec Objectives
Highlight or underline the answers to these questions as you find them:

1. What is meant by “standardized technical rig,” 8. What instrumentation do technical divers generally
and why do technical divers need to apply it? carry, and why do they generally avoid consoles?
2. What guidelines apply to selecting masks, fins and 9. What are the three types of computers you can
snorkels for technical diving? use for technical deep diving with air and enriched
air, and what are the advantages and disadvan-
3. What characteristics should you look for in a cylin-
tages of each?
der valve or manifold used for deep technical
diving? 10. What types of cutting tools are appropriate for
deep technical diving, and at least how many
4. What is the minimum number of fully independent
should you have with you?
regulators, per diver, and how do you configure
each? 11. What are six general guidelines regarding pockets,
accessories and clips you might need when techni-
5. What three characteristics should you look for in a
cal diving?
BCD, and what five characteristics should you look
for in a harness, for a deep technical diving rig? 12. What are four recommendations regarding equip-
ment maintenance?
6. How do you choose an appropriate exposure
suit for a deep technical dive, and how may your You should also be able to:
choice affect your BCD choice? 13. Describe the layout, arrangement and configura-
tion of the basic rig and equipment, head to toe,
7. What are your options regarding a weight system,
as worn for a technical deep dive.
and what are the advantages and disadvantages of
each?

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 community as the generally accepted basic tec diving setup. You
still have some latitude to individualize your kit, of course — you’re

ONE
not being molded into a robot.
The best way to understand the basic rig is to first cover the phi-
losophy behind it — why it is how it is — and then focus on each
component and how it differs from the same component (if it does)
in recreational diving. Then you’ll look at how they all integrate
into a surprisingly simple package that’s the heart of being a lean,
mean diving machine.

The Standardized Technical Rig

The most widely accepted technical rig springs from a gear lay-
out and philosophy that originated with cave diving and slowly
evolved into the “standard” way of doing things. The reason for the
wide acceptance and emergence of this rigging mode as standard
is because it follows a philosophy of streamlining and minimizing
your gear so that nothing dangles, everything is accessible, and
you eliminate the unnecessary. The current evolution emphasizes a
diver/gear philosophy of “rig wreck, dive cave,” which means you
set your gear up for the most demanding environment (the deep
wreck), but dive with the skill and finesse that typifies
cave diving (efficient, no silt, complete buoyancy con-
trol mastery).
That may sound simple, but given the extensive
equipment requirements of tec diving, it has been one
of the challenges since its emergence. This is more
than a convenience issue — you need to apply the
standard technical rig philosophy to minimize con-
fusion and procedural error due to equipment task
loading. In an emergency, there’s not a lot of time to
figure out where your team mate’s alternate second
stage is. Streamlining is crucial to avoid entangle-
ment and to conserve energy by minimizing drag. The
standardized layout goes a long way to meeting these
requirements.
The standardized technical rig setup you’re about
to learn has become the most widely accepted basic The standardized technical rig setup
tec rig layout for the simple reason that it works. It has become the most widely accepted
basic tec rig layout for the simple rea-
accommodates variations to meet the specific needs
son that it works. It accommodates
you have as an individual and the varying demands variations to meet the specific needs,
of differing environments. It does this, yet maintains yet maintains sufficient standardization
sufficient standardization to minimize routine equip- to minimize task loading.

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 ment handling and use as a major
task load in the trained individual.
Even highly specialized forms of tech-
nical diving, such as sidemount cave
diving (tanks worn on the sides), tend
to originate with the standardized rig.

Mask, Fins and Snorkel

Choose a mask that’s compact to max-
Even highly specialized forms of technical diving, such as imize streamlining and minimize hav-
sidemount cave diving (tanks worn on the sides), tend to ing it jostled by current. It’s also faster
originate with the standardized rig.
to equalize when descending quickly.
Comfort is everything, especially con-
sidering you may be wearing it for two to three hours.
The mask strap should have retainers that
keep the loose ends from dangling off your
temples. Most decent quality scuba masks
will do the job.
For foot power, you need full-size power
fins with sufficient blade area and flex.
Most open heel, full size scuba fins meet the
requirements; small full-foot fins typical of
snorkeling and some tropical recreational
diving won’t cut it.
Again, consider comfort
— after pushing a full
tec kit against a mild
current for two hours, a Choose a mask that’s compact to maximize
minor pinch you put up streamlining and minimize having it jostled
with at the start turns by current. Comfort is everything, especially
considering you may be wearing it for two to
into sheer torture by the
three hours.
end.
Many modern fins have
strap retainers that keep the loose ends from
flopping around. If not, you can often reverse
You need full-size power fins with sufficient them so the loose end routes to the inside (but
blade area and flex, like these two well-worn check that the buckle still holds) or tape the
sets. Many fins have strap retainers that keep
loose ends with duct tape or electrical tape.
the loose ends from flopping around (right). If
not, you can often reverse them so the loose end If you’re one of those divers who finds a snorkel
routes to the inside or tape the loose ends with
duct tape or electrical tape (left). annoying, here’s one thing you’ll love about tec
diving: you almost never wear a snorkel. While

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 they’re important standard equipment for recreational diving, in
most tec diving circumstances they create drag and an entangle-

ONE
ment hazard, with little real benefit.
That being said, it would be wrong to
say that they’re never used in techni-
cal diving. In rare instances with long
waits or swims at the surface in rough
conditions, you might use a snorkel
and then remove it, stashing it in your
rig or leaving it on a float or handing
it up to the boat, etc. So, the snorkel
you have already probably does the
job just fine because, chances are, you
won’t be using it. If you think condi-
tions may call for it, you’ll want a
You almost never wear a snorkel when tec diving. quick release snorkel keeper that lets
While they’re important standard equipment for rec-
reational diving, in most tec diving circumstances they
you detach it easily without removing
create drag and an entanglement hazard, with little your mask.
real benefit.
Full face
masks are not widely used for tec diving
at this writing because they make it diffi-
cult to switch gas rapidly or use your team
mate’s long hose. However, at least one

KMS-48 © 2000 Kirby Morgan

company is manufacturing a model with
interchangable mouth “pods” that permit
the diver to easily change gases and use
standard second stages. The use of such
a mask may be especially beneficial dur-
ing decompression with oxygen because
it may reduce drowning risk in the event
of a convulsion. You may see these more
commonly as they become available, and The KMS-48 full face mask is a model with inter-
they may be the future trend in technical changable mouth “pods” that permit the diver to eas-
ily change gases and use standard second stages.
decompression diving.

Cylinders and Valves

Most of the time, deep tec diving calls for twin cylinders that you
choose based on your individual gas consumption, your size, and
the dive requirements. In some instances a high capacity single cyl-
inder, such as a 18-20 litres/105-120 cubic foot size, will suffice for a
dive that’s not too deep and has only a very short planned decom-
pression, but most of the time you’ll be in doubles. You may use a

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 high capacity single cylinder for some of the training dives in Tec
Deep Diver and Apprentice Tec Diver courses, but you will be using
doubles most of the time, if not all.
Twin cylinders, 11-12 litres/71.2-80 cubic feet
each, are sufficient for many divers going
no deeper than 50 metres/165 feet. Popular
larger cylinders (18-21 litres/105-120 cubic
feet each) are more common for longer
dives, which require more gas on the bottom
and for decompression.
The prime choice for a manifold (doubles
valve) is the DIN (Deutches Industrie Norm)
isolator manifold. This manifold uses the
DIN system instead of the yoke, which is
The prime choice for a manifold is the DIN isolator
manifold. The manifold has twin regulator posts, preferred because the captured o-ring is con-
each of which you can close in the event of a regula- sidered more reliable in the event of impact.
tor malfunction while still providing access to all the The manifold has twin regulator posts, each
gas in both cylinders to the back up regulator. The
isolator valve permits you to separate the cylinders
of which you can close in the event of a reg-
and save half your gas in the event of a manifold leak ulator malfunction (runaway freeflow) while
on one side. still providing access to all the gas in both
cylinders to the back up regulator. The isola-
tor valve permits you to separate the cylinders and save half your
gas in the event of a manifold leak on one side.
In some areas, you may have difficulty find-
ing isolator manifolds, but the twin regulator
posts are considered mandatory equipment; the
old fashioned single valve doubles manifold is
unacceptable for tec diving. Likewise, mounting
two singles in doubles bands isn’t considered
acceptable due to complexity
in gas management, and the
inability for one regulator to
access all the gas in both cyl-
inders. You’ll be using doubles
with an isolator manifold in
this course. The DIN (Deutches Industrie Norm) DIN sys-
tem is preferred because the captured o-ring
If you’re tec diving with a high is considered more reliable than the yoke
capacity single cylinder, choose system in the event of impact.
an “H” or “Y” valve that lets
you mount two separate regu-
lators on a single tank, again with the DIN system
A “Y” valve lets you mount two separate preferred. (Obviously, there’s nothing to isolate
regulators on a single tank.
when using a single cylinder.)

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 Manifold Accessories. The prevailing practice is to keep things
simple, so most of the tec diving community run the manifold as is.

ONE
However, a few areas have specialized needs regarding tank valves.
In the United Kingdom, for example, some wreck divers use guards
to protect the manifold from impact inside of wrecks. Similarly, a
cable for closing the isolator valve by remote has become popular
because the combination of cramped wreck
interiors and dry suits can make reaching the
valve difficult or impossible.
Excepting these regionalized needs, you gener-
ally want to follow the standardized technical
rig layout and methods to avoid clutter around
the valves. You can’t see this area while kitted
up, so keeping it clean and simple is the best
way to avoid problems. Note, for instance, that
you completely remove valve covers and dust
caps (from your regulators, too) rather than
allow them to dangle from strings as do recre-
ational divers.
Doubles Bands. Doubles are set up with steel
bands with their mounting bolts 28 cm/11
inches apart (standardized to fit BCDs and
back plates). You bolt the cylinders to your
BCD and harness together with wing nuts on
the mounting bolts.
Setting up doubles takes some training and
finesse, so it’s something you should leave
to your PADI Dive Center or Resort, unless Setting up doubles takes some training and
finesse, so it’s something you should leave to your
you’re trained and qualified to set them up. PADI Dive Center or Resort, unless you’re trained
Improperly set up doubles don’t lie flat, mak- and qualified to set them up. Improperly set up
ing them awkward to work with, and the lack doubles don’t lie flat, making them awkward to
work with, and the lack of proper alignment can
of proper alignment can make the manifold make the manifold fail, resulting in a runaway
fail, resulting in a runaway leak. leak.

Regulators
In deep tec diving (and most other forms of technical diving), you
should always have two fully independent regulators available.
This doesn’t include regulators you use on your decompression or
stage cylinders. The reason why you want at least two is that you
usually can’t simply surface in an emergency as you can while
recreational diving. Therefore, you need another way to breathe
should one of your regulators malfunction.

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 Choose top of the line balanced regulators for maxi-
mum reliability and performance. Since you’re
ideally using a DIN manifold, you need DIN fitting
regulators (simple adapters allow you to use them
on yoke valves in a pinch.)
You set up the right post regulator (the one on the
right side of the manifold when you’re wearing the
set) with a low pressure inflator hose to your BCD,
and the second stage on a hose about two metres/
seven feet long. You’ll commonly hear this called
simply your “long hose.”
Set up the left post regulator with the SPG and the
second stage on a standard length (about 80 cm/
32 in) hose. A low pressure hose to your back up
BCD and/or your dry suit comes off the left, if appli-
You set up the right post regulator with
a low pressure inflator hose to your BCD,
cable. Otherwise, you have no low pressure inflator
and the second stage on a hose about two hose coming off of it. (More about these options
metres/seven feet long. You set up the left shortly.) Note that there’s only one second stage per
post regulator with the SPG and the second
first stage.
stage on a standard length hose.

BCD and Harness

Your basic technical rig calls for a harness that sandwiches an inter-
changeable BCD bladder against the cylinders, everything
bolted together via recessed wing nuts that screw onto the cylinder
band mounting bolts. Many recreational BCDs don’t meet the needs
of tec diving (D-rings on the shoulders don’t necessarily make a
BCD a tec diving BCD). Although you usually invest in your BCD
and harness as an integrated system, they’re separate components
with differing selection criteria.
BCD. Technical BCDs are sometimes called “wings” because they
let you “fly” doubles and resemble stubby wings protruding from
the tanks behind you. You choose your BCD based on your needs
regarding size, single or double bladder, and unrestrained or bun-
geed design.
Size – You choose your BCD size based on having adequate lift to
hold you at the surface wearing all the gear you need for the dive,
and with all cylinders full. (In tec diving, the difference between
having full and empty cylinders can be 7 kg/15 lbs or more.) You
can choose different sizes based on your need so that you have ade-
quate buoyancy, while not having way more than you need. A BCD
that’s too big just adds drag and can complicate buoyancy control.

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 Single or double bladder – You can
also choose between single bladder

ONE
and double (redundant) bladder BCDs.
A single bladder has a single air cell
and inflator, whereas the double blad-
der has a second air cell and inflator
for back up (not to double your buoy-
ancy — you always use one air cell at
a time).
Whether you need a double bladder
BCD (sometimes called “double wings”)
depends on the dive requirements. You can choose different BCD sizes based on your
need so that you have adequate buoyancy, while
In all cases, you should have back not having way more than you need.
up buoyancy. If, for example, drop-
ping your weights in the event of BCD
failure would still leave you substantially negative, then a double
bladder BCD might be the best way to go. But, you still want the
simplest rig that does the job.
Typically, if you’re in a dry suit
with lighter cylinders, that may
provide adequate back up buoy-
ancy control and a single bladder
can be appropriate. The heaviest
cylinders can weigh too much to
use a dry suit reliably for back up
buoyancy control, or you may be
diving in a wet suit. In those cases,
the double bladder BCD provides
the back up you need. If you dive
You can choose between single bladder and double (redun-
dant) bladder BCDs. A single bladder (right) has a single in several environments, you may
air cell and inflator, whereas the double bladder (left) has a find you need both single and dou-
second air cell and inflator for back up. ble bladder BCDs, using whichever
one fits the circumstances.
Although not commonly seen today, the original “double bladder”
was accomplished by stacking two single bladder BCDs under the
harness plate. This works adequately and is acceptable, but has
fallen out of favor because it adds substantial bulk and drag. Some
divers reduced the bulk by using a slightly smaller BCD for the
back up.
Unrestrained or “bungeed” BCDs – Bungeed wings have elastic or
tubing that constricts the BCD to minimize its profile, while stretch-
ing to expand when you fill the BCD. Bungeed wings are useful in
wreck penetration, for instance, to reduce snag potential, and the

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 constriction squeezes air out of the bladder, making bungeed BCDs
deflate more rapidly than unrestrained BCDs.
However, there’s much made in some
circles about what happens with a hole
or exhaust valve failure using a bungeed
BCD. Unrestrained BCDs will usually
still hold a fair amount of gas (depend-
ing on where the hole is), whereas bun-
geed BCDs tend to squeeze the gas out.
Unrestrained BCDs lie flat against your
cylinders when you’re swimming, so they
produce less water drag. Improperly rigged
bungeed wings may not expand to their
You choose between bungeed BCDs (left) and unre-
full size, leaving you with significantly less
strained BCDs (right). The model on the left is adjust- buoyancy than you thought; this can be
able, and you can easily release the bungee if necessary. hazardous. On the other hand, properly
rigged bungeed wings still usually hold
a good bit of air with a hole or exhaust
valve failure, they expand to their full size when necessary, and
they protrude less in the snagging environment of a wreck.
Again, keep it simple. If you need bungeed wings for a clear
advantage, as in wreck penetration, then use them following the
manufacturer specifications for setting them up. If you don’t need
them, then use an unrestrained BCD. With some, you can remove
and replace the bungee system as needed. Some new, more sophis-
ticated BCD wings offer the advantages of bungeed wings and
unrestrained wings at the same time. With these, you adjust the
bungees for the required buoy-
ancy, and you can release the
bungee system with a single
cut, unrestraining them so
they hold ample air with a
failed exhaust valve or small
puncture.
Harness. Your harness holds
the BCD to the cylinders and
everything on to you, so it
has to be strong and reliable.
Characteristics to consider
include style, crotch strap The plate style harness (left) routes standard nylon webbing
through a shaped back plate. It’s simple, reliable and strong. The
availability, adjustable shoul-
soft harness (right) is made of standard nylon webbing. It does
der quick releases, adjustable the same job, but tends to be a bit more comfortable and versa-
D-rings and waist strap types. tile. By the way, the rigs are on the rail for picture purposes and
secured from the behind.

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 Style – There are two acceptable styles: the plate
and soft harness. The plate style (steel, aluminum

ONE
or plastic) routes standard nylon webbing through
a shaped back plate. It’s simple, reliable and
strong. The soft harness is made of standard nylon
webbing. It does the same job, but tends to be a bit
more comfortable and versatile, plus it’s lightweight
(a bonus for the traveling diver). However, it’s not
quite as simple, though simple enough to meet the
standardized rig philosophy.
Crotch strap – Not an option, but a necessity due to
the bulk and buoyancy distribution of your doubles.
If the harness won’t take a crotch strap, find one
that will. To handle the bulk and buoyan-
cy distribution of doubles, choose
Shoulder harness adjustable quick release connec- a harness with a crotch strap.
tors – Although most common on soft harnesses,
you can get these on plate harnesses as well. They
make it easier to get into and out of your rig, and you can usually
adjust them while diving. Early versions didn’t hold the weight of
tec diving gear well, but that’s not much of an issue today.
They’re not needed for general diving, but convenient. If you opt
for them, put a short piece of bungee or surgical tubing on the bot-
tom of each side to keep the free end of the webbing from dangling.
One instance where they can make an impor-
tant difference is in a rescue situation. It’s
tough getting an unresponsive diver out of a
standard harness — the rescuer may have no
choice but to cut the straps; the quick releases
alleviate this.
Adjustable D-rings at shoulders and waist
– You need at least one, or a maximum of
two D-rings on the harness shoulders, with
the standoff (bent or rigid) D-rings the ideal
Although most common on soft harnesses, you can get because you can more easily get a clip onto
adjustable, quick release buckles on plate harnesses as them. You need a rigid D-ring on the waist
well. They make it easier to get into and out of your strap at the hips, one on each side (these are
rig, and you can usually adjust them while diving.
Note the bungee loop for tucking the free end, which
usually vertical, but you can also get horizon-
reduces “danglies.” tal rigid D-ring systems — either does the job.)
It’s essential that you have D-ring locations
where you need them to carry your stage/decompression tanks
and accessories (more about these later). Therefore, fixed location
D-rings aren’t usually a good choice — with one exception: a few
manufacturers make custom harnesses measured specifically for

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 you, placing the shoulder D-rings exactly where you
need them. This is still “adjustable” in that they’re
adjusted to you, then fixed in place.
If you’re using adjustable quick release
connectors, the shoulder D-rings go
above the connector. You need to do
this so you have unrestricted web-
bing to slide through the connector.
When wearing a stage/deco bottle,
this arrangement also keeps the rig on
you if the connector were to separate
(although that’s highly unlikely with
modern harnesses).
Waist strap – Your harness should have
standard webbing and a buckle as a
waist strap. A removable “cummer-
You need at least one, or a maximum bund” under the webbing is acceptable
of two-D rings on the harness shoul- (most common on soft harnesses), but
ders. They need to be in the right
place, so you want D-rings you can avoid a harness that has only a cum- You need a rigid D-ring on the
adjust. merbund (not as strong and creates waist strap at the hips, one on each
gear positioning problems). Most tec side, for attaching stage/deco cylin-
ders and accessories.
divers remove optional cummerbunds. Many divers
prefer a metal buckle to avoid breakage when mov-
ing heavy gear.
In choosing and setting up your BCD and harness,
keep in mind that the wings may or may not be
partially integrated into the harness. Integration
is fine, provided you can choose the components
described above as needed to fit your requirements.
As mentioned, you may find you want two or three
wings, or entirely separate BCDs and harnesses, to
match differing requirements in differing dive envi-
ronments.

Exposure Suits
As in recreational diving, you choose an exposure
suit for a tec dive based on the water temperature
at depth and the dive duration. When you’re new to If you’re using adjustable quick
tec diving, it’s easy to underestimate your insulation release connectors, the shoulder
D-rings go above the connector.
requirements. What keeps you comfortable for a
short recreational dive usually won’t do it for a long
tec dive.

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 You almost always need a good bit more insulation due to the
duration, and because you spend much of the time making decom-

ONE
pression stops where you don’t exert much and warm up. It’s not
unusual to wear a dry suit in water that recreational divers find
a wet suit more than adequate for, or to wear a full wet suit with
hood when the recreational divers wear shorties.
Dry Suits. For the longest durations and colder water, you’re going
to need a dry suit. This sometimes provides the back up buoyancy
control you need so you can dive with a single bladder BCD, and
it gives you the option of using an argon inflation system for addi-
tional insulation.
Dry suits require some training and experience
to use properly. If they’re new to you, take the
PADI Dry Suit Diver course and master using dry
suits in recreational diving before using one for
tec. At least 20 dives is a conservative minimum
experience with a dry suit before making a tec
dive in one.
But even after mastering dry suit use in recre-
ational diving, you’ll need some new skills for
tec diving in one. In recreational diving, you use
only the dry suit for buoyancy control under-
water. In a heavy weight tec kit, you’d look like
the Goodyear Blimp if you tried that, so you use
both the suit and your BCD at the same time.
This calls for some valve juggling when ascend-
ing and descending, which is a more complex
skill to master.
Wet Suits. For most tec divers, a full 6 mm/ 1/4 in.
farmer john (or other style with two layers over
the torso) wet suit with hood will suffice in water
24˚C/75˚F or warmer, for two to three hours. Even after mastering dry suit use in recre-
Some divers find that they can even use a wet ational diving, you’ll need some new skills for
tec diving in one, such as controlling both your
suit in substantially cooler water. Be sure to get BCD and your dry suit at the same time.
a good quality suit made of durable neoprene
that can withstand the rigors of compression
and recovery caused by depth and pressure.
Wet suits add some buoyancy variables you need to account for.
When wearing heavy weight rigs, dropping weights in an emer-
gency (if you even need any!) may not give you sufficient buoyancy
if your BCD fails. With lightweight rigs, dropping them may give
you way too much, making it difficult to maintain a deco stop.
Therefore, double wing BCDs are essential. At depth, your suit will
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 be compressed so that it has little buoyancy,
so you need to be sure your BCD has ample
lift. You’ll probably have a lot of gas in it.
When you return to shallower water, the suit
re-expands and buoyancy restores; you need
ample weight so you don’t spend your entire
decompression stop trying to stay down. (You’ll
learn more about proper weighting for a tec
dive in a bit.)
The advantage of wet suits is simplicity. You
only need to control your BCD, and, when div-
ing in environments that can be hard on a suit
(like wrecks), you don’t have to worry about
chattering your teeth through an hour decom-
pression because you snagged it and made a
When diving in a wet suit, choose a double
(redundant) bladder BCD. leak.

Weight Systems
Your choices in tec diving weight systems are
similar to those in recreational diving, but
with differences. For one, you may not need
one at all, and in many instances, the man-
datory quick release you learned to use in rec-
reational diving becomes as much a liability
as an asset.
With light rigs, like double aluminum cyl-
inders, you will probably still need weights.
With heavy weight rigs, you may not, depend-
ing on your exposure suit. Your choices, as in
recreational diving, are the weight belt, the
integrated weight system and the weight har-
ness.
Weight Belt. The advantages of the standard
weight belt are that it is simple, readily avail-
able and easy to adjust. It’s a good choice
One disadvantage of a weight belt is that
when you don’t need much weight. The dis- you have to put it on after you don your
advantages are that you have to put it on rig, otherwise you trap it under the crotch
after you don your rig (otherwise you trap it strap. But, some tec divers intentionally trap
the belt, judging that the risk of losing it by
under the crotch strap), and that it can be
accident is higher than the risk of having to
hard to position securely amid your other release the crotch strap to get rid of it.
gear. The more weight on the belt, the more

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 these disadvantages become an issue. Regarding the crotch strap,
as discussed shortly, losing your weights on a decompression dive

ONE
can be a hazard. With that in mind, some tec divers intentionally
wear their crotch straps over their weight belts for both convenience
and to minimize risk of accidental loss. They do this knowing that
it will slow down ditching the belt if necessary; they balance one
risk against another.
Integrated Weight Systems. These systems inte-
grate with your harness, so their advantages are
that you don’t need to put them on last, and
they’re already positioned amid the rest of your
kit. The disadvantages are that you have to have
a harness system that accepts integrated weights
(many don’t), and it makes an already heavy rig
heavier. Also, you may find the weight system
located in a less than ideal location, adding some
clutter to your rig rather than streamlining it.
Weight Harness. The weight harness provides the
key advantages of both the weight belt and weight
system while eliminating some of the disadvantag-
es. They simplify kitting up because you don them
before your rig, and they don’t add weight to the
Weight harnesses simplify kitting up
because you don them before your
rig. The downside is that they can be awkward to
rig, and they don’t add weight to adjust so the rig doesn’t interfere with weight ditch-
the rig. ing, and they sometimes get a bit in the way when
sliding into your kit.
Loss of Weights. Losing your weights can be a significant haz-
ard on a decompression dive when you’re in a lightweight rig.
Accidental weight loss can make it difficult
or impossible to control your ascent, much
less maintain the depths for required decom-
pression stops.
To avoid this possibility with weight belts,
many tec divers mount two buckles, both of
which you must release to get rid of the belt.
The slightly slower ditching time is more
than offset by the hazard it helps avoid.
Most weight systems and harnesses are less
prone to accidental loss than weight belts, To avoid the possibility of accidental weight belt loss,
many tec divers mount two buckles, both of which
so you usually don’t need to do this with you must release to get rid of the belt. To them, the
them, though you can arrange some so their slightly slower ditching time is more than offset by the
release mechanisms take two steps. hazard it helps avoid.

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 Similarly, as mentioned before, some divers intentionally wear their
crotch straps over their weight belt. The drawback is that this would
delay getting rid of it quickly in an emergency.

Instrumentation
Your basic deep technical kit instrumentation includes your SPG
(on the left post regulator), compass, dive computer or timer/depth
gauge, and back up computer or timer/depth gauge. You arm
mount these (except your SPG, of course), and some tec divers carry
their compass in a pouch or pocket.
As a rule, tec divers avoid consoles. They’re
bulky and protrude, creating drag and an
entanglement hazard — quite contrary to
the standardized technical rig philosophy.
To save arm space, however, tec divers
sometimes mount two gauges on a single
wrist strap. Some tec divers carry back up
gauges clipped inside a pouch or pocket.
SPG (Submersible Pressure Gauge). You
only have one of these because two creates
As a rule, tec divers avoid consoles. They’re bulky and the potential for two high pressure leaks. If
protrude, creating drag and an entanglement haz- your SPG fails, you’ll end the dive immedi-
ard – quite contrary to the standardized technical rig
philosophy. Instead, tec divers mount their gauges on ately anyway.
their arms.
The preferred SPG is the simple, mechani-
cal type because it’s reliable (no battery
concerns). Few tec divers use air integrated computers, whether with
hose or hoseless. They’re electronic, tend to be bulkier, and if the
gauge fails, you’re out two, rather than one instrument.
Compass. Your standard full sized, liquid filled diver’s compass
does the job for most tec diving, though some tec diving
(cave) calls for specialized compasses for surveying and
mapping.
Timer and Depth Gauge. These may be separate instru-
ments, though most tec divers prefer the integrated digi-
tal depth gauge and bottom timer. Digital watches suit-
able for scuba diving with a stop watch function provide
a timer option, provided that they’re rated to the depths
You should always have at
you’re planning to dive. least two methods for deter-
mining your time, depth
You use a timer/depth gauge in place of a dive computer
and decompression require-
when diving with tables, or you may use it with tables as ments.

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 back up to your computer. If you’re using two computers, you don’t
also need a timer/depth gauge; but you should always have at least

ONE
two methods for determining your time, depth and decompression
requirements.
Dive Computers. At this writing, there are three types of
dive computers suitable for the diving you’ll be doing
as a DSAT Tec Deep Diver or Apprentice Tec Diver: the
standard air computer, the enriched air computer, and
the multigas computer. Given the rapid changes in this
technology, you may have more choices by the time
you read this.
Air computers – The basic air-only computer has the
advantages of being simple, inexpensive and always
yields a more conservative decompression profile when
using enriched air nitrox. The downsides are that Single gas enriched air dive computers
they’re limited in the performance they offer, they can’t allow you to set for the EANx you’re
extend your no stop limits or shorten your deco type using, usually with up to 40 or 50 per-
cent oxygen. They extend your no stop
with EANx, and they don’t track your oxygen exposure. time and shorten your decompression
when using EANx versus air.
Enriched air computers – These allow you to set for the
EANx you’re using, usually with up to 40 or 50 percent
oxygen. Their advantages are that they extend your no
stop time and shorten your decompression when using
EANx versus air, and they’re not as costly as multigas
computers. The disadvantages are they cost more than
air-only computers, and they’re limited compared to
multigas computers because they don’t further extend
your no stop time or shorten your decompression when
you switch gases during the dive. They also can’t track
your oxygen exposure if you switch to a higher oxygen
gas during the dive. You can set multigas enriched air com-
puters with three or more EANx blends
Multigas computers – You set these computers with or pure oxygen, allowing the computer
three or more EANx blends or pure oxygen, allowing to alter your decompression and oxy-
the computer to alter your decompression and oxygen gen exposure when you switch from
one gas to another during the dive.
exposure when you switch from one gas to another
They can extend your no stop time,
during the dive. The advantages are that they can accelerate your decompression based
extend your no stop time, accelerate your decompres- on the gas switches, and track your
sion based on the gas switches, and track your oxygen oxygen exposure.

exposure. This is the most versatile computer type for

tec diving.
Multigas computer disadvantages are that they’re also the most
costly, and they are more complicated to use. This means more
potential for error. Some types require you to link the dive computer
to a personal computer to load it with the information for the dive.
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 You’ll learn more about using all three types of computers as you
go through the course.

Cutting Tools
By now you’ve noticed that technical divers are big on back
ups, so it’ll come as no surprise that you should have at
least two cutting tools when tec diving. Of these, you want
to carry at least one so you can retrieve and use it with
either hand.
You have several options in cutting tools and where you
wear them. The standard dive knife, if sharp and in excel-
lent condition, will do the job. But, the trend in tec diving
is away from the big dive knife (and it’s never worn in cave
diving); those who opt for it usually wear it on the inside of
either calf so you can reach it with either hand, and so it’s
not prone to entanglement.
The standard dive knife, if sharp
and in excellent condition, will More commonly you’ll see a small dive
do the job for some tec diving,
but, the trend is away from
knife worn in a sheath near the cen-
the big dive knife. When used, ter of the waist band, again so either
it usually goes on the inside of hand can get it, but sometimes on the
either calf.
harness shoulder. This knife is usually
very sharp, so you have to be careful
unsheathing and sheathing, since you may not
be able to see the sheath. That is to say, don’t
accidentally cut your equipment or yourself.
The Z-knife, or hook knife, is a
small bladed hook especially
suited for cutting fine line. It’s
commonly mounted on the wrist
or harness. More commonly you’ll see a small dive
knife worn in a sheath near the center
EMT shears are heavy duty snips of the waist band where either hand can
that can cut rope, or (for some get it. With the setup shown, the sheath
models) even cable. Wreck div- bands also hold the free end of the waist
strap to improve streamlining.
ers especially go for these as an
alternative to a knife, wearing it
The Z-knife, or hook knife, is a small on the harness, calf or waist. They’re also popular in
bladed hook especially suited for cutting
fine line. It’s commonly mounted via
cool water environments that make it hard to handle
gauge strap on the wrist or harness. a knife while wearing thick gloves.
Since you can’t see your waist very well, another
option is to carry a bosun’s knife or other folding knife in a sheath
or pouch at the waist or under your instrument wrist straps. The

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 advantage of a folding knife is that closed,
you can handle it safely even when you

ONE
can’t see it. You usually have a clip or
wrist lanyard on it to prevent loss while
handling, and most tec divers go for types
that you can open with one hand. Since
these aren’t true dive knives, unless you
opt for titanium, they need extra care to
prevent excessive corrosion.
For specific dive objectives, you might
Another option is to carry a bosun’s knife or
carry a Leatherman®-type multi tool in
other folding knife in a sheath or pouch at the
a sheath or pouch on your waist band,
waist or under your instrument wrist straps. The
or in a pocket with a clip.
advantage of a folding knife is that closed, you
Typically these include a
can handle it safely even when you can’t see it.
You usually have a clip or wrist lanyard on it to
knife blade, pliers, wire cut-
prevent loss.
ters, a file, saw and some
other tools. They’re versatile, but can be difficult to
open with gloves on. In selecting one, you might wear
your dive gloves to see how well you manage.
In selecting and mounting your cutting tools, keep in
mind that different environments and objectives will
call for different tools and mounting requirements.
Your instructor can help you select the optimum cut-
For specific dive objectives, you might
ting tools for the environment in which you train for carry a Leatherman®-type multi tool in a
the Tec Deep Diver or Apprentice Tec Diver certifica- sheath or pouch on your waist band, or
tion. in a pocket with a clip.

Guidelines for Pockets, Clips and Accessories

As you gain experience in tec diving, you’ll find that
you’re continuously needing to update what you
carry and how you carry it to meet specific dive objec-
tives and environmental configurations. Your goal
is to stay with the rig-wreck, dive-cave philosophy —
minimal drag, nothing dangles, everything out of the
way but easy to get to when you need it. Try to apply
these six guidelines:
1. Avoid large pocket pouches on your harness. These
tend to add bulk and confusion to your rig and get Avoid large pocket pouches on your har-
ness. If you need a pocket on your rig,
in the way. If you need a pocket on your rig, like for
choose a small pocket that slides back
a spare mask, choose a small pocket that slides back and out of the way.
and out of the way.

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 2. The most useful pocket in tec diving is on the
outside thigh of your exposure suit. Since it’s
well below your rig, you can get to it even when
wearing multiple stage/deco cylinders. If your
exposure suit doesn’t have one, you can usually
get one added, and some manufacturers make
strap on thigh pockets that work well. If you’ll
be investing in a new exposure suit soon, be
sure to order the pocket with it.
3. Use brass or stainless steel clips for your
accessories and SPG. Mount the clip onto the
accessory, not on the BCD or harness. Generally
avoid plastic (not very strong) and chrome-plat-
ed (corrode and jam) clips.
4. Sliding gate clips (a.k.a. “dog clips”) are
generally preferred over marine snaps (a.k.a.
“swinging gate clips) because they won’t acci-
dentally snap on to things by themselves like
the latter can. (In some areas, wreck divers call
The most useful pocket in tec diving is on the marine clips “suicide clips” because they can
outside thigh of your exposure suit. Since it’s
well below your rig, you can get to it even when
potentially clip themselves
wearing multiple stage/deco cylinders. to line or cable, entan-
gling you underwater.)
However, this is over
emphasized, and a few tec divers use marine
clips without any difficulties. In any case, all
clips should be where you can access them
(nothing outside of reach) because all clips
can snag and you may need to disentangle
them.
Keep the environment in mind. Smaller clips
that you work easily with thin gloves in warm
water may be impossible to open and close in
cool water with thick gloves.
5. Accessories clipped to a D-ring should be
well out of the way when stowed, and not
dangle or create entanglement potential. If
possible, keep an accessory in a pocket except
when in use, and clip it to your harness only Accessories clipped to a D-ring should be
well out of the way when stowed, and
to free your hands momentarily, or to avoid
not dangle or create entanglement poten-
dropping the item while using it. As possible, tial. As possible, try to put only one item per
try to put only one item per D-ring. D-ring.

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 6. Use a breakaway clip on anything you may need
to discard or release in an emergency. To make a

ONE
breakaway clip, connect the clip to the accessory or
gauge via a small o-ring. In an emergency, a sharp
tug breaks the o-ring to free the item, leaving the clip
behind on the D-ring. Small pull ties break away eas-
ily with a 90 degree twist.

Putting It All Together: Basic Rig Use a breakaway clip on anything

Head-to-Toe you may need to discard or release
in an emergency. To make a break-
Okay, now that you’ve got the basics about your tec away clip, connect the clip to the
rig components, let’s look at how it all fits together. accessory or gauge via a small
o-ring. Small pull ties break away
Regulators and Valves. Start with your short hose easily with a 90 degree twist. This
regulator on the left post. Your SPG goes straight item uses both.
down behind the BCD wing and mounts via break-
away clip on your left hip D-ring. (Some divers mount
it up on a chest D-ring.) The second stage goes to the right and
rests on your upper chest, held there by a bungee or surgical tubing
necklace. If you’re using double wings, the low pressure (LP) infla-
tor hose goes to the right or straight down to the back up inflator
mechanism (depends on its location). If you’re using a dry suit,
with most suits the LP inflator hose goes straight down, then back
up at the left hip to the inflator. If you’re using an argon system
and a single bladder BCD, then there will be no LP inflator hose.
Your long hose regulator goes on the right post, so that the low
pressure inflator hose goes to the left to the primary BCD inflator,
and the long hose goes straight down behind the wings. From there
it tucks under the right D-ring and safety reel (you’ll learn more
about safety reels in the next chapter), comes up across your chest,
behind your neck on the left and around to your mouth from the
right. Mount a breakaway clip where the second stage meets the
hose for clipping it off when it’s not in your mouth. When kitting
up, you swing the long hose into place as your last step so that
you’re sure that no hoses or gear trap it by lying on top.
In mounting and rigging your regulators, note that all hoses come
off the first stages so they go inward and/or downward — never
outward so they protrude. Proper routing maintains your streamlin-
ing and minimizes entanglement hazard.
Open all the valves, including the isolator valve all the way. Do not
close them back a partial turn like some used to do in recreational
diving.

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 Short hose to
LP hose to
backup second
primary BCD
stage

SPG hose

LP hose to
Long hose to backup BCD
primary second
stage

Mount your regulators so hoses route inward and downward.

BCD and Harness. Your primary BCD inflator hose comes over
your left shoulder, retained (clip or strap) so you don’t have to hunt
for it, but easy to release so you can quickly dump gas. Your back
up BCD (if used) inflator stays behind the BCD wing on the right or
left (depends on how your BCD’s laid out), clipped to the wing or
bungeed to the cylinders. This avoids confusion with the primary
(remember, you only use one at a time), while keeping the back
up readily available. Some divers leave the back up BCD inflator
hose disconnected,
especially if using high
volume inflators, to
avoid an accidental
runaway ascent if the
inflator malfunctions.
The drawback is that
this adds a step if you
have to switch to your
back up in a hurry.
If you’re using a dry
suit, ideally you want
the BCD hose to be
Secure the backup BCD inflator behind the bladder with either a snap (left), or by long enough that you
tucking it under inner tubing at the base of the cylinder (right).
can control both the
BCD inflator and dry
suit inflator at the same time with the left hand. This lets you add
air to both at the same time as you descend, keeping your right
hand free for other uses.

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 Pockets, if used, should be small and mounted at or near the hips
as previously noted, well out of the way. Straps should be adjusted

ONE
and/or trimmed so there’s no excessive slack dangling from any
slide or buckle. The crotch strap should normally be under your
weight belt (if used — and some divers opt to wear it over the belt
as discussed earlier). The harness height on the cylinders should
be adjusted so that you can reach both regulator valves and the
isolator valve. It’s acceptable if you need to loosen your waist
and/or crotch strap to do this.
Exposure Suit. If you’re using an argon system, the argon cylin-
der mounts on the left side, valve down with the regulator inward
so you can open the valve while wearing your rig (same as in
recreational diving), though some divers prefer wearing it on
the right because it matches their suit’s layout better. Thread the
LP hose to the dry suit inflator under your harness to eliminate
protruding slack. Ideally, mount the system with a bracket that
includes straps that you can cut (not all metal) to release it in an
emergency.
As mentioned before, you’ll find a thigh pocket the most useful
pocket location in tec diving. It’s also worth having knee pads;
you’ll find that you’re especially hard on the knees in tec gear.
Instruments. Wear instruments on your arm on either side as you
prefer. You may find that mounting all on one side, leaving one
arm “clean” makes it easier to slide in and out of your rig (clean
arm goes in last kitting up, and comes out first getting out). In
some instances (such as scootering in a cave), arm choice may
be more important for procedural reasons, but these cases don’t
apply to this course.
In setting up your instrument stack, if you plan to use it, put your
compass so you can center it with your body line for accurate
navigation. Otherwise, it’s cleaner to opt to carry it in your thigh
pocket if you don’t plan to use it — but you should have it in case
you need it. Keep in mind that you can put more than one gauge
on a single strap. Remember that you should have information
back up with either two dive computers, one computer and one
depth gauge/timer/tables, or two depth gauges/timers/tables.
Mask and Fins. Forget the snorkel for most dives. If possible, you
can wear your mask strap under your wet suit hood (not all hoods
will let you do this, though), which minimizes the chance of slip-
ping off, and helps keep it in place even if the strap breaks. If you
have a spare mask, it tucks in an out-of-the-way harness pocket
or thigh pocket (more about spare masks in the next chapter.)

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 Preadjust your fins. If they’re not adjustable while wearing them,
tape or otherwise secure the straps so they can’t slip. Inspect the
straps frequently (and the mask strap); they’re one of the most
common but avoidable gear failure points.
When you’re in the
water, your mask is on
your face. Period. But,
when you’re gearing up
or just after getting out,
you may want it handy
but out of the way.
Many tec divers simply
put it on backward,
with the strap across Before the dive, you can stick your mask on the back of your head to keep it
their forehead, until with you, but out of the way (left). Many tec divers prefer to wear the mask
strap under their hoods while diving (right).
they need it.
Weight System. If you
use weights, the weights need to be secure, but free and clear for
ditching. If you’re using a back up buckle on a weight belt, check
that it’s secure.
Cutting Tools. You should have two, mounted appropriately for
the type, with at least one retrievable by either hand.
This describes the basic rig used by most tec divers, though there
are regionalized variations for different types of environments.
As you’ll discover in the training dives, standardization plays an
important part in how you function, particularly when following
procedures in an emergency. Therefore, any departures from stan-
dard rigging need to be discussed with and agreed upon by your
dive team.

Maintenance
Take care of your gear and your gear takes care of you.
That’s the mantra of leading tec divers the world over; make it
yours, too. Here are four recommendations regarding equipment
maintenance:
1. Maintain it according to the manufacturer specifications.
2. Have regulators, valves, BCDs and gauges inspected and ser-
viced/overhauled (as appropriate) at least annually, or more fre-
quently for heavy use or as manufacturer specified.

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 3. Have any equipment that doesn’t appear to function normally
inspected and serviced before using it.

ONE
4. Never dive with gear in anything but top shape. Doing other-
wise raises your risk of injury — or death — because you’re starting
the dive with a potential problem. Diving with gear in less than
ideal working order is essentially using your back up from the start
of the dive. That’s outright stupid — if your back up has no back
up, then guess what. You’re diving without a back up. Diving with-
out back up is what injures and kills divers in technical diving envi-
ronments. Don’t be stupid.

Tec Exercise – 1.2

1. You apply the standardized technical rig phi- 6. You choose your harness considering these characteris-
losophy to ________________ ______________ tics (check all that apply):
and ________________ ___________ due to a. style c. crotch strap availability
_______________ _______________ ____________. b. adjustable D rings d. waist strap types

2. When choosing mask, fins and snorkels for tec diving 7. When diving in a ________ suit, you should always
you want (check all that apply): have a double wing BCD.
a. a compact, high quality scuba mask.
8. Of your weight system options, the one that’s simplest
b. full size power fins. and easiest to adjust is:
c. a flex snorkel with a wide bore. a. the weight belt.
d. fins without vents. b. the integrated weight system.
c. the weight harness.
3. The prime choice for a manifold is a(n)
________________ system __________ manifold. d. None of the above.

4. You want at least _____________ independent regula- 9. When tec diving, you’ll generally use wrist mount
tors when tec diving. The one on the ______________ gauges (excepting your SPG) that include a compass
and two ways of monitoring depth, time and decom-
side has the ________________ hose that you breathe
pression requirements.
from and hand to a team mate in an emergency.
True False
5. You choose a BCD for your individual and environ-
mental needs based on these characteristics (check all 10. Of the three types of computers suitable for the tec
that apply): diving you’ll be qualified for as a Tec Deep Diver, the
a. size ________________ computer offers the most versatility,
b. ballistic material but costs the most and is the more complex to use.
c. single or double bladder
d. unrestrained or bungeed design

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 Tec Exercise – 1.2 continued

11. Which of the following statements is NOT true? 13. Recommendations for maintaining your gear include
a. You should have at least two cutting tools when (check all that apply):
tec diving. a. Maintain it according to manufacturer specifica-
tions.
b. You can carry a Z-knife for cutting lines quickly.
b. Have regulators, valves, BCDs and gauges
c. At least one cutting tool should be accessible by
inspected and serviced annually.
either hand.
c. Have any equipment that doesn’t appear to func-
d. The standard large dive knife is never acceptable
tion normally inspected and serviced before using it.
in tec diving.
d. Never dive with gear in anything but top shape.
12. Guidelines regarding pockets, clips and accessories
include (check all that apply): 14. Which of the following statements is not true?
a. Use a thigh pocket on your exposure suit rather a. The LP hose to your primary BCD inflator comes
than a large pouch on your harness. off the right post regulator.
b. Mount brass or stainless steel clips to accessories, b. Your primary regulator has a breakaway clip
not to your BCD or harness. where the second stage meets the hose.
c. Choose sliding gate clips over marine snaps. c. Open all valves, including the isolator, all the
way, without closing them back a partial turn.
d. Put breakaway clips on anything you might need
to ditch or release in an emergency. d. Always route hoses from the first stage outward
and upward so they don’t interfere with each other.

Check it out:
1. minimize confusion, procedural error, equipment task loading. 2. a, b. c is not true because you don’t use a snorkel at all; d is
not true because vents or their lack is not an issue. 3. DIN, isolator. 4. two, right, long. 5. a, c, d. b is not true because material
is not generally an issue. 6. a, b, c, d. 7. wet. 8. a. 9. True. 10. multigas. 11. d. The standard large dive knife is not acceptable in
some forms of tec diving, but it is acceptable in others. 12. a, b, c, d. 13. a, b, c, d. 14. d. You always run your hoses inward and
downward so they don’t protrude.

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 Gas Planning I

ONE
Most technical deep diving wouldn’t be feasible
without the ability to select the gas blends you
need. If you could only use air, you’d have less
reliability in your decompression (i.e. a higher
DCS risk), and you might not be able to carry
enough gas to complete your decompression.
As a Tec Deep Diver, you’ll be using various
blends of EANx and oxygen to maximize your
no stop time, to minimize your decompression
and to accelerate your decompression. As an
Apprentice Tec Diver, you’ll learn to switch
EANx blends to extend your no stop dive time.
This section begins developing your gas plan-
As a Tec Deep Diver, you’ll be using ning skills, starting with a review of concepts
various blends of EANx and oxygen to and terms you already know from previous
maximize your no stop time, to minimize training. From there, you’ll move into new ter-
your decompression and to accelerate
your decompression. As an Apprentice Tec ritory, particularly involving oxygen exposure
Diver, you’ll learn to switch EANx blends and how you track it.
to extend your no stop dive time.

Tec Objectives
Highlight or underline the answers to these questions as you find them:

1. What is an Equivalent Air Depth (EAD) and how do 8. How do you determine how much gas a cylinder
you find it? has?
2. What are the maximum recommended oxygen 9. What are CNS oxygen toxicity and pulmonary oxy-
partial pressures for deep technical diving? gen toxicity, and what causes each?
3. What determines the maximum depth you can use 10. What are the signs and symptoms of CNS oxygen
an enriched air blend during the working (bottom) toxicity?
phase of the dive?
11. What are the signs and symptoms of pulmonary
4. What determines the maximum depth you can use oxygen toxicity?
an enriched air blend during the decompression/
12. What is the so-called “CNS clock”?
safety stop phase of a dive?
13. What are Oxygen Tolerance Units (OTUs)?
5. How do you find your Surface Air Consumption
(SAC) rate? 14. What methods do you use for managing oxygen
exposure?
6. How do you use your SAC rate to estimate your
gas supply requirements for a given depth and 15. What is the primary way you avoid CNS oxygen
time? toxicity while diving with air, enriched air or pure
oxygen?
7. How do you determine your reserve gas supply ?

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 Equivalent Air Depth (EAD)
In your PADI Enriched Air Diver course, you learned that an EAD
(Equivalent Air Depth) is an adjusted depth you use on air tables
when using enriched air nitrox. For a given actual depth with
enriched air, the EAD is the depth at which air has the same nitro-
gen partial pressure (PN2). You use the EAD depth, rather than the
actual depth, to determine your no stop limits and repetitive dive
status with air tables. EANx has less nitrogen than air has, so the
EAD is shallower than actual depth — hence the longer no stop
times.
There are two ways to find EADs, and two methods that provide
your decompression information without the need for EADs. The
first is to use the EAD formulas:

METRIC

EAD = (1-fraction of oxygen) x (Depth in metres+10) -10

.79

IMPERIAL

EAD = (1-fraction of oxygen) x (Depth in feet+33) -33

.79

(If you need a refresher in using the EAD formula, see the PADI
Enriched Air Diver Manual. Remember to express the fraction of
oxygen as a decimal; e.g., 32% oxygen, use .32.)
Although the EAD formula does the job, you know from your own
experience that you don’t use it about 99.9999999% of the time
because it’s a pain in the rear and seldom produces a meaning-
ful benefit. In reality, you simply look the EAD up on a table such
as the DSAT Equivalent Air Depth Table (for EANx30 through
EANx40), or the Equivalent Air Depth and Oxygen Management
Table in the appendix of this manual (air through 100 percent oxy-
gen).
For instance, what’s the EAD for 18 metres/60 feet if you’re div-
ing with EANx29? Using the Equivalent Air Depth and Oxygen
Management Table, you should quickly find that it is 15.2
metres/51 feet. If you need a review on finding EADs, see the PADI
Enriched Air Diver Manual and/or your instructor. It’s crucial that
you’re able to do so for this course and for this type of diving.

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 METRIC IMPERIAL

EQUIVALENT AIR DEPTH AND OXYGEN EQUIVALENT AIR DEPTH AND OXYGEN

ONE
MANAGEMENT TABLE – METRIC MANAGEMENT TABLE – IMPERIAL

OXYGEN CONTENT 29% OXYGEN CONTENT 29%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 1.7 0.38 –– 0.00% 10 6 0.38 –– 0.00%

5 3.5 0.44 –– 0.00% 15 10 0.42 –– 0.00%
6 4.4 0.46 –– 0.00% 20 15 0.47 –– 0.00%
9 7.1 0.55 0.15 0.14% 30 24 0.55 0.16 0.14%
12 9.8 0.64 0.34 0.17% 40 33 0.64 0.35 0.17%
15 12.5 0.73 0.52 0.22% 50 42 0.73 0.52 0.22%
18 15.2 0.81 0.68 0.28% 60 51 0.82 0.69 0.28%
21 17.9 0.90 0.83 0.28% 70 60 0.91 0.84 0.33%
24 20.6 0.99 0.98 0.33% 80 69 0.99 0.99 0.33%
27 23.3 1.07 1.12 0.42% 90 78 1.08 1.13 0.42%
30 25.9 1.16 1.26 0.48% 100 87 1.17 1.27 0.48%
33 28.6 1.25 1.40 0.55% 110 96 1.26 1.41 0.55%
36 31.3 1.33 1.53 0.67% 120 105 1.34 1.55 0.67%
39 34.0 1.42 1.66 0.83% 130 113 1.43 1.68 0.83%
42 36.7 1.51 1.79 2.22% 140 122 1.52 1.81 2.22%
45 39.4 1.60 1.92 2.22% 150 131 1.61 1.94 2.22%

One way to get the decompression

information you need for a particular
enriched air blend is to use desk top
decompression software, which you’ll be
learning to use as you get further into
the Tec Deep Diver course. Desk top deco
software generates custom tables for the
particular enriched air blend or blends
you’re using, eliminating the need for
EADs altogether.
Similarly, an enriched air dive computer
automatically determines EADs as part
of its calculations, so as you realize, you
don’t need EADs to use it. However, you An enriched air dive computer automatically determines
EADs as part of its calculations, so you don’t need EADs to
may still need EADs if your back up deco
use it. However, you may still need EADs if your back up
information employs an air table. deco information employs an air table.

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 Maximum Blend Depth
Atmospheres You also recall from your PADI Enriched Air Diver
and Bar course that in recreational enriched air nitrox diving,
the maximum allowable oxygen partial pressure (PO2)
By convention, whether is 1.4 ata. The Maximum Depth for using a particular
in a metric system or an blend of enriched air when recreational diving is deter-
imperial system country, mined by the depth at which the PO2 reaches 1.4 ata.
the international dive com-
munity uses “atmospheres In tec diving, things differ a bit. During the bottom or
absolute” (ata) to express working part of the dive, the maximum allowable PO2
gas partial pressures and is 1.4 ata, just as in recreational diving. And, just as in
absolute pressure at depth. recreational diving, limiting your maximum PO2 to less
Although there’s techni- than 1.4 ata is always a good idea, especially if swim-
cally a slight pressure dif- ming or working hard (exertion is thought to predispose
ference between a bar and you to oxygen toxicity).
an atmosphere, for the
purposes of diving you can However, during decompression, a higher PO2 is consid-
consider ata and bar as the ered acceptable because you’re relaxed and not exerting
same thing. yourself. For decompression purposes, the maximum
depth that you can use an EANx blend is the depth at
Note that all other pressure
references, such as cylin- which that blend reaches a PO2 of 1.6 ata. However,
der pressures, use bar for keep in mind that this assumes that you’ll be at rest.
the metric system and psi It’s a good idea to be more conservative and use a lower
(pounds per square inch) maximum PO2 when possible, especially if there’s a
in the imperial system. good chance that you’ll be exerting yourself during
decompression. If you’re using enriched air for extra
conservatism rather than accelerated decompression
(more about these in chapters to come), limiting your decompres-
sion PO2 to 1.4 ata is easy
and offers some added con-
servatism.
Remember that oxygen tox-
icity is unforgiving. If you
had to choose, it’s better to
get DCS (which is usually
treatable) than an underwa-
ter convulsion that leads to
drowning (which is usually
untreatable).
Incidentally, in the imperial
system tec divers routinely
Remember that oxygen toxicity is unforgiving. If you had to
treat 20 feet as the maxi-
choose, it’s better to get DCS (which is usually treatable) than an
mum depth for 100 percent underwater convulsion that leads to drowning (which is usually
oxygen and make their first untreatable).

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 oxygen stop (if using it) at that depth. Technically, the PO2 of pure
oxygen at 20 feet of sea water is 1.61 ata. The .01 difference is

ONE
ignored first because it’s physiologically insignificant, and second
because the difference between 1.61 and 1.6 ata is less than three
inches!
Finding Your Maximum Depth. As you already know from your
PADI Enriched Air Diver course, you can find your Maximum
Depth by using formulas:

METRIC

Bottom max depth (1.4 ata) = ( fraction 14of oxygen ) - 10

Deco max depth (1.6 ata) = (
fraction of oxygen )
16 - 10

IMPERIAL

Bottom max depth (1.4 ata) = ( fraction46.2

of oxygen )
- 33

Deco max depth (1.6 ata) = (

fraction of oxygen )
52.8 - 33

You should already be familiar with using these, but like EADs,
in reality you almost never use them, instead opting to find them
more easily on tables such as the DSAT Equivalent Air Depth Table
(EANx30 through 40) or the Maximum Depths Tables found in the
Appendix of this manual. Most desk top decompression software
will also tell you maximum depths for a given blend.

MOD, Maximum Depth, Maximum

What The . . .?

M
aximum Depth, Maximum winded, so divers (who love to create
Operating Depth, MOD — long names for everything but then actu-
they’re all names for the same ally use a short form) began abbreviating
thing. Originally the label “Maximum two ways: The first was to use “MOD”
Operating Depth” got pasted on the (Just what we needed! Another acro-
depth at which you reach a PO2 of 1.4 nym!), and second was to drop the word
ata/1.6 ata. However, that’s a bit long “operating,” which is superfluous.

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 What’s the maximum bottom depth (1.4 ata) and decompression
depth (1.6 ata) for EANx75? Using the Maximum Depths Tables,
you should find 9 metres and 11 metres/29 feet and 37 feet, respec-
tively. As with EADs, if you don’t recall how to find Maximum
Depths, see the PADI Enriched Air Diver Manual and/or your instruc-
tor. It’s crucial that you’re able to do this for this course and for this
type of diving.

METRIC IMPERIAL

MAXIMUM DEPTHS IN MAXIMUM DEPTHS IN

METRES OF SEAWATER FEET OF SEAWATER
BLEND @1.4 @1.6 BLEND @1.4 @1.6
60% 13 17 60% 44 55
61% 13 16 61% 43 54
62% 13 16 62% 42 52
63% 12 15 63% 40 51
64% 12 15 64% 39 50
65% 12 15 65% 38 48
66% 11 14 66% 37 47
67% 11 14 67% 36 46
68% 11 14 68% 35 45
69% 10 13 69% 34 44
70% 10 13 70% 33 42
71% 10 13 71% 32 41
72% 9 12 72% 31 40
73% 9 12 73% 30 39
74% 9 12 74% 29 38
75% 9 11 75% 29 37
76% 8 11 76% 28 36
77% 8 11 77% 27 36
78% 8 11 78% 26 35
79% 8 10 79% 25 34
80% 8 10 80% 25 33

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 The T Formula

ONE
In tec diving, you’ll often find yourself trying to To use the formula, simply cover what you
determine your PO2 at a specific depth for a specific want to find and do what’s left. If you want
gas blend, or trying to determine at what depth the PO2, multiply the fraction of oxygen by
you reach a specific PO2 with a specific gas blend, absolute pressure (depth). If you want the
or trying to determine what gas blend you would absolute pressure (depth), divide the PO2
use for a specific PO2 at a specific depth. by the fraction of oxygen. If you want the
fraction of oxygen, divide the PO2 by the
The tables and formulas you learn to use in this
absolute pressure.
course simplify this, but in a pinch there’s one for-
mula that will answer all these for you. It looks like
this:
PO2 For example:
What’s the PO2 using EANx40 at
FO2 P 10 metres/33 feet?
Where: FO2 = .4, P = 2 ata., .4 x 2 = .8 PO2
PO2 = partial pressure of oxygen in ata
Using EANx40, at what depth do you reach
FO2 = the fraction of oxygen in the blend
a PO2 of .8?
and P = absolute pressure in ata
FO2 = .4, PO2 = .8, .8 ÷ .4 = 2 ata, 2 ata =
10 metres/ 33 feet
Remember that your absolute pressure is the depth:
METRIC If diving to 10 metres/33 feet, what percent
(D + 10) ÷ 10 = absolute pressure in ata (bar) oxygen do you need to have a PO2 of .8?
PO2 = .8, P = 2 ata, .8 ÷ 2 = .4 (40 percent)
and (ata x 10) -10 = D

IMPERIAL
(D + 33) ÷ 33 = absolute pressure in ata
and (ata x 33) -33 = D

Gas Consumption
During the PADI Deep Diver course and in the PADI Deep Diver
Manual, you learned the basics of gas planning and determining
your gas consumption rate. It’s a useful skill in recreational diving,
but to a degree optional in that when your SPG says it’s time to go,
you go. It usually doesn’t matter (at least from a safety standpoint)
if you breathe faster than you thought, provided you keep an eye
on your SPG and adjust your dive so you begin your ascent with
enough time to ascend slowly and make a safety stop at
5 metres/15 feet.

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 Planning your gas consumption becomes much more important in
technical deep diving. Put simply, if you owe 30 minutes hang time
but have only enough gas to stay 15 minutes, you’re in a world of
hurt. As part of the Tec Deep Diver and Apprentice Tec Diver cours-
es, you’ll learn to plan how much gas you need based on how fast
you consume it at the surface and at depth.
SAC Rate and RMV. Step one in making sure you have enough gas
for a dive is determining how fast you use it. This is most common-
ly done with your Surface Air Consumption (SAC) rate, also referred
to as your Respiratory Minute Volume (RMV).
Your SAC rate is the rate you use gas (in litres or cubic feet per min-
ute) when swimming at a moderate speed in all your equipment at
0 metres/feet. Equipment and anything that affects your profile will
affect your SAC rate, and your SAC rate changes as you gain skill,
become more fit and with variables such as water temperature.
Your SAC rate also differs from the working part of the dive (when
you’re swimming a lot) and the decompression part of the dive
(when you’re reasonably still). SAC rate can also be calculated in
bar/psi per minute, but that’s not useful in tec diving because that
assumes you’re using the same type cylinder (pressure and volume)
for every dive. That almost never happens in tec diving, so your
SAC rate should be based on volume (litres/cubic feet).
Respiratory Minute Volume (RMV) is defined as:

RMV = Vt -Vd x respiratory rate

where Vt = tidal volume
Vd = respiratory dead air space
respiratory rate = breaths per minute.

Tec divers sometimes use RMV interchangeable

with SAC rate (based on volume). This isn’t tech-
nically accurate, but close enough and no big
deal. Just don’t confuse SAC rate based on psi/bar
with SAC rate/RMV based on volume. They’re not
the same thing.
Finding Your SAC Rate. The only way to find
your SAC rate is to gear up, get wet and use your
SPG, depth gauge and watch. Do this: Put on all
The only way to find your SAC rate
the equipment you’ll be using, then swim at a is to gear up, get wet and use your
moderate pace (not taking it easy, but not get- SPG, depth gauge and watch.
ting out of breath) at a level depth for at least ten

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 minutes, noting your SPG pressure when you start and when you
finish.

ONE
Now all you have to do is plug your depth, time and the pres-
sure you used into this formula, which converts the higher gas
consumption at depth, bar/psi consumed and the total time into
your volume per minute, surface rate. If you’re Metric/Imperial
bilingual, you’ll note a slight difference in how the formulas work,
which comes from the different conventions for referring to cylinder
capacity in the two systems.

METRIC

litres per minute SAC = bar used x total cylinder capacity litres ÷ min
(depth in metres + 10) ÷ 10
Example: You use 25 bar with twin 12 litre cylinders (total 24 litres capacity) while swim-
ming at 15 metres for 10 minutes.
25 x 24 600 ÷ 10 = 24 litres per minute SAC rate
÷ 10 =
(15 + 10) ÷ 10 2.5

IMPERIAL

cubic feet per min SAC = (psi used ÷ working pressure) x total cylinder capacity ÷ min
(depth in feet + 33) ÷ 33
Example: You use 370 psi with twin 71 cubic foot cylinders (142 total capacity, working
pressure 2475 psi) while swimming at 50 feet for 10 minutes.
(370 ÷ 2475) x 142 ÷ 10 = 21.2 ÷ 10 = .84 cubic feet per minute SAC rate
(50 + 33) ÷ 33 2.5

You may recall that in the PADI Deep Diver course, you determined
your SAC rate in bar or psi instead of volume per minute. This really
simplifies things, but as mentioned before, SAC rate based on bar
or psi assumes you’re always using the same type of cylinder (same
capacity and working pressures). This doesn’t cut it in tec diving
because not only can’t you be sure you’ll use the same type cyl-
inder from one dive to the next, but more than likely, you’ll have
different type cylinders in a single dive! Volume per minute lets you
apply your SAC rate to whatever cylinders you happen to be using.
Your SAC rate while holding still — like when making a decompres-
sion or safety stop — will be considerably less than your working
SAC rate. Therefore, you may want to determine your SAC rate at
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 rest for planning decompression/safety stop gas consumption. That
is, you’ll have a working SAC rate and a decompression SAC rate.
When using your SAC rate (which you’ll get into in a moment),
you adjust your SAC rate up (or down, sometimes) based on your
expected exertion. When in doubt, estimate upward, of course.
Your SAC rate will change as you gain experience and when you
make substantial equipment changes, so you need to recheck it
periodically. During this course, you’ll calculate your SAC rate sev-
eral times — don’t be surprised if it’s never exactly the same twice.
With each calculation, though, you’ll find yourself zeroing in on
working and deco SAC rates that you can employ reliably.
Estimating Your Gas Requirements for a Given Depth. To esti-
mate your gas requirements for a given time at a given depth,
you’ll use your SAC rates, with some decompression software use,
too.
Estimating your gas requirement is simply a matter of plugging
your planned depth, time and SAC rate into the following formula:

METRIC

litres required
= (min x SAC rate) x ((depth in metres + 10) ÷ 10)

Example: If your SAC rate is 22 litres per minute, how much gas
supply do you need for 15 minutes at 33 metres?
litres required = (15 x 22) x ((33 + 10) ÷ 10)
litres required = 330 x 4.3
litres required = 1419

IMPERIAL

cubic feet required

= (min x SAC rate) x ((depth in feet + 33) ÷ 33)

Example: If your SAC rate is .77 cubic feet per minute, how
much gas supply do you need for 15 minutes at 110 feet?
cubic feet required = (15 x .77) x ((110 + 33)/33)
cubic feet required = 11.6 x 4.3
cubic feet required = 49.9

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 ONE
Using the formula is pretty straightforward for a single depth dive,
but becomes a pain in the wazoo when you start figuring out mul-
tiple levels, ascents and decompression stops. In the next chapter,
you’ll learn to estimate your gas supply requirements based on
multiplying your SAC rate by conversion factors from the SAC
Conversion Factors Table in the Appendix. It’s much simpler.

Determining Your Reserve Gas Supply.

Life would be wonderful if your estimates were always exact and
your dive always went as planned. But to allow for the unforeseen
— delays, higher gas consumption than expected, going deeper
than planned requiring more decompression than planned — you
always plan for a reserve. You plan a given percent of your gas
purely for emergencies — the higher the planned percent, the
higher the reserve. If your dive goes as planned, you should have
your entire reserve left. If you think your dive goes as planned, but
you end up having used some of your reserve, then it didn’t go as
planned. (Chances are your SAC rate was off.)
The most common reserve in tec diving is a one-third (33 percent)
reserve. This is called the “rule of thirds,” and it means that you
save one third of every gas you carry purely for contingency use.
To determine your gas requirements with reserve for a given depth
use this formula:

gas volume required = total gas

(1 - reserve)
METRIC
For example: If you estimate you need 1419 litres of a gas,
what’s your gas requirement with a 33 percent reserve?
1419 = 1419 = 2127.4 litres
(1 - .333) .667
IMPERIAL
For example: If you estimate you need 49.9 cubic feet of a gas,
what’s your gas requirement with a 33 percent reserve?
49.9 49.9
= = 74.8 cubic feet
(1 - .333) .667

For the rule of thirds (which you’ll probably use most of the time),
you can simplify the formula as:

gas volume required x 1.5 = total gas

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 This works because, as is painfully obvious at an effortless glance if
you’re a mathematical whiz, multiplying by 1.5 is the same as divid-
ing by .66. If you’re like all the rest of us normal people, take our
word for it or redo the previous examples multiplying by 1.5 and
prove it for yourself.

Actual Gas Supply

It’s one thing to know how much gas you need, and another to know
how much you actually have — what you’ve got when you start the
dive. Fortunately, it’s pretty easy to figure out, though somewhat dif-
ferent in the metric and imperial systems because of the way they des-
ignate cylinders.
Metric System. Tanks are designated by their nonpressurized internal
volume in litres. Simply muliply the designated volume by the pres-
sure in bar; for doubles, multiply that by two:
Example: An 11 litre cylinder has 185 bar in it. What is the available
gas supply?
Answer: 2035 litres. (11 x 185 = 2035 litres).
Imperial System: Tanks are designated by their capacity in cubic feet
at their working pressure. One way to find out how much gas you
have is to divide the actual pressure by the working pressure and mul-
tiply that by the designated capacity. (A/W x C = cubic feet)
Example: An 80 cubic foot cylinder, working pressure 3000 psi, has
2500 psi in it. What is the available gas supply?
Answer: 66.66 cubic feet. (2500 ÷ 3000 = .8333, .8333 x 80 =
66.66 cubic feet).
Another, somewhat more popular method is the baseline method;
a baseline is how many cubic feet cylinders hold per psi, which you
multiply by the actual psi.
To get a baseline, divide the designated capacity by the working pres-
sure. Then muliply the result by the actual pressure.
Example: An 80 cubic foot cylinder, working pressure 3000 psi, has
2500 psi in it. What is the available gas supply?
Answer: 66.8 cubic feet. (To get the baseline: 80 ÷ 3000 =
.0267; .0267 x 2500 = 66.75)
Note the slight difference with the previous example due to rounding.

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 For doubles, simply double the capacity when determining the
baseline, or double the baseline number for the single cylinder.

ONE
Example: A set of double 80 cubic foot cylinders, working pressure
3000 psi, have 1850 psi in them. What is the available gas supply?
Answer: 98.6 cubic feet. (To get the baseline: 80 x 2 ÷ 3000
= .0533; .0533 x 1850 = 98.6)
The advantage of the baseline method is that you can determine
the baselines for the cylinders you use frequently and record them
in your log book. Then you only have to mulitply the cylinder base-
line by your SPG reading to determine how much gas volume you
have.
Keep in mind that the popular designation may be rounded.
(Example, some types of the imperial system aluminum “80” actu-
ally hold 78.2 cubic feet at the working pressure). And, the same
cylinders in one region may have a slightly different designation
in another, though the actual capacity is the same. This normally
isn’t a huge issue, but may be if your required gas supply and sup-
ply available are real close.
If you find the gas supply available isn’t adequate for the dive
you’ve planned, you need to re calculate a shorter dive, or get more
gas to cover the dive.

Oxygen Toxicity
In your PADI Enriched Air Diver course, you learned that breath-
ing gases with high oxygen partial pressures poses potential oxy-
gen toxicity, of which there are two forms: Central Nervous System
(CNS) oxygen toxicity and pulmonary oxygen toxicity. As a tec
diver, you’re concerned with avoiding both.
CNS Oxygen Toxicity. Central Nervous System toxicity results from
exposure to PO2s above 1.4 ata during the working/bottom phase
of a dive, and above 1.6 ata during the rest/decompression phase.
High exertion, cold water and some drugs (CNS exciters) may make
CNS toxicity more likely. The oxygen interacts with various bio-
chemical processes within the body, causing a primary symptom/
sign of a convulsion, which as you recall is itself relatively harm-
less. However, a convulsing diver underwater is likely to lose the
mouthpiece and drown, hence the seriousness of the hazard.
Warning signs/symptoms usually do not precede a convulsion, but
if they do, they include visual disturbances, ear ringing or sounds,
nausea, twitching in facial muscles, irritability and restlessness, and

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 dizziness. Remember VENTID - vision, ears, nausea, twitching, irri-
tability, dizziness.
Managing CNS Oxygen Toxicity. Whether using air, enriched air
or oxygen, the primary method for managing CNS toxicity related
oxygen exposure is to keep your PO2 at or less than 1.4 ata (work-
ing phase) or 1.6 ata (decompression/safety stop phase). However,
you must accept the risk that, under rare circumstances, CNS oxygen tox-
icity can occur at PO2s lower than 1.4/1.6 ata. Therefore, it’s prudent
to stay well within oxygen limits.
CNS toxicity is very unpredictable when a diver exceeds 1.4 - 1.6 ata
PO2. There’s not a clean time/exposure relationship between your
PO2 and the risk of a hit. Furthermore, physiology can cause sig-
nificant variability — the same diver can have no problems at an
excessively high PO2 for hours one dive, and convulse in minutes
at a lower PO2 in another. High exertion, cold water and some
drugs (CNS exciters) may make CNS toxicity more likely. Although
your risk diminishes when you drop your PO2, you can still have a
convulsion after ascending or switching to a gas with less oxygen.
Therefore, your best safeguard is to stay well within limits — there’s
generally no real dive time or decompression advantage to pushing
them.
Finally, although not available at this writing, it appears that full
face masks suitable for practical decompression in tec diving will
be available; consider using them — you’re far less likely to drown
if you should have the misfortune to convulse underwater, but the
fortune to be using a full face mask.
Pulmonary Oxygen Toxicity. Pulmonary toxicity results from long
term and repeated exposure to PO2s above .5 ata. It’s the lungs’
reaction to the elevated oxygen partial pressure and is not immedi-
ately life threatening. Signs/symptoms include lung irritation, burn-
ing sensation in the chest, coughing, and reduced vital capacity.
In recreational enriched air diving, pulmonary toxicity is highly
unlikely. Staying within no stop limits and using EANx blends with
40 percent oxygen and less, you have to dive your brains out to
get anywhere near your exposure limits. In tec diving, however,
it’s another story. Because of your dive depth, because you may
use EANx with more than 40 percent oxygen and/or pure oxy-
gen when decompressing, and because your dive duration may
go well beyond no stop limits, pulmonary toxicity becomes much

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 more likely, especially when tec diving for several days in a row.
Fortunately, it’s not difficult to manage your oxygen exposure and

ONE
avoid pulmonary toxicity.

Managing Pulmonary Oxygen Exposure.

The DSAT Oxygen Exposure Table, which you’re familiar with from
your PADI Enriched Air Diver course, is one of several variations of
the so-called “CNS clock” method for managing oxygen exposure.
The “CNS clock” is based on allocating exposure as a percentage
of the maximum of the US National Oceanic and Atmospheric
Administration (NOAA) oxygen limits. (See the Oxygen Limits
Table in the Appendix.)
The method was labeled the “CNS clock” because it was thought,
somewhat inaccurately, to manage CNS expo-
sure. Actually, it is useful, but primarily because
it manages pulmonary oxygen toxicity —
though may have some benefit in reducing CNS
risk. You’ll build upon what you learned in the
Enriched Air Diver course to extend the method-
ology in Chapter Three.
You’ll also be learning to use the Repex method
for managing pulmonary oxygen toxicity.
This method assigns oxygen dose units, called
Oxygen Tolerance Units or Oxygen Toxicity
Units (OTUs), based on your daily exposures,
and your cumulative exposure for multiple days
of diving. Although using OTUs and the “CNS
clock” at the same time is somewhat redun-
dant, doing so has a good track record and has The DSAT Oxygen Exposure Table, which
become the prevailing practice in tec diving. you’re familiar with from your PADI Enriched
Air Diver course, is one of several variations of
You’ll learn more about OTUs, how to determine
managing oxygen exposure based on allocat-
them and OTU limits in Chapter Three. ing exposure as a percentage of the maximum
of the US National Oceanic and Atmospheric
Also in Chapter Three, you’ll learn three ways Administration (NOAA) oxygen limits.
by which you track OTUs and the “CNS clock.”
One is by using formulas and tables (better) to
tally your exposure for each dive. Enriched air
dive computers also track oxygen exposure automatically (more
practical) and desk top decompression software will automatically
calculate both “CNS clock” and OTUs (very practical and simplifies
dive planning, even with a dive computer.)

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 Tec Exercise – 1.3

1. An Equivalent Air Depth is a(n) ________________ 8. (Imperial) A 100 cubic foot cylinder, working pressure
______________ you use on __________ tables when 2450 psi, has 2200 psi in it. How many cubic feet of gas
does it hold?
using enriched air nitrox with air tables. You find it
with a(n) _______________ or by looking it up on a(n) 9. The primary cause of CNS oxygen toxicity is
________________. ___________, and the primary cause of pulmonary oxy-
gen toxicity is __________.
2. The maximum recommended PO2s for technical deep a. exposure to PO2s above 1.4-1.6 ata/long term
diving are _________ ata for the bottom/working dive exposure to PO2s above .5 ata
phase, and ________ ata for the decompression phase. b. exposure to PO2s above .5 ata/long term exposure
to PO2s above 1.4-1.6 ata
3. The maximum depth you can use a gas blend during
the working part of a dive is determined by c. exposure to PO2s above .5 ata/long term exposure
a. the depth at which it reaches 1.4 ata. to PO2s above .5 ata
b. the density of the gas. d. None of the above.
c. approximately nine variables. 10. Signs and symptoms of CNS toxicity include (check all
d. the depth at which it reaches 1.6 ata. that apply):
a. convulsion c. ear ringing
4. The maximum depth you can use a gas blend during
the decompression part of a dive is determined by b. tunnel vision d. nausea
a. the depth at which it reaches 1.4 ata. 11. Signs and symptoms of pulmonary toxicity include
b. the density of the gas. (check all that apply):
c. approximately nine variables. a. lung irritation c. coughing
d. the depth at which it reaches 1.6 ata. b. frequent urination d. reduced vital capacity

12. The “CNS clock” is based on allocating exposure as a

5. To find your SAC rate you swim underwater and enter
percentage of the NOAA oxygen limits.
your ________________, ________________, and the
True False
_______________ _____________ ____________ into the
SAC rate formula. 13. OTUs are oxygen doses based on your daily exposures
and your cumulative exposure for multiple days of diving.
6. (Metric) If your working SAC rate is 19 litres per minute,
True False
how much gas supply do you need for 20 minutes at 18
metres? Answer: _____________ 14. The way you determine your OTUs and “CNS clock” is
6. (Imperial) If your working SAC rate is .68 cubic feet per with (check all that apply):
minute, how much gas supply do you need for 20 min- a. formulas.
utes at 60 feet? Answer: _____________ b. tables.
7. (Metric). You’ve estimated you need 2450 litres of gas c. dive computers (track automatically).
for a dive. Following the rule of thirds reserve, what’s d. desk top decompression software.
the total volume of that gas you should have? Answer:
_______ 15. The primary way you avoid CNS oxygen toxicity is by
a. limiting your PO2 to 1.4 ata (working phase) and
7. (Imperial). You’ve estimated you need 94 cubic feet
1.6 ata (deco phase).
of gas for a dive. Following the rule of thirds reserve,
what’s the total volume of that gas you should have? b. tracking your “CNS clock” exposure.
Answer: _______ c. tracking your OTUs.
8. (Metric) A 12 litre cylinder has 155 bar in it. How many d. All of the above.
litres of gas does it hold? _____

Check it out.
1. adjusted depth, air, formula, table. 2. 1.4 ata/1.6 ata. 3. a. 4. d. 5. depth, time, pressure you used. 6. (Metric) 1064 litres,
(Imperial) 38 cubic feet. 7. (Metric) 3675 litres, (Imperial) 141 cubic feet. 8. (Metric) 1860 litres 8. (Imperial) 89.8 cubic feet.
9. a. 10. a,b,c,d. 11. a,c, d. 12. True. 13. True. 14. a,b,c,d. 15. a.

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 Team Diving I Tec Objectives

ONE
The Team Concept Highlight or underline
One of the first things you learned as a recreational the answers to these
diver is that you dive with a buddy. And as you recall, questions as you find
you do this for reasons that include safety advantages, them:
practicality and to have more fun. 1. What is meant by
“team diving”?
Tec diving takes the buddy system to the next emphasis
level with the team diving concept. What team diving 2. What are four ben-
efits of team diving?
means is that you embrace and apply the philosophy
that tec divers work as a team, integrating each team 3. What are your
member’s needs and efforts during predive checks, meet- responsibilities as
a team member
ing equipment requirements, planning and executing
when technical div-
the dive, and other details, while pursuing a common ing?
goal. As a team, you treat the dive as a mission with
4. What is the rule
specific purpose the team pursues together with a com-
regarding aborting a
mon goal, rather than just as an “underwater visit.” technical dive?

Team Diving Benefits

There are several reasons why technical diving
embraces the team diving concept so closely. Each of
the following benefits have proved themselves again
and again:
1. Team diving has a higher likelihood of mission
success based on detailed dive planning. When
several people focus their efforts on a common goal,
it’s more likely to get done than if the same people
dive together with diffuse purpose. The more effort
and planning that goes into the single mission, the
higher the probability of success.
2. Team diving fosters preparedness and resources
for handling complex emergencies. One distinct
aspect of tec diving is that handling problems can be
Team diving integrates each team member’s
needs and efforts while pursuing a common far more complicated than in recreational diving. A
goal. As a team, you treat the dive as a mis- unified, team approach to problem prevention and
sion with specific purpose the team pursues management brings maximum resources to bear
together with a common goal, rather than
just as an “underwater visit.” when trouble rears its head — and a higher likeli-
hood of a happy outcome.
3. Team diving reduces accidents by providing a “back up brain”
for each other during predive checks and throughout the dive. You
can have multiple regulators, multiple cylinders, multiple comput-

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 ers, multiple dive tables and multiple almost everything, but you
still only have one brain. The fact is, most dive accidents don’t
result from spontaneous bad luck, but directly or indirectly from
human error. By diving in a team, you and your team mates agree
on plans and procedures, and remind each other of these by div-
ing closely together. When everyone does everything the same way
at the same time, the probability of an omission or mistake by one
team member goes way down.
4. Team diving provides the camarade-
rie that comes from facing a challenge
together. Until you’ve experienced it, you
can’t understand how common goals and
purpose will bring you and your fellow
team mates together in spirit. However,
by the end of the DSAT Tec Deep Diver or
Apprentice Tec Diver course you will — in
fact, it’s one of your goals as a student.
When you meet with your class mates next,
Until you’ve experienced it, you can’t understand how start thinking of them as team mates. To
common goals and purpose will bring you and your fel-
low team mates together in spirit.
an extent, you’ll be trusting your life to
some of them, and they to you.
Now there’s something to think about.

Team Size
You need to dive as part of a team, but a “team” can be two div-
ers (you and another diver) or 10 to 20 divers working on a project.
There are no hard “rules” or “standards” regarding team size, but
typically two to four divers compose a dive team (this doesn’t count
support divers, when present). Large teams (typically five or more
divers) usually divide into subteams to make things more manage-
able. The divers, the dive objective and other objectives may all
influence what the appropriate team size will be.
Many tec divers regard three as the optimum team size because it’s
small enough for the team mates to easily work together, yet may
simplify managing some emergencies because it provides two divers
to assist one with a problem. Nonetheless, you’ll find that teams of
two, or four or more, are common and function quite effectively.

Your Responsibilities as a Team Member

Being part of a team carries responsibilities, and that’s particularly
true in tec diving. Meeting each of these is what makes your team
possible, and what brings the benefits a team provides:
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 1. Be self sufficient, even in an emergency. You plan your dives so
you can respond to emergencies independently. Your team mates

ONE
give you additional resources and may be your Plan B if your
independent Plan A response falls short, but relying on your team
mates should not be your primary emergency response. Why?
Because when each team member stands independently, each can
lend strength and resources if things go awry. If team members rely
on each other from the start, the team’s taxing this reserve from
the start.
2. Don’t let the team carry you beyond your limits. You owe it to
yourself and your team mates to let them know where you limits
lie. A strong team can sometimes carry you well past them — but
at that point you’re no longer self sufficient, and you undermine
the team’s ability to respond if trouble arises. A constructive team
spirit is to help less experienced divers extend their limits so they
grow, but not bust limits and take them where they’re not capable
of taking care of themselves.
3. Watch your team mates as closely as you watch yourself. After
you check your gear, check their gear. After you confirm what gas
you’re breathing, confirm what gas they’re breathing. This is the
“back up brain” function. If you’re not sure about what a team
mate’s doing, point it out and ask — don’t assume your mate
knows more than you. Remember, human error is the number one
cause of dive accidents.
4. When necessary, surrender your individual preferences to team
needs. As you’ll learn, for example, there’s tremendous advantage
to team members diving with the same (or compatible) gases. You
may prefer something different on a given dive, but team unity
reduces task loading and simplifies handling emergencies — a
major benefit that you don’t want to eliminate. If you feel a team
choice compromises safety (which should be very rare) and you
can’t reach a consensus, then it’s your responsibility to respectfully
decline to dive.
5. Do not exert peer pressure and do not succumb to peer pressure.
All team members, including you, need to be confident about their
ability to make the dive. If something doesn’t sound reasonable, or
sounds beyond what you can reasonably handle at your experience
and training level, speak up! Rest assured, your team mates will
appreciate your candor and adjust the dive plan accordingly. (By
the way, if you ever feel peer pressured so strongly that it’s hard to
confront — it can happen — there’s a face-saving way out. Simply
say, “I can’t equalize.” After all, who but you really knows?)

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 Eliminating peer pressure is so important in tec diving, that there’s
actually a special safety rule for it. It originated in cave diving, and
today the entire technical diving community embraces it: Any
diver can abort any dive at any time for any reason.
Practice and honor this rule.

Tec Exercise – 1.4

Tec Exercise 1-4 3. Your responsibilities as a team member include (check

all that apply):
1. Team diving means that you apply the philosophy a. Be self sufficient, even in an emergency.
that tec divers work as a team, __________ each team
b. Don’t let the team carry you beyond your limits.
member’s needs and efforts while pursuing a common
c. Watch your team mates as closely as you watch
__________.
yourself.
2. Benefits of team diving include (check all that apply): d. Do not exert peer pressure and do not succumb
a. higher likelihood of mission success to peer pressure.
b. preparedness and resources for handling com-
plex emergencies 4. Any diver can _______ any ________ at any _______ for
any ________.
c. accident reduction by providing a “back up
brain”
d. the camaraderie that comes from facing a chal-
lenge together

Check it out:
1. integrating, goal. 2. a,b,c,d. 3. a,b,c,d. 4. abort, dive, time, reason.

Techniques and Procedures I

Okay, it’s time to start looking at the techniques and procedures
you’ll need as a Tec Deep Diver and Apprentice Tec Diver, and
that you’ll be learning and applying during the course Practical
Applications and Training Dives. You’ll start with predive checks,
followed by an overview of buoyancy control and weighting tech-
niques. Then you’ll learn about descent checks.

Predive Checks
In your Open Water Diver course, you learned that before each
dive, you make a predive safety check to be sure your gear’s in order
before hitting the water. You do the same thing in tec diving, but

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 as you may imagine, the check’s more extensive and
takes more time — appropriately so. Tec Objectives

ONE
You’ll actually learn two predive checklists in later Highlight or underline
chapters that give you details; for now, here are the the answers to these
general elements that you and questions as you find
your team mates cover: them:

• All equipment and back up 1. What general ele-

ments does a techni-
equipment — set up and func-
cal diving predive
tion. check cover?
• Gas supplies — contents, 2. How do you deter-
quantities and proper marking. mine the minimum
weight you need for a
• Decompression status monitor- technical deep dive?
ing — computers/tables, back
3. What is the primary
ups and compatibility. hazard of diving nega-
• Equipment rigging and con- tively buoyant, and
how do you manage
figuration — all secure, properly
this hazard?
located and routed, all team
members know where to find 4. What is the primary
hazard of excessive
each other’s gear.
positive buoyancy,
Get in the habit of using a pre- and how do you man-
printed checklist, such as on the age this hazard?

A tec dive begins with predive planning and TecRec Dive Planning Checklist. 5. How do you deter-
predive checks — something you’ll practice mine the minimum
many times during this course. buoyancy you need
for a technical deep
Weighting and Buoyancy dive?
You’re about to take what you learned about proper 6. What are the tech-
weighting and buoyancy in recreational diving and, niques for using a dry
for the most part, heave it out the window. Tec div- suit and BCD?
ing’s a different animal and different principles apply. 7. What is the technique
for using a redundant
Determining Minimum Weight. Looking at the
(double) BCD?
mega-kit a tec diver wears, you might ask, “Minimum
weight? That doesn’t even look like an issue.” 8. What is a descent
check and when do
But surprisingly, it can be. Although you may be quite you do it?
negatively buoyant at the start of a dive with no lead,
consider that you carry a huge gas volume compared
to recreational diving. On some dives, were you to consume almost
all your gas, you’d be 7 kg/15 lbs or more lighter than when you
started. At the end of the dive you might find yourself unable to
stay down to make a decompression or safety stop.
Therefore, you normally want to weight yourself for the worst-case

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 scenario, which would be an emergency situation of
having to maintain a decompression/safety stop at
5 metres/15 feet with nearly empty doubles. To find
this, put on all your gear (but no stage/deco cylinders)
and perform a conventional buoyancy check with 35
bar/500 psi or less in your doubles (or high capacity
single if using one). Weight yourself so you float at eye
level, or slightly sink, and you’ve set your minimum
weight for that gear configuration.
If you’re wearing heavier doubles, such as high capac-
ity steel cylinders, even with only about 35 bar/500 psi,
you may still be negatively buoyant. This is acceptable
in tec diving, and naturally, it means you don’t need
any more weight.
Hazards of Negative and Positive Buoyancy. If you’re
neutrally or negatively buoyant with near-empty cylin-
You normally want to weight yourself ders, obviously you’re going to be quite negative when
for the worst-case scenario, which
would be an emergency situation of they’re filled, and heavier and more negative still if
having to maintain a decompression/ you’re using additional stage/decompression cylinders.
safety stop at 5 metres/15 feet with In this case, you’re BCD dependent — that is, you need
nearly empty doubles. Weight yourself
so you float at eye level, or slightly
your BCD to be able to ascend.
sink, with near empty doubles and
The primary hazard of diving negatively buoyant is
without stage/deco cylinders. (With
heavy cylinders, you may still be neg- having a BCD failure that makes it effectively
atively buoyant — that’s acceptable.) impossible to ascend. As you learned earlier,
you manage this hazard by having more than
one way of regaining buoyancy control. You
may have a double bladder BCD (double wings), or a
BCD and a dry suit. However, keep in mind that for the heaviest
diving, a dry suit may not supply sufficient buoyancy (consult the
manufacturer if necessary) and you may still need a redundant
BCD. Even if it provides enough buoyancy, you have to be con-
cerned with the stress on your neck and wrist seals and the zipper,
which could fail under the stress. Excessive pressure on the neck can
cause unconsciousness due to the carotid sinus reflex.
If you’re excessively positively buoyant (underweighted or losing
your weights), the hazard is that you might not be able to make
required decompression stops, and/or have an uncontrolled ascent,
leading to very high DCI risk. You manage this risk by checking
your weight as you just learned (with near empty cylinders), and
by rigging your weights so you won’t lose them easily (such as by
using two buckles on your weight belt).

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 Determining Minimum Buoyancy. Given that
you may be quite negatively buoyant at the start

ONE
of a tec dive, having enough buoyancy is a real
issue. The minimum buoyancy you need is suf-
ficient buoyancy to float with your head comfort-
ably above the surface while wearing full doubles
and stage/decompression tanks. You choose your
BCD lift capacity with this in mind, and confirm
by checking in water shallow enough to stand in.
In determining minimum buoyancy, a reminder:
you don’t use both bladders in a double BCD at
the same time. They don’t double your lift. You
use them one at a time.

The minimum buoyancy you need is Buoyancy Control Underwater

sufficient buoyancy to float with your
head comfortably above the surface Controlling your buoyancy underwater on a tec
dive differs from on a recreational dive in many
while wearing full doubles and stage/
decompression tanks. respects. If you’re diving in a wet suit, you’ll use
your BCD. Okay, okay, duh, but one difference is
that while you should have relatively little air in
your BCD while underwater on a recreational dive, when tec diving
you’ll usually have a good bit of gas in it to offset the weight.
If you’re diving dry on a recreational
dive, you control buoyancy exclusively
with your dry suit while underwater
(except in an emergency). Not so on
a tec dive because that would be way
too much gas in your dry suit. Instead,
you will add and release air from both
your BCD and your dry suit, putting
just enough in your suit to offset suit
squeeze. This is a bit more task loading
than controlling just one device.
When tec diving you’ll usually have a good bit of gas in
During descents, one technique that your BCD to offset the weight of all your gear.
helps is to hold your BCD inflator over
your dry suit inflator so that you can
add air to both with the same hand. This leaves your right hand
free to equalize your ears, follow a line, etc. Whether diving wet or
dry, begin adding gas as soon as you start down and keep adding
in bursts as you go. Because of your weight, negative buoyancy
mounts rapidly as pressure compresses your suit and the air in your

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 BCD. If you let this get ahead of you, you
may find it hard to regain control of your
descent. (Don’t worry — you’ll practice this
in moderately shallow water until you get
the hang of it.)
If diving dry, on ascent raise your left shoul-
der and suit exhaust valve,
with the valve set to release
expanding gas automatical-
ly. That way, as you come
up you only have to release
When descending in a dry suit, hold the BCD inflator gas from your BCD manual-
over the suit inflator. This allows you to inflate both ly, while the suit takes care
with one hand — the BCD with your thumb and fore-
finger, and the dry suit with your middle finger. (No
of itself. Diving wet, you’ll
impolite gestures intended!) just have the BCD, of course,
but you may be surprised
at how much more gas you
have to release compared to a recreational dive.
When diving with redundant BCDs (double wings),
as you’ve learned, you don’t use the back up unless
the primary fails. One reason for this is that if you
were to inflate both simultaneously, the stress on
the outer bag that holds both bladders could rip it, As you ascend, vent air from both
your dry suit and BCD. This differs
causing the entire system to fail. (Oops.) This is par- from recreational dives in a dry
ticularly possible during ascent, when both bladders suit, during which you control your
could burst the outer bag before their over pressure buoyancy only using the dry suit
underwater.
valves opened.

Descent Checks
Besides predive checks, technical
divers check each other after they
get into the water. Depending upon
dive requirements, they may do
this just under the surface, or by
pausing in the 5 metre/15 foot to 6
metre/20 foot range, or at the depth
where you stage your first deco cyl-
inder, or a combination of these.
You use a descent check to look for
You use a descent check to look for gas leaks, to confirm gear gas leaks, to confirm gear operation
operation and to confirm each other’s kit. It takes only a and to confirm each other’s kit.
moment, but gives the team a pause to make sure everything’s in
It takes only a moment, but gives
order before forging onward.

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 the team a pause to make sure everything’s in order before forging
onward.

ONE
You’ll learn descent check details later in the course. For now and
in your first training dive, practice by looking over your team
mate(s) for anything that might be out of sorts.

Tec Exercise – 1.5

1. The general elements of a predive check include (check resulting in a high risk of __________.
all that apply):
5. The minimum buoyancy you need is sufficient buoy-
a. equipment set up and function
ancy to float with your ________ comfortably above
b. gas supplies — contents, quantities and marking
the surface while wearing _________ ________ and
c. equipment rigging and configuration _____/_______ _______.
d. dive conditions
6. When tec diving in a dry suit, you only add gas to the
2. If you’re properly weighted for a tec dive, generally you suit, and not the BCD, to control buoyancy underwater
should float at eye level (or be negative) with True False
a. full back cylinders and full stage/deco bottles.
7. You would use both bladders at the same time in a
b. full back cylinders and nearly empty stage/deco redundant (double wing) BCD when (check all that
bottles. apply)
c. nearly empty back cylinders and full stage/deco a. at the surface.
bottles. b. one bladder doesn’t provide enough buoyancy
d. nearly empty back cylinders and no stage/deco alone.
bottles. c. carrying stage/deco cylinders.

3. The primary hazard of diving negatively buoyant is d. Never.

have a _________ failure that makes it effectively impos- 8. A descent check is normally made just below the
sible to ____________. surface, or in the 5 metre/15 foot to 6 metre/20 foot
range, to look for gas leaks, to confirm gear operation
4. The primary hazard of excess positive buoyancy is that and to confirm each other’s rigging.
you might not be able to _______ _______ _________
True False
_________, and/or have an uncontrolled _________,

Check it out.
1. a,b,c. d is not correct because evaluating dive conditions is part of predive planning and preparation, not the check. 2. d 3.
BCD, ascend. 4. make required decompression stops, ascent, DCI. 5. head, full doubles, stage/decompression tanks. 6. False. In
tec diving, you will usually need to add gas to both the dry suit and the BCD. 7. d. 8. True.

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 Tec Objectives Emergency Procedures I
In the last section you learned some of the procedures
Highlight or underline the you’ll use routinely as a tec diver. In this section, you
answers to these questions begin learning about the many emergency procedures
as you find them:
tec divers must master. They’re similar to, but not
1. What are the emergency always identical to, recreational methods for handling
procedures for using the the same type emergency. One reason for this is that
long hose second stage
tec diving emergency pro-
to handle an out of gas
emergency? cedures arise from the fact
that ascending directly to
2. What are the emergency
the surface is usually not an
procedures for a massive
regulator free flow at option. You will practice the
depth? procedures covered here dur-
ing Training Dive One, and
3. What are the emergency
procedures for a dam- continue to practice them
aged doubles manifold throughout the course. The
at depth? idea is to be able to perform
4. What are “S-drills” and emergency skills quickly, con- The tec diving emergency procedures you’ll be learn-
when do you do them? fidentially and automatically. ing arise from the fact that ascending directly to the
surface is usually not an option.

No Gas Emergency – Long

Hose Gas Sharing
Gas sharing with your long hose is similar to alternate air source
air sharing in recreational diving. However, while this is a primary
means for handling a gas emergency in recreational diving, in
technical diving it is actually a secondary option because the victim
should always have another breathing source available. Sharing
with a team mate only comes into play when the secondary breath-
ing source doesn’t work either, or there’s some delay in deploying it.
You might need to share gas with your long hose for several rea-
sons. The victim may have planned the gas requirements poorly,
or failed to execute the gas management plan properly. A runaway
regulator or manifold leak could have drained a substantial por-
tion of the supply, and the victim exhausts the remainder with the
secondary regulator before the dive ends. There could also be an
unplanned delay in ending the dive, taxing the gas supplies avail-
able. Finally, in a no-gas emergency, sharing with your long hose is
the most immediate way you can assist a team mate. Even if team
mates have another breathing source (as they should), your long
hose solves the immediate need for gas while you sort out the prob-
lem and the options.

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 The procedure for using the long hose is:
1. Out of gas diver (receiver) signals “out of

ONE
gas.”
2. The donor passes the second stage from
the mouth to the receiver, unlooping
the hose from over the head with an
arm twist while doing so (with practice,
easier than it sounds — no worries). The
donor then switches to the short hose
secondary hanging around the neck.
If the long hose is clipped off (while
breathing from a stage/deco cylinder),
the donor jerks it off the breakaway clip
and stays on the stage/deco cylinder.
3. Abort the dive. If the receiver must
stay on the long hose, the hose length
provides versatility to maneuver as
necessary for the specific situation. If
you’re still in a no stop situation, you
ascend to the safety stop and/or surface.
On a decompression dive, you ascend
to where the receiver can switch to a
decompression cylinder.

Regulator Free Flow –

Gas Shut Down
As you recall, modern regulators usually
free flow if they fail. A minor free flow is
not usually an urgent situation (though
you want to end the dive because a small
leak can get worse), but a runaway regula-
tor will quickly deplete your precious gas.
A common reason for a free flow is poor
maintenance, however, a dislodged first
stage can also cause a runaway gas leak
between the valve and the regulator. This
usually results from impact, and is less
likely with DIN regulators. Another cause
in cold water diving is regulator freezing. When a team mate signals “out of gas,” you deploy
the long hose second stage by unlooping it from
If this happens you’ll have a lot of gas around your head in one motion. Switch to your
rush from the second stage, or from where short hose regulator while your team mate uses the
long hose.
the first stage meets the valve.

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 Follow this procedure:
1. Breathe from the unaffected regulator.
2. Reach behind you and close the valve to the free
flowing one. Having the valves all the way open
(not closed back a partial turn) reduces confusion
about which way to turn — the only direction it
goes is closed. After you close it, everything gets
quiet fast.
You should be able to do this independently. If
necessary, loosen your waist strap, undo/loosen the
You should be able to independently close crotch strap and lift the cylinders with your other
any of the valves on your manifold. If
necessary, loosen your waist back, undo or hand.
loosen the crotch strap and lift the cylin-
ders with your other hand.
3. Abort the dive.
In an actual emergency, your team mates may
assist. During the Training Dives, you’ll practice
helping each other and shutting down the valves independently,
with the emphasis on doing it by yourself.

Cylinder Isolation – Manifold Failure

If your doubles manifold fails, you have a leak that you can’t shut
down. This can happen due to severe impact, improper assembly,
gross over filling, poor maintenance, or a weakened burst disk. In
all cases, your gas is going bye-bye fast, usually with a huge noise
that sounds like a tornado trying to sneak up on you, and a cloud
of bubbles. Follow this procedure:
1. Reach back and close the isolator valve in the manifold’s center.
This will preserve the gas remaining on the unaffected side. This is
similar to a regulator valve shutdown, and again, it helps to have
the valve all the way open so there’s no question about which
way to turn. After you close it, the gas will continue to rush from
the affected side until it’s gone. Don’t reopen the isolator trying to
make it stop —you can’t.
2. Try to determine which side is leaking. Lean back and look up to
see if you can tell where the bubbles are coming from. Look at your
SPG — if it’s dropping like crazy, the leak’s on the left. If not, it’s on
the right. A team mate will probably be able to tell better than you.
3. As you abort the dive, breathe from the leaking side until the gas
is gone before switching to the conserved side.

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 Single cylinders obviously don’t have an isolator valve, and in
some areas you may have difficulty finding doubles with isolator

ONE
valves.
If you have an unidentified gas leak behind your head that you
cannot immediately solve, close the isolator immediately until
you sort out the problem. If it’s not the manifold (such as a dis-
lodged first stage), you can reopen the isolator after correcting the
problem.
As with regulator valve shutdowns,
team mates may help each other, but
your practice will focus on doing it
yourself for self sufficiency.
A note, by the way, for overhead
environment diving (if you’re quali-
fied or take it up in the future): your
left manifold valve can roll shut if it
bumps the ceiling repeatedly while you
swim. Check it periodically to be sure
it’s all the way open, and avoid ceiling
An S-drill is a safety drill in which you and your team
contact. (You learn more about these mates practice long hose gas sharing while swimming,
during courses for these activities.) valve shut downs and other emergency procedures.

S-drills
Tec divers periodically practice “S-drills” to stay prepared for
emergencies (“S” for “safety,” of course. Told you divers shorten
everything.) An S-drill is a safety drill in which you and your
team mates practice long hose gas sharing while swimming,
valve shut downs and other emergency procedures. You normally
do this in shallow water before a dive, though you may practice
them during safety/decompression stops (passes the time), or
make a separate dive just for the practice.
You perform an S-drill when:
• diving with new team mates for the first time.
• you want to practice and refresh your skills.
• your team needs to modify any emergency procedures to
address specific dive requirements.
• you and team mates need to confirm that you’re following the
same procedures.

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 Tec Exercise – 1.6

1. When sharing gas, the regulator you pass to the 3. In the event of a gas leak from a damaged doubles
receiver is manifold, you should (check all that apply):
a. whichever one is handy. a. breathe from the regulator on the affected side.
b. the long hose, which is in your mouth. b. breathe from your team mate’s long hose.
c. the long hose, which is hanging around your c. shut down the valve to the affected regulator.
neck. d. close the isolator valve.
d. the short hose, which is hanging around your
neck. 4. You perform an S-drill when (check all that apply):
a. diving with new team mates for the first time.
2. In the event of a massive regulator free flow, you
b. you want to practice and refresh your skills.
should (check all that apply):
a. switch to the unaffected regulator. c. your team needs to modify any emergency pro-
cedures to address specific dive requirements.
b. breathe from your team mate’s long hose.
d. you and your team mates need to confirm that
c. shut down the valve to the affected regulator. you’re following the same procedures.
d. close the isolator valve.

Check it out:
1. b. 2. a, c. b is not correct because you still have gas and a functioning regulator. c is not correct because closing the isolator
does not stop gas escaping the free flowing regulator. 3. a, d. b is not correct because you still have gas and two functioning
regulators. c is not correct because a regulator is not the problem. 4. a,b,c,d.

Tec Objectives
Thinking Like a Technical Diver I
Becoming a capable tec diver means learning to think
Highlight or underline the like one. Learning a way of thinking may sound like
answers to these questions a tall order, but actually, you do it all it the time, and
as you find them: you did when you became a recreational diver. It means
1. What does Hick’s Law that you learn the principles that influence how you
tell us about reaction will plan, execute and learn from every dive you make.
times in an emergency?
There may be things that you’re learning now, in this
2. What is the KISS prin-
course that you understand when and how to apply, but
ciple, and how does it
relate to technical div- not why tec divers are so adamant and inflexible about
ing? them. As you master thinking like a technical diver,
suddenly you’ll discover you understand. You’ll find
3. What is the over-riding
mission of all technical that you innately understand why tec procedures are
dives? what they are, why tec divers do what they do and it
will seem obvious. At that point, you will be a Jedi . . .
4. Why does “cutting cor-
ners” lead to technical well, something like that.
diving accidents?

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 Hick’s Law and Establishing Emergency Procedures

ONE
Question: For a given emergency situation, is it better to have lots
of possible ways to handle it, or just one or two? Many people
would say “lots of possible ways,” instinctively judging based it on
the idea that the more options you have, the more likely one will
work. Therefore, more must be better. Logical. But wrong.
Hick’s Law (1952) says:

RT = K log2 (N + 1)
where
RT = reaction time, K = a constant and N = the number of
possible choices

If that doesn’t settle it, nothing will.

Okay, okay, everyone else has to have it explained,
too. In simple terms, Hick’s Law says that the more
ways you have to respond to an emergency, the longer it
takes to react. It also says that the reaction time increas-
es substantially for each added choice.
Therefore, having lots of ways to handle the same
thing reduces how fast you’ll handle it. According to
Hick’s Law, what you want is the fewest procedural
choices possible — only as many as necessary to cover
all reasonably likely contingencies. Your reaction
speed increases because you spend less time choos-
ing what to do. Aviation, space flight, anaesthesia,
emergency medicine, and the nuclear power industry
among others have all proven this; they have found
the most effective emergency responses arise from
relatively few, standardized and practiced procedures. According to Hick’s Law, what you want
is the fewest procedural choices possible
You could really consider Hick’s Law a corollary of — only as many as necessary to cover
all reasonably likely contingencies. Your
technical diving’s ultimate principle: reaction speed increases because you
spend less time choosing what to do.
The KISS Principle
If you ever doubt what you should do in any tec div-
ing situation, chances are you won’t go wrong if you go back to the
KISS principle. KISS (polite version) stands for Keep It Super Simple.
Or in another manner of speaking, the simplest way to accomplish
anything is usually the best way.

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 Technical diving creates high mental and physical demands.
Complexity adds to these demands, so that the more complicated
the tasks required, the greater the likelihood of failure. The KISS
principle teaches you to break complex tasks into several simple
tasks to have several divers handle, to have several dive teams
handle, or to handle over two or three dives — or a combination of
these. The KISS principle challenges you to look at every part of a
dive plan and procedure and question the complex. Does it really
have to be this difficult? What can you do to simplify it?
The KISS principle also explains why the tec diving community has
evolved a fairly standardized basic rig and emergency procedures.
Standardizing reduces variables and simplifies procedures, which
conforms with Hick’s Law to reduce reaction time.
Maybe now you’re starting to understand why tec divers think like
they do.

The Mission
Technical dives tend to be mission oriented — something you’ll
spend more time on in later chapters. But no matter what you plan
to accomplish, every technical dive has an over-riding mission
that you never compromise and that supersedes everything else: To
return with all your team mates unharmed.
That may seem obvious, but as you now know, most dive accidents
result directly or indirectly from human error — and one of the
most common avoidable causes of technical diving accidents is the
error of compromising safety.
Never Compromise Safety. Recall that compared to recreational
diving, technical diving accidents arise from relatively short error
chains. You can’t cut corners prepping your gear, or planning and
executing your dive because doing so greatly increases the chance
of an accident.
Look at an example. Suppose a recreational diver goes down using
a dive computer, but (despite recommendations) neglects to take a
back up depth gauge, timer and tables. What’s the risk if the com-
puter fails? Not that high because were it to happen, the diver is
still likely to be within no stop limits, so the diver ascends, makes a
long safety stop and gets out of the water.
What about a tec diver who dives without back up tables and gaug-
es? This diver could end up paralyzed for life because a computer
failure might mean no way for the diver to determine the required

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 decompression. If circumstances separate the diver
from the rest of the team, or create a substantial dif-

ONE
ference in decompression requirements — not entirely
unlikely — that diver’s in a world of hurt.
It’s sometimes easy to rationalize “just this once” when
faced with a seemingly minor problem and missing
the dive because of it. But prudent tec divers remember
that “just this once” is the number of failures you need
without a contingency to get hurt or killed. Thinking
like a tec diver means following all safety guidelines
every time. It means you never compromise safety for
convenience, even if it means missing what would oth-
erwise be a great dive.
If you’re ever tempted to cut corners and compro-
mise safety so you can make a dive, ask yourself this:
“What will I find, see or do on this dive that would be
worth dying for?”

Thinking like a tec diver means following all safety guide-

lines every time. It means you never compromise safety for
convenience, even if it means missing what would otherwise
be a great dive. If you’re ever tempted to cut corners and
compromise safety so you can make a dive, ask yourself this:
“What will I find, see or do on this dive that would be worth
dying for?”

Tec Exercise – 1.7

1. Hick’s Law tells us that (check all that apply): 3. The overriding mission on all dives is to ________
a. the more ways you have to respond to an emer- __________ _______ ________ ________ _________
gency, the better. __________.
b. the more response choices you have, the slower 4. “Cutting corners” can lead to technical diving acci-
your reaction time. dents
c. you want the fewest response possible choices to a. because it doesn’t save any time.
cover all reasonable possibilities.
b. because in tec diving, accidents arise from rela-
d. None of the above. tively short error chains.
c. only rarely.
2. KISS stands for ____________ ________ ____________,
___________. That is, the _____________ way to d. None of the above.
accomplish anything is the best way.

Check it out:
1. b, c. 2. Keep It Super Simple, simplest. 3. return with all your team mates unharmed. 4. b.

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 Performance Preview:
Objectives Practical Application One
Practical Application One develops your skills in gear
To successfully complete this
Practical Application, you rigging, and begins establishing team diving principles
will be able to: — team thinking and team spirit. Your instructor will
assign teams and have teams work together to config-
1. Working within your
assigned team, rig your ure their rigs according to the standardized technical
gear so that the equip- rig methods and principles you’ve learned, with spe-
ment of all team members cific adaptations and requirements to meet local envi-
conforms with the stan- ronmental requirements.
dardized technical rig pre-
viously learned, and with Working as a team, refer back to the Equipment I sec-
any environment-specific tion, and any example rigs your instructor has on
requirements provided by display. Your goal is that everyone on your team has a
the instructor.
rig set up so that it satisfies the diver, the team and the
instructor.

Preview: Training Dive One

Performance Objectives

To successfully complete this training dive, simulated free flow.

the you will be able to:
6. Within 30 seconds, independently close
1. Working in a team, assemble and inspect the isolator tank valve in response to a
the basic technical diving rig following simulated manifold leak. (Simulated clos-
the previously described rigging philoso- ing is permitted if performing the skill
phy and to meet individual/environmen- with a high capacity single.)
tal needs.
7. Respond to a simulated out of gas emer-
2. Demonstrate how to determine the gency by signaling a team mate, switch-
proper weight required for the dive. ing to the team mate’s long hose second
stage, then swimming 30 metres/100
3. Demonstrate neutral buoyancy while
feet using the long hose regulator and
wearing the basic technical dive rig
maintaining contact with the team mate.
underwater in water too deep in which
to stand by hovering for 1 minute with- 8. Respond to a team mate’s simulated out
out sculling or kicking. of gas emergency by, on signal, provid-
ing the team mate with the long hose
4. Within 30 seconds, independently close
second stage, switching to the short
the tank valve to a regulator that is expe-
hose secondary, then swimming 30
riencing a simulated freeflow.
metres/100 feet as the team mate uses
5. Assist a team mate by closing the correct the long hose regulator, maintaining
valve to a regulator that is experiencing a contact.

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 Predive briefing and gearing up

ONE
Training Dive One
Entry
Weight Check
Descent
Descent check
Neutral buoyancy — hovering for 1 minute, no sculling or kicking
Regulator free flow — valve shutdown independently, within 30 seconds
Regulator free flow — team mate assist
Manifold leak — isolator shutdown independently within 30 seconds
Manifold leak — team mate assists
Out of gas — use long hose as receiver, swim horizontally 30 m/100 ft
Out of gas — use long hose as donor, swim horizontally 30 m/100 ft
Free time for practice and experience
Ascent
Recheck weight with near-empty cylinders
Exit

Post Dive
Performance review
Disassemble and stow equipment
Log dive for instructor signature
Assignments

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 Plans must be simple and flexible. Actually they

TWO
only form a datum plane from which you build as necessity
directs or opportunity offers. They should be made by the people
who are going to execute them.

— US Army General George S. Patton Jr.

1885-1945

C
hapter One established the foundation you
need as a Tec Deep Diver or Apprentice Tec
Diver. Chapter Two is the framework stand-
ing on that foundation; it takes what you’ve
learned and begins applying something on
which to build your future reference and growth as a tec
diver. Like Chapter One, it’s not a short chapter either,
and — bad news — sorry, it doesn’t have as many pictures
(though the margins are

Chapter TWO: The Framework just as wide.)

In Chapter Two, you
continue learning about tec diving equipment, especially
some items you’ll need for decompression or extended no
stop dives. Then you’ll get into gas planning again, and
this time you’re going in deep. You’ll learn the basics for
planning a hang (decompression) dive, and practice deter-
mining your gas supply requirements for a multiple depth
dive. After that you get a math-break and head into phi-
losophy, with some more on thinking like a technical diver.
Then team diving part two goes way into gas handling and
dive planning, so you get to learn two new acronyms that
guide you through the tec planning process.
Building upon that comes more on techniques and proce-
dures, this time getting you going on deco/stage cylinder

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 handling. In these procedures, you get to learn . . . yes, a third acro-
nym (Three in one chapter? Sorry, can’t be helped.) That leads into
some more emergency procedures, among which, you’ll be glad to
learn, there are no more new acronyms. The chapter finishes up
with an overview of Practical Application Two and Training Dives
Two and Three.

Equipment II
Tec Objectives
Stage and Decompression Bottles
Highlight or underline the (Cylinders)
answers to these questions
as you find them: Tank, bottle, cylinder. They’re all names divers have
stuck on scuba cylinders and they all basically mean
1. What’s the difference
between a stage bottle
the same thing so we use them interchangeably. The
(cylinder) and decompres- most “technically correct” term is “cylinder.” But
sion bottle (cylinder)? you’ll hear people call your tanks “bottles” instead
2. How do you set up a
of “cylinders” all the time.
stage bottle (cylinder) Similarly, you’ll hear “stage bottle” and “decompres-
or decompression bottle
sion bottle” used interchangeably, although there is
(cylinder)?
a difference: stage bottles extend the working part
3. What is the advantage of of your dive, whereas deco bottles are cylinders with
a stage or decompression
enriched air or oxygen for decompression. Both are
bottle (cylinder) clip con-
nection that you can cut? worn on the side under the arm, clipped at the waist
and on the chest, so you can remove and replace
4. Why might you need a lift
them as necessary. Since they’re rigged the same and
bag and reel on a techni-
cal deep dive? carried the same way, they’re often lumped together
— in fact, throughout the Tec Deep Diver Manual you
5. What are suitable lift bags
see references to “stage/deco cylinders” when discuss-
and reels for technical
deep diving, and where ing handling issues that are the same, and it doesn’t
do you secure them on matter whether you’re using the tanks to extend
your rig? your range or for decompression. You’ll learn about
6. What makes a suitable using both during the course.
spare mask for technical Now to make terminology really interesting, to
deep diving, and where
do you carry it on your
“stage” something is to leave it for later retrieval
rig? and use, usually a cylinder. Thus, you can stage
stage cylinders, but you can also stage deco cylin-
7. What are the guidelines
regarding material and
ders. In fact, you’re more likely to stage a deco cylin-
equipment compatibility der than to stage a stage cylinder.
using enriched air and
Stage/Deco Cylinder Configuration. The typi-
oxygen?
cal stage/deco cylinder has a nylon rope or strap
approximately 46 cm/18 in (more or less to indi-
vidual needs) running from under the valve open-

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 ing from the neck down to a band
around cylinder, with a clip at each
end. The rope/strap serves as han-
dling strap underwater, and the
clips secure the cylinder at the hip
and chest D-rings. You may adjust
these somewhat — some divers pre-
fer the bottom clip under the valve
knob instead of under the valve

TWO
face.
The regulator has a second stage
and SPG only, with the hoses tucked
You’ll hear “stage bottle” and “decompression bottle” used inter- under inner tubing, bungee or sur-
changeably, although there is a difference: stage bottles extend the gical tubing stretched around the
working part of your dive, whereas deco bottles are cylinders with
enriched air or oxygen for decompression. cylinder. You tuck the hoses so the
second stage deploys with a single
pull. The second stage also has a breakaway mount clip so you
can secure it and avoid pulling it out unintentionally. The short
hose SPG, bent up and pull-tied to the first stage is popular with
many tec divers because it effectively leaves only the second stage
hose to deal with. Deco cylinder regulators may have mouth blocks
or mouth guards — you’ll learn more about these in a bit. Fully set
up and ready to go, a stage/deco cylinder should be a
compact “package” that you can handle easily without
anything dangling or dragging.
Suitable cylinders for stage/deco cylinders are those
that are nearly neutral for easy handling. Avoid those
that are substantially negative because they’re awk-
ward to handle. An exception is a cylinder used for
oxygen that you’ll stage and retrieve for decompres-
sion at 6 metres/20 feet. In this case, some divers like
the added weight to help restore the weight they’ve lost
through gas consumption during the dive.
Stage/deco bottle clips attach to the cylinder via a rope
or nylon strap so that you can cut the tank away if you
need to in an emergency, or in case the clip jams (it
happens) and there’s no other way to get out of it. This
is particularly popular for wreck or cave diving because
you can’t cut your way out of all metal connections.
A few tec divers use double-ended clips with all metal Oxygen cylinder set up as a decom-
connections because it’s highly unlikely that both ends pression bottle package. Note the
double ended clip used to secure the
would jam at the same time.
cylinder at the hip.

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 You wear single stage/deco
cylinders on the left. You
may wear multiple cylinders
on both sides, or all on the
left (balance isn’t an issue if
you’re using near-neutral cyl-
inders). If you wear a cylinder
on the right, be sure it doesn’t
Many tec divers prefer a strap on their trap your long hose — the
stage/deco bottles, which makes handling
hose must be below the hip
easier and makes it possible to cut away
the cylinder if necessary. D-ring and clip. A common
configuration for wearing
deco cylinders on both sides is
to always wear your oxygen cylinder on the
right (left-lean, right-rich).
You may wear multiple cylinders on both
When scootering (which you won’t get into sides, or all on the left.
during this course), you usually wear all cyl-
inders on your left so the prop wash can aim
under your right arm. Many divers prefer
to wear all stage/deco cylinders on the left,
scootering or not, to keep habits the same
and to avoid long hose issues.
During a decompression/safety stop, you
can also clip cylinders you’re done using to
your hip by the upper clip. Although this
looks awkward, it gets them out of the way
and they trail easily behind you when you
swim.

Lift Bag and Reel

When making a deep dive in open water, During a decompression/safety stop, you can
it’s possible to find yourself away from the also clip cylinders you’re done using to your
hip by the upper clip. Although this looks awk-
anchor line or your planned ascent line ward, it gets them out of the way and they
area. Sometimes it’s not feasible to return trail easily behind you when you swim.
to a particular point to begin your ascent.
In either case, you deploy a lift bag on your
emergency reel.
The lift bag and line provide reference to ascend along, making it
easier to maintain your decompression or safety stops. It also marks
your location for the boat and support team so they know where
you are.

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 A suitable lift bag is brightly colored, with 45
kg/100 lbs or more lift preferred. Write your
name in large letters on the bag so surface
support can identify you. You can also get
bright colored, elongated bags that jut well
above the surface and double as inflatable
signal tubes. Different areas like to use differ-
ent colors, but experience shows that the best
color is marine yellow. It stands out better

TWO
than white (especially when the wind kicks up
white caps) and it’s more visible in dimmer
light than is red.
Lift bag options and protocols vary depend-
ing on the local conditions and requirements.
Sometimes tec divers carry two bags — one
of a different color that signals for assistance
from the support crew topside. Different teams
may have different colors for easy identifica-
A suitable lift bag is brightly colored, with
45 kg/100 lbs or more lift preferred. tion. In some environments, such as deep sink
holes, you might not need
a lift bag at all (you’ll prac-
tice using one as part of this
course regardless of the envi-
ronment you train in).
An appropriate reel is com-
pact with ample nylon line to
reach the surface. Once inflat-
ed, your bag screams upward,
so your reel needs to be able
to spin smoothly and rapidly,
yet allow you to put a bit of
drag and control on it. The
An appropriate reel is compact with ample
nylon line to reach the surface. Once most common lift bag reels
inflated, your bag screams upward, so your are those used for wreck and
reel needs to be able to spin smoothly and cave penetration. Some divers
rapidly, yet allow you to put a bit of drag
and control on it.
carry two reels in tandem, in
case one jams.
You carry the lift bag rolled
up and slung from your harness in the small of You carry the lift bag rolled up and slung
your back, held by two pieces of bungee or surgical from your harness in the small of your back,
held by two pieces of bungee or surgical
tubing. This keeps it secure, but completely out of tubing. This keeps it secure, but completely
the way and easy to deploy when you need it. out of the way and easy to deploy when you
need it.

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 Your reel clips to your right hip D-ring, as you
already learned. Putting it there keeps it acces-
sible and out of the way, while helping keep
your long hose in place without trapping it.

Spare Mask
It’s rare to get your mask knocked off, and
even then it’s usually your own fault for fol-
lowing too close to your team mate’s fin tips.
It’s rarer still to lose your mask and not be
able to relocate it. But were it to happen on a
tec dive with a deco obligation,
you’d have to rely on a team
mate to take you through your
decompression because you
wouldn’t be able to read your
tables and gauges. And if you’d
somehow separated from the
When worn on the hip, your reel holds the
team then, well, big problems long hose in place.
— though a computer that
provides an audio cue if you
ascend above your stop depth can make it feasible
to “listen” your way through your decompression.
With this in mind many tec divers carry a spare
mask. The spare mask isn’t considered manda-
tory, but it doesn’t take up much space, and it’s an
especially good idea for dives with a higher than
usual potential for team separation. A suitable
spare mask is as small and compact as possible. The
usual carrying place is in a compact harness pocket
A suitable spare mask is as small and com- on the waist band all the way back, behind the
pact as possible. The usual carrying place
waist D-rings. Some divers carry a back up mask in
is in a compact harness pocket on the
waist band all the way back, behind the a suit thigh pocket.
waist D-rings.

Oxygen Compatibility Review

The PADI Enriched Air Diver course taught you the basics about
considerations for gas blends with more than 21 percent oxygen.
As you recall, you need to follow protocols regarding materials,
cleaning and handling to avoid fire and/or explosion hazard. Fire
requires fuel, heat and oxygen — remove one of these and you

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 won’t have fire or explosion. Since oxygen’s a given, the following
oxygen compatibility issues exist to eliminate fuel and heat from
the equation:
1. The standard for the dive community is that any equipment
(regulator, valve, cylinder) that will be exposed to more than 40
percent oxygen at any time (including during blending) must be
rated for oxygen service. Oxygen service means that it is oxygen
clean — free of contaminants, and that it is oxygen compatible —
made from materials that don’t combust easily in oxygen. Some

TWO
dive community members, and some areas by law, require oxygen
service rating for any contact with more than about 22 percent
oxygen.
2. Follow manufacturer recommendations regarding the use of their
equipment with air, enriched air or oxygen. Some manufacturers
require oxygen service for any enriched air application, whereas
others limit the maximum oxygen percent you may use their gear
with. This may create some challenges and you may have to make
some choices — see the sidebar “Manufacturer Warranties and
Hyperoxic Gases.”
3. If you expose oxygen service equipment to gases that are not
oxygen clean, or that have other contaminants, the equipment is
no longer oxygen clean and loses its oxygen service rating until
recleaned. An example of this is using an oxygen clean/service
regulator on a standard air cylinder. Normal Grade E breathing
air is not considered oxygen compatible, and the regulator would
be considered contaminated and must be recleaned to again meet
oxygen service standards. Similarly, if you fill an oxygen service
rated cylinder from a standard air source, the cylinder loses its oxy-
gen service rating. (To maintain the oxygen service standard, you
need to fill the cylinder with oxygen compatible air, such as in the
US, Grade E Modified, or Grade J).
4. Leave enriched air cylinder content decals and tags in place for
the blender to remove. This allows the blender to confirm that the
cylinder was not refilled from a non oxygen clean source. If there’s
any question about this, the blender will require cylinder and valve
recleaning before filling.
5. To minimize heat of compression (which can be high enough
to start a fire), open cylinder valves slowly and allow equipment to
pressurize slowly when using enriched air and oxygen.
6. Protect oxygen service equipment from contamination. Leave it
bagged or otherwise sealed against the environment until it’s need-
ed. Rinse and stow it as soon as possible when you’re done with it,

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 and at all times, keep it away from areas or exhaust that might
have contaminants. If in doubt about possible contamination,
assume contamination and have the item recleaned by your PADI
Dive Center or Resort.
7. The general guideline is to have oxygen service equipment
recleaned annually. That works out because that’s the same inter-
val for most regulator overhauls and tank/valve visual inspections.
8. Violating guidelines regarding oxygen service and oxygen
compatibility carries a severe risk of injury and/or property dam-
age from fire and/or explosion. Follow the guidelines, and you’re
unlikely to ever have an incident related to oxygen compatibility.

Tec Exercise – 2.1

1. A stage bottle is used ________________ and a decom- 4. You carry a lift bag and reel to provide a ___________ to
pression bottle is used __________. ascend along and to _________ __________ ________ for
a. for decompression, for decompression the boat and support team.

b. to extend the bottom time, for decompression 5. A suitable lift bag is _____________ colored, with
c. to extend decompression or to extend bottom _________ lift preferred. You carry it in the _________
time, to extend decompression or to extend bottom ___ _________ __________ held by two pieces of bungee
time or surgical tubing.
d. None of the above.
6. A suitable spare mask (check all that apply):
2. A stage or decompression cylinder is set up with a regu- a. is small and compact.
lator that has a primary and alternate second stage. b. rides in a small pocket behind the hip D-ring.
True False c. is recommended, but not considered mandatory.
3. The advantage of a stage/deco cylinder clip connection d. must be bright orange for safety.
that you can cut is (check all that apply):
a. that’s the usual method for removing the cylinder. 7. Violating oxygen service and compatibility guidelines
risks severe __________ and/or property _________ from
b. it’s the fastest way to add a new clip.
_________ and/or ____________.
c. it permits your buddy to remove the cylinder if
you’re unconscious.
d. None of the above.

Check it out:
1. b. 2. False. The regulator has one second stage. 3. d. Cutting allows you to remove the cylinder if the clip jams. 4. reference,
mark your location. 5. brightly, 45 kg/100 lbs, small of your back 6. a,b, c. 7. injury, damage, fire, explosion.

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 Manufacturer Warranties and Hyperoxic Gases

A
s you realize by now, from the risk of fire. That’s why, using properly cleaned and com-
in the DSAT Tec Deep as you’ve learned, any high patible equipment, not using
Diver and Apprentice pressure device coming in con- oxygen is a far greater risk than
Tec Diver courses, you’re learn- tact with a gas with more than using it. In fact, while plenty of
ing to use enriched air nitrox 40 percent oxygen (or less than divers have been bent over the
with more than 40 percent 40 percent if specified by the years, as of this writing only one

TWO
oxygen and/or pure oxygen to manufacturer) must be cleaned has been seriously injured as a
extend no stop time and benefit and dedicated for use with pure result of an oxygen fire using a
decompression. oxygen. hyperoxic gas in a technical scuba
diving context. And that is in
Not only are these hyperoxic That’s easy to say, but not as
the context of tens of thousands
gases recommended, their use easily done.
of dives (at least) made with such
verges on the essential for de-
At this writing, virtually no mixtures over the past decade.
compression after long, deep
equipment manufacturer in the
dives. The use of higher oxygen In the end the choice will be
dive industry warrants the use
goes probably lessens the risk of yours. If you decide to stick with
of their equipment with pure
decompression sickness, because the strict manufacturer’s guide-
oxygen. Some specifically warn
it is generally believed that for a lines for your regulators, tanks,
against using their equipment
given a decompression model, a valves, and SPGs, you may have
with enriched air nitrox mix-
schedule requiring shorter stops to choose decompression gases
tures containing greater than
is more reliable than a schedule with no more than 40 percent
40 percent oxygen. Nor should
requiring longer stops. Without oxygen, at least until manufac-
you consider the use of any
the high oxygen, you’d face turers change their policies. But
specific equipment by a diver or
impractically long decompres- if so, you must then be willing
instructor, or the appearance of
sion stops. Therefore, when a to accept the risks attendant to
such use in a published photo
diver can get out of the water the lengthier decompression
(including those in this manual)
quicker (accelerated decompres- times involved.
or video as an implied warranty

M
sion), it reduces the exposure to
of such use by the manu- ost of the technical div-
others risks as diverse as marine
facturer, the diver or instructor, ing community believes
predators, hypothermia, get-
or the publisher. Yet, you will that, the manufacturer’s
ting separated from the boat in
still learn in this course to use warnings notwithstanding, you
strong currents, and so on.
proper oxygen service equip- are better off in technical diving
Technical diving is undoubt- ment with hyperoxic gases to use oxygen and other hyper-
edly safer with the use of high including pure oxygen. oxic mixes than not. The risk of
oxygen gases than it would be fire and explosion is real and is,
Basically it comes down to
without them, which is why it yet again, another risk you must
balancing the risks: the risk of
is a standard practice in the tec personally assume before get-
getting seriously hurt or killed
diving community. Using hyper- ting involved in technical diving.
due to decompression sickness
oxic gases, however, is not with- To manage and minimize that
against the risk of getting seri-
out some risk and controversy. risk, be certain that any equip-
ously hurt or killed due to fire
Outside of issues you’ve learned ment you will use with a gas
or explosion. Most tec divers
related to central nervous sys- with more than 40 percent oxy-
believe – and accident data
tem and pulmonary oxygen tox- gen has been serviced for that
support – that provided you’re
icity, the greatest hazard comes use by a qualified professional.

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 Tec Objectives
Gas Planning II
Highlight or underline the
In the last chapter you learned about comput-
answers to these questions as
you find them: ing your gas volume requirements and reviewed
the issues surrounding oxygen toxicity. Now you’ll
1. How do you determine
required decompression broaden your dive planning skills by applying these
stops using a single gas principles to tec diving no stop dive time and decom-
computer or tables? pression.
2. How do you use switches to
enriched air or oxygen to
make decompression stops Introduction to Decompression Stop and
or safety stops more conser-
vative when using a single Gas Switch, Extended No Stop Diving
gas computer or single gas As you know already, tec diving frequently requires
tables? decompression stops due to the depth and/or dura-
3. What is accelerated decom- tion of your dive. You make the mandatory stops
pression? in stages as you ascend so excess dissolved nitrogen
4. What is a gas-switch extend- diffuses out of your body tissues without substantial
ed no stop dive? bubble formation and DCS. You need to be able to
5. What is your EAD when determine the required stops, how to maximize their
breathing pure oxy- effectiveness, and
gen? how (when feasi-
6. What is an END, and ble) to accomplish
what are the two different your dives without
assumptions it can be based mandatory decom-
on? pression.
7. Why do you assume your You’ll learn sev-
END does not change when
eral options for
using enriched air as com-
pared to air? determining your
decompression
8. How do you normally deter-
requirements. The
mine the “ideal” enriched
air for a particular depth? first and simplest Tec diving frequently requires decompression stops due to the
is to use a single depth and/or duration of your dive. You make the mandatory
9. How do you determine stops in stages as you ascend so excess dissolved nitrogen
gas dive computer
your gas supply and reserve diffuses out of your body tissues without substantial bubble
requirements for a multiple (air or enriched formation and DCS.
depth dive (including dives air), or dive table.
with decompression or safe- The “single gas”
ty stops)? reference simply means that the computer or table
10. What is “desk top decom- calculates your decompression based on the idea that
pression software,” and the diver uses the same gas while decompressing as
what are the benefits and while on the bottom.
risks of using it?
The vast majority of currently available dive comput-
ers will calculate decompression, though they vary

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 in the information they provide and the decompression
range they cover. Check the manufacturer literature for
specifics. Though you’ll probably use your computer,
you can also use any of several published decompres-
sion tables, such as the US Navy Standard Air Tables
or Canada’s DCIEM air tables. These tables specify the
depths and durations for stops for given depth and
time combinations. If you don’t have two dive comput-
ers, you can use waterproof (laminated, for example)

TWO
tables along with a timer and depth gauge for back up.
You can also use the tables to help you plan your gas
requirements with your computer. (Later in this course,
you’ll learn about using desktop decompression soft-
ware to generate tables.) For maximum reliability, when
planning your dives,you want to use tables and models
that are within the limits of known and established test
data. If you don’t have two dive computers,
you can use waterproof (laminated,
To determine your required decompression stops, you for example) tables along with a
simply follow your computer or the table. A computer timer and depth gauge for back up.
You can also use the tables to help
will usually tell you how long you have at each stop, you plan your gas requirements with
and when it’s okay to ascend to the next stop; some will your computer.
also show your total deco time remaining. The table
simply lists stops and times — you ascend to the deepest
stop depth, wait the time indicated, ascend to the next and do the
same, and so on.
Because your computer or tables assume you’re decompressing
using the same gas blend that you used on the bottom, it’s easy to
make your decompression more conservative. Upon ascending to
a depth shallow enough to avoid oxygen toxicity, you switch to a
higher oxygen EANx (or even pure oxygen in some cases) in a deco
cylinder. This allows the nitrogen to dissolve from your body more
rapidly than your computer or tables account for.
You complete your decompression using the higher oxygen gas,
resulting in a very conservative decompression. Not only is this
simple, but it’s advantageous when using some tables (like the USN
tables) designed for military or commercial divers that are not as
inherently conservative as computers and models presently devel-
oped for sport divers. Similarly, when you make technical no stop
dives, you can switch to a higher oxygen EANx, or pure oxygen, to
make your safety stop extra conservative. But, remember that after
switching, your computer doesn’t “know” and its oxygen exposure
tracking (if it does so) won’t be accurate. You’ll need to calculate
your oxygen exposure manually (more about this later).

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 Here’s an example of how you might make such a
dive: You dive to 42 metres/140 feet using EANx24
with an enriched air computer. Upon ascent, your
computer or table requires you to stop at 9 metres/30
feet, 6 metres/20 feet and 3 metres/10 feet. You com-
plete your stop at 9 metres/30 feet using EANx24 as
your back gas (the gas in your doubles) and then you
ascend to 6 metres/20 feet and switch to 100 percent
oxygen (recall that 6 metres/20 feet is the deepest you
can use pure oxygen, PO2 1.6 ata) and finish decom-
pression with it following your computer or table.
Accelerated Decompression and Gas-Switch, Extended
No Stop Dives. Because switching to higher oxygen
EANx and/or pure oxygen speeds nitrogen release,
Because your computer or tables assume rather than “pad” your decompression to make it
you’re decompressing using the same gas more conservative, you can shorten your required stop
blend that you used on the bottom, it’s
easy to make your decompression more times by using special multiple gas computers or cus-
conservative. Upon ascending to a depth tom dive tables that will calculate the gas switch. This
shallow enough to avoid oxygen toxicity, is called accelerated decompression, which you’ll learn
you switch to a higher oxygen EANx in a
deco cylinder.
more about further into the course.
Similarly, you know that a multilevel profile extends
your no stop dive time by giving your credit for
slower nitrogen uptake as you ascend. If you ascend and switch to
a higher oxygen blend in a stage bottle, your no stop time goes
through the roof — you can make incredibly long dives without ever
entering deco, and since you’re using a stage bottle, you have the
gas supply to make it possible. You’ll learn more about planning
gas-switch, extended no stop dives later; qualifying to make these
dives is one of the primary benefits of the Apprentice Tec Diver cer-
tification.

Equivalent Air Depths (Continued) and Equivalent

Narcotic Depths
The last chapter reviewed Equivalent Air Depths (EADs) with
enriched air nitrox, so let’s go one more step and figure out the EAD
for 100 percent oxygen. No matter what your depth (presumably
6 metres/20 feet or shallower to prevent oxygen toxicity) the EAD
always equals -10 metres/-33 feet. This is because the PN2 (partial
pressure of nitrogen) is 0, lower than air at the surface (even at
altitude). The mathematical result is a constant negative depth. So,
using pure oxygen underwater at any depth, nitrogen leaves your
body faster than if you were at the surface breathing air.

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 This is not simply a mathematical curiosity, but the reason why
oxygen decompression is such a big deal for tek divers. For one, it
is the fastest way to get rid of excess nitrogen (or other inert gases).
For another, it gives you flexibility in choosing your decompression
depth. You should never be deeper than 6 metres/20 feet using pure
oxygen, and you should never be shallower than the stop depth
indicated by your table or computer. But, you can be deeper than
the indicated stop depth without affecting how fast you release
nitrogen, and this is only true when using pure oxygen. Using air

TWO
or enriched air, being deeper than the indicated depth slows your
nitrogen release.
For instance, suppose you’ve reached 6 metres/20 feet and switched
to oxygen to finish your decompression. After sufficient time, your
dive tables now indicate that your next stop is 3 metres/10 feet,
but there’s a pretty good swell at the surface. Instead of going to 3
metres/10 feet, you ascend only to 5 metres/15 feet to stay below
the waves, while reducing your PO2 somewhat. Or, suppose there’s
something you can hang onto at 6 metres/20 feet for a nice, restful
decompression, but nothing like that any shallower. Using oxygen
you can just stay put to finish your decompression. (Of course,
when you’re using a single gas dive computer, it will increase your
decompression time since it thinks you’re staying deep and using
your back gas).
Equivalent Narcotic Depth (END). Equivalent Narcotic Depth calcu-
lates the expected narcosis for a gas mix with an equivalent depth
as if breathing air. For instance, if a gas blend is said to have an
END of 30 metres/100 feet at 60 metres/200 feet, it means that at
60 metres/200 feet breathing that blend you’d be subject to the
same narcosis as if breathing air at 30 metres/100 feet.
At one time, it was common to calculate ENDs for enriched air
nitrox, but today ENDs are really only relevant to gas blends with
non narcotic helium (using helium blends is beyond the scope of
this course). The reason is that the old assumption was that oxygen
is not narcotic, and therefore EANx, with less nitrogen than air has,
would be less narcotic than air.
More recently, however, it appears that oxygen is probably just
as narcotic as nitrogen (or even slightly more so). Therefore, you
want to assume your END does not change when comparing air to
EANx. (Some desktop decompression software will calculate ENDs
for EANx; disregard these shallower ENDs and assume that EANx is
just as narcotic as air.)

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 Ideal Enriched Air for a Particular Depth
For most dives, the “ideal” enriched air blend for a planned par-
ticular depth is the one with the highest permissible oxygen con-
tent within oxygen limits. The highest oxygen blend gives you the
most no stop time/least deco time. For the majority of dives, this is
the EANx with its 1.4 maximum depth at or just deeper than the
planned depth. The easiest way to find the ideal depth is to use the
Maximum Depth Table in the appendix.
For example, what’s the “ideal” EANx for a dive to 40 metres/130
feet? In the table’s 1.4 column, find 40 (metric) or 132 (imperial)
opposite 28 percent, indicating EANx28 is the “ideal” blend.

METRIC IMPERIAL

MAXIMUM DEPTHS IN MAXIMUM DEPTHS IN

METRES OF SEAWATER FEET OF SEAWATER
BLEND @1.4 @1.6 BLEND @1.4 @1.6
21% 57 66 21% 187 218
22% 54 63 22% 177 207
23% 51 60 23% 168 197
24% 48 57 24% 160 187
25% 46 54 25% 152 178
26% 44 52 26% 145 170
27% 42 49 27% 138 163
28% 40 47 28% 132 156
29% 38 45 29% 126 149
30% 37 43 30% 121 143
31% 35 42 31% 116 137
32% 34 40 32% 111 132
33% 32 38 33% 107 127

Of course, the “ideal” isn’t always the most practical. For instance,
you may find ready access to a blend with less oxygen but not the
“ideal” blend, with no meaningful difference in how it affects your
no stop or decompression time. And, going with a bit less oxygen
than the “ideal” blend gives you some margin for error; you can
accidentally descend a bit past your planned depth without exceed-
ing 1.4 ata. If you’ve made several dives, your oxygen exposure
(OTUs/”CNS clock”) may require a lower PO2 than 1.4 to permit the
bottom time you want.

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 Determining Gas Supply and Reserve Requirements for
Multiple Depths and Decompression Stops
In the last chapter you learned how to estimate your gas requirements
and reserve requirement for a single depth and time based on your
Surface Air Consumption (SAC) rate. Now let’s look at the bigger pic-
ture: your gas and reserve requirements for multiple depths, your ascent
and decompression stops when using more than one gas blend. It’s a bit
of number crunching, but not difficult.

TWO
Conversion Factors. To simplify using your SAC rate, you can use a
conversion factor for a given depth off the Conversion Factor Table in
the Appendix. Your required gas estimate then becomes: SAC x minutes
x conversion factor. If there’s no conversion factor for the depth you
need, round to the next greater depth. (For the mathematically curious,
the conversion factor is simply the absolute pressure in atmospheres –
Metric: (D in metres +10)/10; Imperial: (D in feet +33)/33.)
For example, if your SAC were 24 l/min, how much gas would you
consume in 15 minutes at 30 metres? On the Conversion Factor Table
find that the factor for 30 metres is 4.0. Then: 24 l/min x 15 min x 4.0
= 1440 litres. In the imperial system, suppose your SAC were .7 cf/min.
How much gas would you consume in 15 minutes at 100 feet? On the
Conversion Factor Table find the factor for 100 feet is 4.0.
Then: .7 cf/min x 15 min x 4.0 = 42 cubic feet.

SAC CONVERSION FACTORS

Multiply your SAC rate by the factor to determine your gas comsumption rate at depth.

Metric Imperial
Depth (m) Conversion Factor Depth (ft) Conversion Factor
3 1.3 10 1.3
5 1.5 15 1.5
6 1.6 20 1.6
9 1.9 30 1.9
12 2.2 40 2.2
15 2.5 50 2.5
18 2.8 60 2.8
21 3.1 70 3.1
24 3.4 80 3.4
27 3.7 90 3.7
30 4.0 100 4.0
33 4.3 110 4.3
36 4.6 120 4.6
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 To estimate your entire dive gas supply, it’s simply a matter of
doing this for every depth and decompression stop, and your
ascent. The TecRec Dive Planning Slate organizes your depth, con-
version factor, time and blends to help you with planning. It also
lets you record other planning information that you’ll learn about
later. In sorting out the depths and times:
• Treat the descent time as though it were spent at the first depth.
• Your ascent depth is the midpoint between the bottom and the
first stop. To find this, subtract the first stop depth from the bot-
tom depth, divide that by two and then add it to the stop depth.
The ascent time is the time from the bottom depth to the first
stop; divide the distance from the bottom to the first stop by the
ascent rate to get the time. (You typically round the time to the
closest whole minute.)
Example: You’re diving at 30 metres/100 feet and your first stop
is at 12 metres/40 feet. Your ascent depth is 21 metres (30-12 =
18, 18 ÷ 2 = 9, 9 + 12 = 21) or 70 feet (100 - 40 = 60, 60 ÷ 2 = 30,
30 + 40 = 70). If your ascent rate is 10 metres/30 feet per minute,
your ascent time is 2 minutes (metric: 18 ÷ 10 = 1.8 — round to
2; imperial: 60 ÷ 30 = 2).
• Ascent between stops is negligible and is handled several ways.
The easiest is to add one minute to every third stop (ignore gas
switches). Ascent from last stop to surface is generally disre-
garded.
Example: You have three deco stops of 9 metres/30 feet for 3
minutes, 6 metres/20 feet for 5 minutes and 3 metres/10 feet for
9 minutes. You would plan your gas supply assuming 10 min-
utes at 3 metres/10 feet, with the extra minute accounting for
ascent between stops.
• Remember that your bottom SAC rate usually differs from your
decompression/safety stop SAC rate; use different rates accord-
ingly.
• Estimate the required gas volume for each gas blend you’ll use.
• Typically, you round to the closest litre or cubic foot. (Some div-
ers prefer to always round up for extra conservatism, but this
isn’t required.)
• After you have a volume for each gas, multiply each gas volume
by 1.5 to get the total volume with one-third reserve (or use the
formula you learned in Chapter One for a different reserve).

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 Here are some examples. Try them on your TecRec Dive Planning
Slate (don’t worry about the columns you haven’t learned to use
yet.)

Metric
What is your total gas requirement, including one third reserve,
if your SAC rate is 20 litres per minute and you plan a dive to
30 metres for 15 minutes followed by a 3 minute safety stop at 5
metres, using air for the entire dive? Ascent rate is 18 metres per

TWO
minute.
Answer: 2103 litres

Air 1402 2103

30 15 20 4.0 1200 Air

17.5 2 20 2.8 112 Air
(ascent)
5 3 20 1.5 90 Air

Total Air = 1200 + 112 + 90 = 1402 litres

1402 x 1.5 = 2103 litres

Here’s a more detailed example involving three gas blends and

decompression:
You plan to make a dive with air by following a standard air
table. You plan to make the decompression more conservative by
using EANx50 at 9 and 6 metres, and pure oxygen at 3 metres.
Your planned dive is 45 metres for 40 minutes, with 5 minutes at 9
metres, 19 at 6 metres and 33 at 3 metres. Your SAC rate is 24 litres
per minute during the working part of the dive, and 18 litres per
minute when decompressing. Your ascent rate is 10 metres per min-
ute. What are your total gas requirements for each gas, including a
one-third reserve?
Answer: Air = 8452 l, EAN x 50 = 1077 l, Oxygen = 1194 l

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 Air 5635 8452

EANx50 718 1077

O2 796 1194

45 40 24 5.5 5280 Air

27 4 24 3.7 355 Air
(ascent)
9 5 18 1.9 171 EANx50
6 19 18 1.6 547 EANx50
3 34 (33+1) 18 1.3 796 Oxygen

Air = 5280 + 355 = 5635; 5635 x 1.5 = 8452 litres

EANx50 = 171 + 547 = 718; 718 x 1.5 = 1077 litres
Oxygen = 796 x 1.5 = 1194 litres

Imperial
What is your total gas requirement, including one third reserve, if
your SAC rate is .75 cubic feet per minute and you plan a dive to
100 feet for 15 minutes followed by a 3 minute safety stop at 15
feet, using air for the entire dive? Ascent rate is 60 feet per minute.
Answer: 78 cubic feet

Air 52 78

100 15 .75 4.0 45 Air

57.5 2 .75 2.8 4 Air
(ascent)
15 3 .75 1.5 3 Air

Total Air = 45 + 4 + 3 = 52 cubic feet

52 x 1.5 = 78 cubic feet

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 Here’s a more detailed example involving three gas blends and
decompression:

You plan to make a dive with air by following a standard air

table. You plan to make the decompression more conservative by
using EANx50 at 30 and 20 feet, and pure oxygen at 10 feet. Your
planned dive is 150 feet for 40 minutes, with 5 minutes at 30 feet,
19 at 20 feet and 33 at 10 feet. Your SAC rate is .8 cubic feet per
minute during the working part of the dive, and .65 cubic feet per

TWO
minute when decompressing. Your ascent rate is 30 feet per min-
ute. What are your total gas requirements for each gas, including a
one-third reserve?
Answer: Air = 282 cf, EANx50 = 39 cf, Oxygen = 44 cf

Air 188 282

EANx50 26 39

O2 29 44

150 40 .8 5.5 176 Air

90 4 .8 3.7 12 Air
(ascent)
30 5 .65 1.9 6 EANx50
20 19 .65 1.6 20 EANx50
10 34 (33+1) .65 1.3 29 Oxygen

Air = 176 + 12 = 188; 188 x 1.5 = 282 cubic feet

EANx50 = 6 + 20 = 26; 26 x 1.5 = 39 cubic feet
Oxygen = 29; 29 x 1.5 = 44 cubic feet

Desk Top Decompression Software

You’ve read references throughout this manual to desk top deco
software, and by now you’ve probably got a good idea of what it
is: software for the personal computer that generates custom dive

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 tables and other dive planning information. In the previous exam-
ples, you probably noticed that calculating gas requirements, while
not difficult, is a pain in the tuckus with a lots of potential for error.
Start figuring in your oxygen exposure and other variables and it
gets even more tedious.
Desk top decompression software takes care of all that for you,
greatly reducing the error potential. In tec diving, by far the trend is
away from using prepublished tables and tedious hand calculations
and toward using desk top decompression software, often combined
with dive computers. There are even dive computers that link with
desk top deco software, so you can preprogram the computer to cal-
culate the dive with specific information within a given range.

Using desk top deco software has several distinct advantages:

• It generates dive tables (for primary use or computer back up)
for your exact time/depth range and gas blends you’ll be using.
You’ll seldom find preprinted tables that get as close.
• It calculates gas supply requirements based on your SAC rates or
RMV, and adds in the reserve of your choice.
• It calculates OTU and “CNS clock” oxygen exposure.
• If you’re planning a computer dive, it provides a way to estimate
decompression, gas supply needs, oxygen exposure, etc., for dive
planning. Since you can set variables, you can make the soft-
ware calculate very similarly to your computer; preprinted tables
(especially military ones) may depart significantly from what
your computer would require for a dive.
• It reduces the potential for human error in several aspects of dive
plan.
• Most programs allow you to alter the decompression model to be
more or less conservative based on numerous factors (personal
physiology, water temp, etc.)
• With a laptop computer and portable printer, you can generate
tables in the field as needed.
• It saves time. Lots!
• It makes it feasible to quickly compare the variables of several
possible dive profiles; by hand this takes hours.
• It can automatically generate contingency tables for deeper/lon-
ger dives than the one planned.

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 Of course, using any decompression software, dive computer or dive
table carries risks that you must accept. Because people vary in
their physiology, no software, dive computer or table can guarantee
that DCS or oxygen toxicity will never occur, even within the limits
they provide. Extremely long dives, dives involving gases other than
oxygen and nitrogen, and dives with reverse profiles carry a risk of
being somewhat experimental because they may take you outside
the body of well established test data.
It’s worth noting that despite the

TWO
potential risk, desk top deco software
has an excellent track record, and
planning with it is quickly becom-
ing a standard operating procedure
for many types of tec diving. There
are several types available for you to
choose from, based on features, con-
servatism, etc. See your PADI Dive
Center or Resort about the choices
available.
Planning with desk top deco software is quickly becoming a
standard operating procedure for many types of tec diving.
There are several types available for you to choose from,
based on features, conservatism, etc.

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 Tec Exercise – 2.2

1. Using a single gas computer or table to compute your a. is a technique for getting very long no stop limits.
decompression, you (check all that apply):
b. requires switching to a higher oxygen blend after
a. interpolate the depth based on the depth mid- you ascend to a shallower level.
point.
c. is possible using special multiple gas computers.
b. determine an average depth based on five minute
interval samples. d. is possible using custom dive tables.

c. simply follow the computer or tables. 5. When breathing pure oxygen, your EAD is always
d. All of the above. ______________.

2. To use switches to higher oxygen enriched air or oxy- 6. ___________ _____________ ___________ calculates
gen to make your deco stops more conservative when the expected narcosis for a gas mix with an equiva-
using a single gas computer you (check all that apply): lent depth if breathing _________. It can be based
a. use a blend with higher oxygen than you used on on the assumptions that oxygen either is or is not
the bottom. ______________.
b. follow the computer or table’s deco requirements
as if using the same gas you used on the bottom. 7. You assume your __________ does not change when
using enriched air as compared to air because it appears
c. do not switch until you’re shallow enough to do
so without unacceptable oxygen toxicity risk. oxygen is just as ____________ as ____________.

d. None of the above. 8. The “ideal” enriched air for a dive to 43 metres/140 feet
would be __________.
3. Accelerated decompression (check all that apply)
9. Your SAC conversion factor for 39 metres/130 feet is
a. is a technique for increasing your ascent rate with
__________.
your BCD.
b. is shortening your decompression by switching to 10. Advantages and risks of using desk top deco software
a gas with more oxygen than you used on the bot- include (check all that apply):
tom. a. Calculates gas supply requirements, OTU and
“CNS clock.”
c. is possible using special multiple gas computers.
b. Allows you to estimate dive computer deco
d. is possible using custom dive tables.
requirements.
4. A gas-switch, extended no stop dive (check all that c. Saves time.
apply):
d. May have unacceptable risk if dive is outside the

body of well established test data.

Check it out:
1. c. 2. a,b,c. 3. b,c,d. 4. a,b,c,d. 5. -10 m/-33 ft. 6. Equivalent Narcotic Depth, air, narcotic. 7. END, narcotic, nitrogen. 8.
EANx26. 9. 4.9. 10. a,b,c,d.

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 Thinking Like a Technical Diver II Tec Objectives
In the last chapter you learned a bit about the
characteristics of top tec divers and looked at how Highlight or underline the
they think. By adopting their characteristics and answers to these questions
learning to think in the same ways, you’re on the as you find them:
road to becoming a successful tec diver yourself. 1. What do you assume
about every technical
One good characteristic to develop if you want to dive?
last a long time in tec diving is a moderate dose of

TWO
2. What do you take for
paranoia. Tec divers dedicate themselves to apply-
granted about a technical
ing, following and responding to the world’s most dive?
quoted aphorism, Murphy’s Law:
3. What question do you ask
Anything that can go wrong, will go wrong. yourself as you plan each
step in a technical dive?
4. What is your most impor-
Tattoo that on the back of your hand if you have tant resource in an emer-
gency, and what provides
to. Murphy’s Law serves you well as a tec diver if
this resource in an emer-
you assume that everything that can fail will fail. gency?
Assuming failures prompts you to plan for them.
5. What is the principle for
Likewise, take – about a technical dive for granted.
your gas reserves and
If you didn’t pack it, no one has it. If you don’t how do you apply it dur-
plan for someone to do it, it won’t happen. If you ing an open water deep
don’t check that the anchor’s secure, it will drag, technical dive?
etc.
As you plan each step in a dive, simply ask yourself, “What aspect
of this can fail and hurt or kill me?” For every reasonably possible
failure or problem you can imagine, have a workable solution
before beginning the dive. Within reason, make contingency plans
that do not require your teammate’s assistance as your first option.
Remember that it’s impossible to anticipate all problems — but you
can anticipate the most common and likely.

Reserve Gas
Imagine you’re at 50 metres/165 feet, right at the end of your
planned bottom time, and you get entangled enough that it’s
going to delay your ascent three or four minutes. Suppose you’ve
got only about 25 bar/350 psi left in your cylinders and that the
three or four minutes will put you over your planned decompres-
sion, for which you have only the exact amount of gas you need.
Serious trouble — you’re faced with running out of gas before you
get untangled, and if you do get undone before running out, you’re

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 going to run out of gas before completing your hang. If you don’t
drown, you get bent — not much of a choice. Now suppose the
same situation, but you’ve got lots of gas left in your doubles and a
healthy reserve in your decompression gas. Trouble? No, an irrita-
tion. You have to deco longer than you wanted, but you’ve got it
covered.
Clearly, in an emergency or faced with a problem, your most
important resource is time. Time gives you the opportunity to cor-
rect, abort or otherwise handle problems. Underwater, your gas
supply provides time, so it’s your reserve that provides the time you
need to deal with an emergency. It is especially important when
faced with an unusual emergency for which you don’t have an
immediate planned response. Treat your reserve as sacred — it has
no other purpose but for emergencies, ever. Another five minutes
on a really cool wreck is not an emergency.
The principle for your gas reserves is simple: at the end of the dive,
if you had no emergency, you should still have all your reserve.
Supposing you’re using the rule of thirds. For your bottom gas,
use no more than two thirds of supply on the bottom and during
all deco stops that you make with it — determining the pressure
at which you need to start your ascent should be part of your gas
planning (you’ll learn to do this a bit later). For decompression gas,
use no more than two thirds for all stops with each gas.
If you have no emergency and make the dive as planned, but
you finish with less than or substantially more than your planned
reserve, recheck your calculations and/or redetermine your SAC
rate. Figure out where the difference came from and account for it
in future dives.
The rule of thirds provides a margin for error in case you consume
gas more quickly than expected, to cover a regulator free flow prior
to shutting it down, and to assist a team mate with a gas supply
problem. But under some circumstances, you may want to increase
your reserve beyond a third. You might do this, for example, if
conditions are highly likely to increase your SAC rate due to exer-
tion or cold (especially your deco SAC rate), or there’s a higher than
normal possibility that you might slightly exceed your planned
depth or time. An extra reserve’s a good idea if the dive appears
reasonable to make, but your team has some unanswered questions
about particular variables. When in doubt, up the reserve.
Assume that anything that can go wrong will, take nothing for
granted and you have the basis for planning tec dives.

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 Tec Exercise – 2.3

1. Assume about every tec dive that anything that can 4. In emergency, your most important resource is
go ____________ will go ______________. ____________. You get this resource from your
2. The only thing you should take for granted about a ____________.
technical dive is ___________. 5. At the end of a dive that goes as planned, you
should have ___________ of your reserve left.
3. As you plan a tec dive, you should ask yourself,
a. most c. a third
“What aspect of this can ________ ____ ____

TWO
_______ ___ _______ _____?” b. half d. all

Check it out.
1. wrong, wrong. 2. nothing. 3. fail and hurt or kill me. 4. time, reserve. 5. d.

Team Diving II
In Chapter One, you learned that tec diving requires team diving,
which is in many respects a step up from the buddy system. You
learned that you’ve several responsibilities to your team, but that
you’re also responsible for being self sufficient, with your team
mates primarily your second option in an emergency.
Team diving means that you plan your dives as a team, and that
you dive in a compatible manner. In this chapter, you’ll begin
developing your skill in team planning, which includes several
checks and steps that you perform together as a team. It also
includes learning hand signals unique to tec diving.

A Good Diver’s Main Objective Is To Live – Team

Dive Planning
One characteristic of a tec dive is that planning and prepping for
it often takes longer than the dive itself. With what you’ve learned
already, this should come as no surprise — there’s a lot to consider
and plan for.

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 An important issue is that you don’t forget
Tec Objectives anything crucial in your dive plan. It’s easier to
keep your plan complete if you think in terms
Highlight or underline the answers of seven primary segments that comprise each
to these questions as you find
tec dive: Gas supply, Decompression, Mission
them:
objective, Oxygen, Inert gas narcosis, Thermal,
1. What are the seven primary seg- and Logistics. If you think about it, everything
ments to planning a deep techni-
you’ve learned so far fits into one of these cat-
cal dive ?
egories.
2. What recall phrase can you use
to recall the seven segments for To help you recall these, remember “A Good
planning?
Diver’s Main Objective Is To Live.” Any varia-
3. What are the substeps for each of tion that you remember better is fine, as long
the seven segments? as it hits all the points. This acronym (okay, not
4. Why do all team members on really an acronym, but close enough) stands for:
a technical dive usually use the
Good – G – Gas management
same gases?
Diver’s – D – Decompression
5. What four markings should be on Main – M – Mission
every cylinder used in a technical
Objective – O – Oxygen
dive?
Is – I – Inert gas narcosis
6. What cylinder markings should be To – T – Thermal exposure
easily read by your team mates
Live – L – Logistics
while wearing the cylinder?
7. Why must the cylinders be Within each of these segments, you have sub-
marked as described? steps and considerations that you need to plan
8. Who must check the pressure for and check before each dive. The Cambrian
and oxygen analysis of every cyl- Foundation, well known for leading edge tec div-
inder used in a technical dive? ing for science and exploration, developed using
9. What is the predive check recall these elements as the core for the dive planning
phrase for technical diving? process. Hundreds of Foundation dives show that
10. What steps do you include in a
this process works. You will usually begin this
technical dive predive check? process well before the dive, analyzing the vari-
ables that apply as you determine the optimi-
11. How, in the field, do you deter-
mine the one-third pressure for
mum gases, decompression schedule, and so on.
cylinders? You’ll review the initial plans and confirm that
it’s still appropriate (due to conditions, etc.) just
12. How do you perform a bubble
check?
prior to your dive.

13. How do you perform a descent What you’ve already learned and practiced
check? covers much of what A Good Diver’s Main
14. How do you use one hand to sig-
Objective Is To Live prompts you to remember.
nal numbers to a team mate? Here are some points you and your team need
to be sure of for each segment to assure you’re
15. What do the thumbs-up, fist and
“okay” hand signals mean during
covering the substeps; you’ll be learning more
a tec dive? about these as you progress through the course
and as you grow as a tec diver.
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 A G ood – G as management
1. Plan sufficient gas for the dive, plus the reserve, for each diver.
Determine gas actually available and compare to gas require-
ments.
2. All divers personally analyzed their gas immediately before the
dive.
3. Mark all cylinders appropriately.

TWO
4. All cylinders have a second stage at all times (except argon).
5. Test all valves and regulators.
6. Plan for gas termination, malfunction, or high gas consumption.
7. Determine turn pressure for bottom gases.
8. Confirm that team mates have compatible (ideally the same)
gases.

D iver’s – D ecompression
1. Calculate the decompression and compare it to the gas supply
planned.
2. Calculate back up decompression schedules and contingency
tables, or have a back up computer — all divers have entirely
independent methods for determining their deco.

M ain – M ission
1. The entire team understands and agrees on the mission
(objective).
2. The mission is reasonably doable within the dive plan.
3. All team members know their roles and are qualified to perform
them.
4. The mission has been made as simple as possible.
5. You can abort the dive at any point, mission notwithstanding.
6. If it would help and is possible, you have practiced the mission
on land or in shallow water first.
7. All team members agree that the primary mission is for everyone
to come back unhurt.

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 O bjective – O xygen
1. The PO2 for the planned max depth and bottom gas is 1.4 ata or less.
2. On gas-switch, extended no-stop dives, the PO2 for the second EANx
blend and depth is 1.4 ata or less.
3. The PO2 for the planned decompression stops and decompression
gases is 1.6 ata or less.
4. The oxygen exposure (OTUs and “CNS
clock”) for the entire dive stays within
accepted limits.

I s – I nert gas narcosis

1. For the planned depth and objective,
narcosis will not be a significant factor.
2. The objective has been simplified as
much as possible, and the dive planned
as shallow as possible.
3. All divers have experience working at
the planned depth and in the condi-
tions present.

T o – T hermal exposure
1. Team exposure suits are adequate for
the planned duration and any reason-
able contingency extended duration.
2. If using argon in a dry suit, there’s
adequate gas for the dive.
3. The team is prepared for the conse- A Good Diver’s Main Objective Is To Live —
something you’ll practice in repeatedly in this
quences of a major dry suit failure, if course.
dry suits are used.
4. As part of the predive check, all divers inspect and check dry suit
valves, zippers and seals for integrity and function.
5. If using a wet suit, there’s adequate buoyancy compensation and
insulation to allow for suit compression at depth.

L ive – L ogistics
This tends to be extensive and begins well before the dive. Each of the
previous segments generates logistical considerations, most involv-
ing who, how, what, where, when. Note these as you plan; examples
include:

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 1. Establish who is responsible for providing what equipment/gas etc.
2. Establish who is qualified and will handle surface and underwa-
ter support (if necessary).
3. Establish team dive leaders and project leader.
4. Establish when and where teams will meet.
5. Determine where to find the closest emergency medical facility.
6. Assure that all project members know where to find the first aid

TWO
kit and emergency oxygen, and that they know how to use it.
7. Assure that all project members know where to contact help.
8. Etceteras . . . .

Team Diving Gas Handling Considerations

As you noted in the Good step, team planning includes gas han-
dling considerations. This includes choosing the appropriate gas
blends to use, and checking and marking your cylinders so that
there’s no confusion about whose is whose, what’s in a tank or how
deep you can breathe from it safely.
Gas Selection. You and your dive team will usually plan your dive
using the same gas blends throughout the dive. In some instances,
though not as ideal, you may use different blends, but chosen so
that they’re compatible with each other’s decompression require-
ments. You do this for several reasons.
The most important reason for matched/compatible gases is so
team mates can use each other’s gases in an emergency without
compromising their deco schedules. Second, it reduces confusion
about gas switches, and what your team mates are breathing at a
given depth. Third, it allows team mates to share deco schedules in
case of lost tables, computer failure, etc. Fourth, it keeps your team
together because everyone will have similar limits and similar deco
stop requirements.
Cylinder Markings and Labels. Besides using the same gases, it’s
imperative that you mark all your cylinders — doubles, stage and
deco cylinders — appropriately. There are some regional variations
(some of which local regulations impose), but the following four
markings/labels have become generally standard among tec divers.
Color coding – Enriched air nitrox normally has a wide green band
with yellow borders, and label “nitrox” or “enriched air nitrox.”
Oxygen is normally all white or all green with large label or sten-

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 Enriched air cylinders have a Oxygen cylinders are green Argon cylinders are so small
large green and yellow band to or white and clearly labeled that they’re not likely to be
identify them. If used with air, “oxygen.” confused with other cylinders,
as these doubles are, they’re but you should still mark
still marked and handled like them clearly with a “Do Not
any other gas blend. Breathe” warning.

ciled letters reading “oxygen.” Argon is usually in a small cylinder

that has a large “ARGON — DO NOT BREATHE” label.
Analyzed content – This should be large enough
and placed so that your team mates can read it
while you’re wearing the cylinders. For example,
“EANx60” or “Oxygen.”
Maximum depth
– Near the analyzed
content and in large
figures that your team
mates can read easily,
The diver’s name and the gas blend show mark the maximum
clearly on this diver’s stage/deco cylinder. depth you can breathe
the gas blend. This is
normally based on the
1.4 ata PO2 for your doubles and stage
cylinders, and the 1.6 ata PO2 for deco/
safety stop cylinders. This is simply the
depth, such as “6 METRES” or “50 FEET.”
Since everyone’s usually using the same
measuring system, metric or imperial, it’s
more common just to have the number, You can invest in commercially
such as “6” or “50.” Characters about 5 made tank wraps with the maxi-
- 8 cm/ 2 - 3 in high are typical size. mum depths for popular blends
preprinted on them.

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 Diver’s name – This avoids confusion, especially when you stage
cylinders and retrieve them later.
As you learned during the PADI Enriched Air Diver course, cylin-
der markings are important for your safety so you don’t breathe
the wrong gas by accident. In technical diving, the cylinder mark-
ings have several safety benefits. For one, they identify whose
cylinder is whose so you dive with the cylinders you personally
checked. The markings clearly identify what is in each cylinder
and the maximum depth you can breathe from it, reducing oxy-

TWO
gen toxicity or decompression sickness risk. By marking so your
team mates can read what’s in your cylinders and the maximum
depths, you make it possible for your team mates to easily double
check what you’re breathing, and vice-versa. Finally, clear, dis-
tinct and standardized markings reduce confusion, especially
when you’re task loaded.
Additional markings – Besides the four required markings, you
may have other information on your tanks, such as the fill date
and the blender’s name and analysis. In locations where recre-
ational divers might recover “lost” cylinders they find, some divers
will also label or tag their cylinders with “Decompression Gas —
Do Not Remove.”
You can readily find commercially made labels for many of the
required markings, such as the yellow and green bands for EANx
cylinders. Others may be harder to come by, and in any event
tec divers go through a lot of labels, so it’s common to simply use
gray or white duct tape and a permanent black marker.
As a reminder, just as in recreational enriched air diving, all
divers must personally check the pressure and analyze the
contents of every cylinder they will use. No exceptions. And for
tec diving, you analyze the gas right before the dive as you set
up, even if you’ve analyzed it earlier. It’s your butt on the line —
check it yourself.

Predive Check
In the last chapter you learned that technical diving uses a pre-
dive check like recreational diving does, only expanded to meet
the demands it imposes. In fact, just as you enter the water, can
use the same recall phrase (also technically not an acronym,
but close enough) you learned as an Open Water Diver: Begin
With Review And Friend, with new and modified details for the
BWRAF. The only problem with Begin With Review And Friend

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 is that it’s not really tec-sounding, so the TecRec version is Being
Wary Reduces All Failures. (Pretty cool, huh?) This stands for:
Being - B - BCD: Confirm connection and proper operation
of all valves for both BCDs (if using a back up) or BCD and
dry suit.
Wary - W - Weight: Confirm that weight system is properly
secured. If heavy weight diving, confirm ample buoyancy
and adequate back up buoyancy.
Reduces - R - Releases: Confirm all releases and straps
are secure and intact (including mask, fins, gauges, stage
straps), that all stage/deco cylinders can be cut away, that
any large equipment can be released for ditching easily.
All - A - Air (gas): For yourself and team mates, confirm all
manifold valves are all the way open; test breath primary
and secondary, confirm that no equipment is trapping long
hose; confirm that deco cylinders are pressurized but the
valve is closed; determine the one-third-used pressure point
for your bottom gas (this is when you usually start to head
back to the ascent point; you’ll also learn to determine at
what pressure you need to be ascending — more about this
later).
1. Divide your SPG pressure by three and subtract from
total to determine when you’ve used the first third.
E.g.. If your SPG reads 210 bar, 210 ÷ 3 = 70; 210 - 70
= 140 bar. If it reads 3000 psi, 3000/3 = 1000; 3000-
1000 = 2000 psi.
2. If your pressure isn’t evenly divisible by three, round
down to the next “round” number that is, divide by
three and subtract from the total pressure. E.g.: If
pressure is 200 bar, round to 180 bar; 180 ÷ 3=60;
200 - 60 = 140 bar. If pressure is 2900 psi, round
down to 2700. 2700 ÷ 3= 900; 2900 - 900 = 2000.
Failures - F - Final Check: Check each other head to toe
looking for loose or missing gear. This step finishes in the
water with a bubble check and usually a descent check.
A bubble check looks for leaks in your manifold, first stages and
BCD. You and your team mates enter the water and dip your mani-
folds below the surface so you can check each other for bubbles.
You do the same on all your stage/deco bottles. The dive doesn’t
start until all leaks, even small ones, are handled. Sometimes you
make a bubble check by descending into shallow water, checking

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 each other, and then continuing
down on the dive. When possible,
also check regulators in the water just
under the surface.
A descent check takes place, when
feasible (it isn’t always) just after you
and your team head down at about
6 metres/20 feet or so, or at the first
level you stage your deco cylinders.

TWO
Your team pauses and you make
a final check for loose gear, correct
stage/deco cylinder placement, that
everyone’s breathing the correct gas, A descent check takes place, when feasible, just after you
and so on. You also double check for and your team head down at about 6 metres/20 feet or so,
or at the first level you stage your deco cylinders. Your team
bubbles, and sometimes, such as in
pauses and you make a final check for loose gear, correct
rough conditions, you might actu- stage/deco cylinder placement, that everyone’s breathing
ally do the bubble check during the the correct gas, and so on.
descent check instead of at the sur-
face. Due to current or logistics, sometimes you combine the descent
check with the bubble check in very shallow water (just below the
surface), or you wait until you reach the bottom.

Technical Diving Hand Signals

Most hand signals you learned for recreational diving apply to tec
diving, but there are some variations. Because BCD adjustments,
holding a line or light, etc. may occupy one hand nearly constant-
ly, tec hand signals usually use only one hand. This is especially
true for numbers, as shown on the next page.
To signal a large number, show the dig-
its rather than totals. For example, to
signal “184,” you signal “1,” then “8”
and then “4.”
Another signal that differs somewhat in
recreational diving is the “thumbs up”
signal. In recreational diving, it means
“up” or “go up” or “surface” in a rather
general sense. You determine its precise
meaning through context. In tec diving,
the signal is a command signal meaning
In tec diving, you generally respond to a signal with “end the dive now.” When a team mate
the same signal. Returning the same signal assures
that you understand your team mate’s signal. With gives thumbs up, you go — you don’t
a command signal, you always return the command dispute or question it; the dive’s over. To
signal to verify that you understand. signal something like “let’s go up there,”
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 Zero One Two

Three Four Five

Six Seven Eight

Nine

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 TWO
To signal 184, signal one, eight and four.

End the dive. Hold Okay

you point where you want to go with your index finger.

The second command signal is hold. (To signal, make a fist.) This
means stop everything while sorting through a problem or situa-
tion.
The third command signal is okay. (Same signal as in recreational
diving.) This means that you need to confirm that you are okay
because your team mate has concerns about your well being.
A final difference between signalling in recreational diving and
tec diving is that in tec diving, you generally respond to a signal
with the same signal. If your team mate signals “thumbs up,” you
reply “thumbs up, “ rather than “okay” to mean “I understand.”
Returning the same signal assures that you understand your team
mate’s signal. With a command signal, you always return the com-
mand signal to verify that you understand.

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 Tec Exercise – 2.4

1. The seven primary segments to planning a deep tech- 8. Divers must personally check the pressure and oxygen
nical dive are ___________, ____________, ______ analysis of every cylinder they will use.
______ _______, ________ _______, _______ ________, True False
_____________ and ___________. 9. The predive check recall phrase for tec diving is
2. You can remember the seven primary planning segments __________ _________ _________ ___________ _________.
by remembering A _________ ___________ _________ 10. Steps in the predive check for a tec dive include (check
________ _____ _____ __________. all that apply):
3. Substeps to each of the seven segments include (check a. checking your and your team mates BCDs and back
all that apply): up BCDs (or dry suits) connection and operation.
a. maximum depth for gases. b. confirming that all releases are secure.
b. determining contingency deco schedules. c. making sure nothing traps the long hose.
c. considering gas supply, analysis and markings. d. a bubble check and a descent check.
d. where to find the closest emergency medical facility.
11. If you have 230 bar/3400 psi, what is your one-third turn
4. Team members on a technical dive usually use the same pressure? Answer __________.
gases because (check all that apply):
12. When performing a bubble check (check all that apply):
a. it allows team mates to share gas in an emergency.
a. wait until you reach the maximum depth to per-
b. it allows team mates to share back up decompres- form the check.
sion data in case of table loss or computer failure.
b. you do not dive if there are major leaks (minor
c. it reduces confusion about gas switches. leaks are okay).
d. you generally get a better price buying large c. it’s acceptable to make the check out of the water if
volumes of the same gases. advantageous.

5. Markings that should be on every cylinder used in a d. None of the above.

technical dive include (check all that apply): 13. When making a descent check (check all that apply):
a. color coding. c. total volume. a. you usually (not always) pause at about 6
b. analyzed content. d. maximum depth. metres/20 feet.
b. confirm gear placement and double check
6. The cylinder markings that your team mates should be for bubbles.
able to read easily while you’re wearing the cylinder c. sometimes you wait until you reach the bottom.
are the ____________ ____________ and the _________
d. None of the above.
_________ for the gas blend.
14. To signal the number 27 to your team mate, you would
7. Cylinders must have the standardized markings described simply signal “9” three times, or any other combination
in this chapter (check all that apply): that totals 27. True False
a. to reduce oxygen toxicity or decompression
sickness risk. 15. In tec diving, the thumbs up signal means
b. so team mates can check each other’s breathing a. this is a way cool dive.
gases. b. let’s go up a bit.
c. to reduce confusion when task loaded. c. end the dive now.
d. to make sure that the cylinders you use are the cyl- d. Any of the above may be correct, depending on
inders you analyzed. the context.

Check it out:
1. oxygen, decompression, inert gas narcosis, gas management, thermal considerations, mission, logistics. 2. Good Diver’s Main
Objective Is To Live. 3. a,b,c,d. 4. a,b,c. d. may be true at times, but it’s not a real consideration. 5. a,b,d. 6. analyzed content,
maximum depth. 7. a,b,c,d. 8. True. 9. Being Wary Reduces All Failures (or Begin With Review And Friend). 10. a,b,c,d. 11. 160
bar/2300 psi. 12. d. 13. a,b,c. 14. False. You would give the signal for “2” and then the signal for “7.” 15. c.

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 Techniques and Procedures Tec Objectives
II – Decompression and Stage
Highlight or underline the
Cylinder Handling answers to these questions
as you find them:
In the last section, you learned that you can spend
1. What is the most impor-
more time planning a technical dive than the dive
tant skill you need for
itself takes. That’s the nature of the beast. Similarly, decompressing, and why?
when you make a deep dive that requires decompres-

TWO
2. When decompressing,
sion, you usually spend more time ascending and
what is the ideal body
decompressing than you do on the bottom. This is position and where
why so many of the skills you develop and practice should you put your stop
in the Tec Deep Diver course focus on the decompres- depth in relation to your
sion aspects of the dive — it’s actually the majority body?
of the dive. If you’re completing the Apprentice Tec 3. What is the proper ascent
Diver course, you won’t be certified for decompres- rate on a decompression
sion diving, but you’ll practice and apply some of the dive?
basics during simulated decompression dives. This 4. What is the procedure for
provides the basis for continuing later through the putting on a stage/deco
rest of the Tec Deep Diver course. cylinder?

In Chapters Three and Four, you’ll learn about deter- 5. In what order should you
stack stage/deco cylin-
mining schedules for gas-switch, extended no stop
ders?
dives and for decompression dives. For now, let’s
look at the water skills and procedures you’ll need to 6. What is the procedure for
removing and leaving a
apply those schedules; you’ll be practicing these skills
stage/deco cylinder?
beginning in Training Dive Two.
7. What is one of the most
common preventable
causes of death in techni-
Making a Decompression Stop cal diving?
In the PADI Advanced Open Water Diver course, 8. What are five guidelines
Deep Diver course and in other courses, you’ve that reduce the chance
practiced making safety stops; they’re probably rou- of accidentally switching
to an unsafe gas blend at
tine for you. Compared to a safety stop, however, a
depth?
decompression stop demands more from you. With a
safety stop, close counts — the norm is 5 metres/15 9. What is the procedure
for switching gases while
feet, but it really doesn’t matter much if you fluctu-
underwater?
ate between 6 metres/20 feet and 3 metres/10 feet.
With a decompression stop, it’s important to hold 10. What is the recall acro-
nym for gas switches, and
the required depth and not vary too much from it —
what does it stand for?
especially upward.
For this reason, the most important skill when it
comes to making decompression stops is precise buoy-
ancy control and the ability to maintain depth for extended periods.

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 Significant variation from your required stop depth can affect the
quality of your decompression, increasing your DCS risk. When
decompressing with high oxygen gases or 100 percent oxygen,
descending by accident can raise your PO2 above 1.6 ata, making
your oxygen toxicity risk — which can lead to drowning — unac-
ceptably high.
Much of the time, you can decompress on a
weighted line suspended from a boat, along a
steep-sloping bottom, on the anchor line, or with
some other fixed reference that allows you to
steady yourself at the stop depth. That’s pretty
easy. But, it doesn’t always work out that way,
and you may find yourself having to hover neu-
trally buoyant in midwater for your entire decom-
pression. It’s more tedious, but doable, and you’ll
practice doing so as part of this course.
With safety stops, it really doesn’t matter whether
you hang horizontal, vertical, upside down or
what, and it really doesn’t matter whether you
hold the stop depth at your ankles, waist, chest
or eye level. (With a safety stop what really mat-
ters is that you make one.) When decompressing,
it’s more critical. You want to keep the stop depth
at about mid chest level, and the ideal position
is horizontal. Horizontal isn’t always possible,
but the closer you can get, in theory the better
When decompressing,you want to keep the because that’s the position that maximizes the
stop depth at about mid chest level, and the lung surface area available for gas exchange
ideal position is horizontal.
when submerged.

Ascent Rate
There’s been much ado in the dive press about ascent rates, but
here’s the bottom line when it comes to decompression diving:
you ascend at the rate your dive computer or table dictates. If you
ascend too slowly or too quickly with a table, you’re deviating from
the required decompression and increasing your DCS risk; there’s
some tolerance for error, but you should try to be pretty close. If
you’re diving with a computer, ascending too slowly’s not a huge
issue because your computer will simply increase your decompres-
sion requirements as needed. However, it can’t correct much for
ascending too fast, though it will usually bleep, blink and otherwise
alert you until you slow down.

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 You’ll probably find that typical ascent for deco diving is 10
metres/30 feet per minute. Some desk top deco software and some
dive computers have variable ascent rates, with as fast as 18
metres/60 feet per minute during the deeper part of the dive, then
slowing to 10 metres/30 feet per minute, and sometimes slowing
even more near the surface. Whatever the prescribed ascent rate,
that’s the rate you should follow.

TWO
Stage/Deco Cylinder Procedures
If you’re making a decompression dive, the vast majority of the
time you’ll have one or more decompression cylinders, so let’s look
at the procedures for donning, removing and staging decompres-
sion cylinders.
Donning Stage/Deco Cylinders. A full tec rig
plus a couple of stage/deco cylinders gets pretty
heavy, so normally you kit into your doubles
and other gear, get into the water and then put
on your stage/deco cylinders (but not always —
in some places with current, divers put on stage/
deco cylinders before entering the water). Often
you’ll remove your stage/deco cylinders under-
water to lighten and streamline yourself, then
retrieve them to use later. In both cases, you
need to know how to don stage/deco bottles in
the water. To don a stage bottle, first hold it by the lower
clip and secure it to your waist D-ring. Then
Start by making sure that all the hoses are connect the top clip to a shoulder D-ring.
securely tucked under the inner tube/bungee
bands so they don’t drag or entangle you. Next,
hold the entire rig by the bottom clip in your left hand
(should be no problem with a near-neutral cylinder) and
clip it to your left hip D-ring. Then, swing the top up and
secure the upper clip to a left side chest D-ring. Check
that the cylinder’s not trapping anything you need to
access, and that the valve is closed (in case you didn’t
close it before donning it), though you may leave the
regulator pressurized.
If you’re wearing two or more cylinders, you can wear
cylinders on the right and left, or all on the left. If you’re
wearing a cylinder on the right, the most common con-
figuration is to put the higher oxygen gas on the right —
remember Right-Rich, Left-Lean. When clipping on to the

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 right hip D-ring, be cautious not to trap your long hose
under the cylinder; the hose needs to be below the clip on
the D-ring.
Wearing stacked cylinders on the left is an option often
used by scootering divers because it allows them to direct
the prop wash into unobstructed water under the right
arm. Some divers prefer wearing all cylinders on the left,
scootering or not, to avoid having to deal with keeping
the long hose free, and to keep their handling procedures
uniform. With near-neutral cylinders, left side stacking
doesn’t cause much of a balance problem.
If wearing multiple cylinders on
one side, a cylinder that you’ll stage
(leave at some point) first goes on
When clipping on to the right hip top. Likewise, the cylinder that you’re
D-ring, be cautious not to trap
your long hose under the cylinder;
breathing from goes on top; when you
the hose needs to be below the clip switch from one gas blend to another,
on the D-ring. you remove the top cylinder and either
put it underneath, or hang it from
your hip D-ring by the top clip.
Removing Stage/Deco Cylinders. Before
exiting the water, and to stage a cylinder, you’ll
need to remove your stage/deco cylinder(s). The
process is essentially donning it in reverse. First, When wearing multiple cylinders on one
confirm that the valve is closed and that you’ve side, the cylinder that you’re breathing
from goes on top.
tucked all the hoses to avoid them tangling and
snagging. Second, unclip the chest D-ring and
then grasp the clip at your hip and release it. With a full cylinder,
you may find it helpful to hold the strap with one hand while you
release the hip clip.
Particularly when removing stage/deco bottles at the
surface, you may find it easier to release the hip clip
before the chest clip. It really doesn’t matter which
way you do it, provided you can do so smoothly and
effortlessly.
Staging Cylinders. If you’re staging cylinders to
retrieve later (whether stage cylinders or decompres-
sion cylinders), the entire team stages together. Place
the cylinder some place stable, where it won’t roll
Removing a stage/deco cylinder is essen- or slide, ideally securing it to something. Reconfirm
tially the reverse of donning it. At the
that the valve’s closed so that a regulator freeflow or
surface, some divers prefer to release at
the hip first. leak can’t drain it while you’re gone. Leave it lying

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 so the second stage stays out of the mud/or sand. You and your
team mates should check each other’s bottle labels to be
sure you’re staging the correct cylinders. If you’re wearing
stacked cylinders, the one you stage first should be on top.
As you practice donning, remov-
ing and staging cylinders, initially
you’ll do this on the bottom. But you
want to learn to do so off the bottom
while swimming and while hovering.

TWO
You do this first to avoid silting out
the water, and second to save time.
You’ll practice staging on the fly,
where you remove and replace the
cylinder while swimming, pausing
only long enough to place or recover
it. You’ll also practice doing so while If you’re staging cylinders to retrieve later, the entire team
hovering, such as when you switch stages together.
cylinders while decompressing.
Whether hovering or swimming, start neutrally buoyant. When you
release a cylinder to stage it, you’ll become a bit more buoyant, so
simultaneously deflate your BCD a bit to compensate. When pick-
ing up a cylinder, you become more negative, so you simultane-
ously inflate your BCD to compensate. This takes a little practice,
but you’ll be able to stage and retrieve with no
appreciable buoyancy change.
Staging and retrieving on the fly – After
you’re comfortable donning and removing cyl-
inders stationary, learn to do so while continu-
ing to swim. Begin removing the cylinder as
you approach the stage point so you can stop,
stage and secure it quickly.
When retrieving a cylinder, pick it up and con-
tinue swimming (if it’s not your stop depth)
as you put cylinder on. When ascending to a
deco stop, if you’re close to your bottom time
and your first stop is shallower than where you
When ascending to a deco stop, if you’re staged your deco cylinder, don’t get behind
close to your bottom time and your first
your ascent time by donning at the staged
stop is shallower than where you staged
your deco cylinder, don’t get behind your depth. Simply grab the cylinder and clip it to
ascent time by donning at the staged an upper clip to chest D-ring as you continue
depth. Simply grab the cylinder and clip upward. Don completely after reaching your
it to an upper clip to chest D-ring as you
continue upward. decompression stop depth.

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 Gas Switches Underwater
Earlier you learned that switching from one gas blend to another
with more oxygen, or to 100 percent oxygen, is a primary tool for
efficient decompression and for gas-switch, extended no stop dives.
It’s one of the most important tools you have as a tec diver, and
one of the primary skills that separate technical diving and recre-
ational diving.
However, one of the most common preventable causes of technical diver
deaths is switching to the wrong gas (too high oxygen) for the depth.
When this happens, the diver often convulses from a CNS hit and
drowns. To prevent this, apply the following guidelines as much as
possible. Not all are possible on all dives, but some are possible on
all dives:
1. Most effective guideline: When feasible, never take a cylinder deeper
than you can safely breathe from it. But, for decompression you
must be certain that your return and ascent will bring you back
to your cylinders for retrieval. If getting disoriented or swept into
current are realistic possibilities, as in open ocean wreck dives,
etc., then don’t leave them behind. In controlled conditions such
as springs, lakes, quarries, tec., leaving your deco bottles at their
maximum depth to pick up later is very feasible.
2. Personally analyze your gas and mark your cylinders.
3. Block the regulator mouthpiece on cylinders that you can not
breathe from safely, so that you must remove the block before
using it. This is especially important if you must take the cylinder
deeper than the gas’ maximum depth.
4. Follow the complete gas switch procedure,
step by step, without cutting corners. The
whole point of having a procedure is so you
don’t accidentally do something fatally stu-
pid.
5. Never get complacent about staging and
gas switches — pay close attention to what
you’re doing. Don’t get distracted. Think
about what you’re doing.

NO TOX Gas Switch. Ready for another acro-

nym? (Okay, this one technically, isn’t an real-
ly an acronym either.) Here’s one that will help
The first step in a NO TOX gas switch:
keep you alive by taking your through the steps Note the gas you’re switching to and its
of a proper gas exchange: NO TOX. Typically, maximum depth by checking the labels.

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 you’re already wearing your deco cylinder before
you switch to it — if you staged it, you retrieve and
don it first. Then, the NO TOX steps go like this:
1. N – Note your name and the maximum depth on
the cylinder labels (if picking up a staged cylin-
der, you may do this as you retrieve the cylinder).
2. O – Observe the actual depth and compare it to
the maximum depth on the label.

TWO
3. T – Turn on the valve. Check the cylinder pres-
sure. When you switch off your back gas, clip
your long hose second stage to your
4. O – Orient the second stage by pulling it from right chest D-ring. This keeps it from
the retaining bands, and tracing the hose from unwinding and getting tangled.
the first stage to the second so there’s no doubt
you have the right one. Unblock the mouthpiece
(if using a block), test purge the regulator and then switch to the
new gas.
5. X – eXamine your team mates — follow the hose from their
mouths to the cylinders and confirm that they’re not deeper than
the maximum depth labeled. If necessary, signal to confirm that
you have switched (point to second stage in your mouth and
then the cylinder you’re using.)
When you switch off your back gas, clip your long hose second
stage to your right chest D-ring. This keeps it from unwinding and
getting tangled. Remember that the clip should have a breakaway
connection for hand off without unclipping in an emergency.
If you’re switching from another stage or
another deco cylinder, go to your
back gas momentarily, close the
first cylinder valve, retuck the sec-
ond stage hoses into the bands,
and then go through NO TOX as
you switch to the new cylinder. If
you’re using stacked cylinders, you
always breathe from the top cylin-
der, so you would remove the top
If you’re using stacked cylinders, like the diver on cylinder and move it underneath
the right you always breathe from the top cylin- before NO TOX switching. Or, you
der, so you would remove the top cylinder and
move it underneath before NO TOX switching.
simply clip the previous cylinder
Switch to your back gas as
Or, you simply clip the previous cylinder to your to your hip D-ring by the top clip you NO TOX switch from one
hip D-ring by the top clip and let it dangle out of and let it dangle out of the way, decompression cylinder to the
the way, which is faster. next.
which is faster.

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 If you stage your deco cylinders, not taking them deeper than you can breathe
them, you should retrieve each as you return to the stop depth where you’ll NO TOX
switch to and use each. This simplifies things if you’re stacking cylinders because the
new cylinder goes on top; you switch to back gas, don the new cylinder and then NO
TOX switch to it. If you’re wearing cylinders right and left, you’ll be breathing from
the left (lean gas) and can stay on it while donning the right (rich gas) cylinder. But,
you should switch to back gas and shut down and stow the left cylinder before NO
TOX switching to the right.

Tec Exercise – 2.5

1. The most important skill you need for decompressing is 8. Guidelines that reduce the chance of accidentally switch-
precise _________ __________ and the ability to ________ ing to the wrong gas at depth include (check all that
apply):
_________ for extended periods.
a. When feasible, don’t take a cylinder deeper than
2. When decompressing, the ideal body position is as you can safely breathe from it.
_______________ as possible, with the stop depth at b. Personally analyze your gas and mark your cylin-
about _______ ___________ level. ders.

3. The proper ascent rate on a decompression dive is c. Use mouth blocks that you must remove before
breathing from a cylinder.
a. 3 metres/10 feet per minute
d. Follow the complete gas switch procedure.
b. 10 metres/30 feet per minute
e. Pay close attention to what you’re doing. Don’t get
c. 18 metres/60 feet per minute
distracted.
d. None of the above.
9. After donning the cylinder (if necessary) and switching to
4. When donning a stage/deco cylinder, most divers find it back gas, the first step in switching gases is to
easiest to clip to the _______ D-ring first. a. turn the valve on.
5. If you stack stage/deco cylinders, the one on top is b. deploy the second stage hose.
a. the one you breathe from. c. check the actual depth.
b. the one you stage first. d. check the cylinder labels for your name and the
c. Both a and b. maximum depth
d. None of the above.
10. The recall acronym for gas switches is _____ ________. It
6. When you stage a cylinder, it’s important to leave the stands for:
valve open so that the regulator stays pressurized and ___: _______________________________________________
cannot flood.
True False ___: _______________________________________________

7. One of the most common preventable causes of techni- ___: _______________________________________________

cal diver deaths is _________ ____ _______ _________ ___: _______________________________________________
________ (____ ______ ______) for the depth.
___: _______________________________________________

Check it out:
1. buoyancy control, maintain depth. 2. horizontal, mid chest. 3. d. The proper ascent rate is the rate prescribed by your table or
computer. 4. hip. 5. c. 6. False. It’s important to close the valve so a freeflow or leak can’t drain the cylinder while you’re gone. 7.
switching to the wrong gas (too high oxygen) 8. a,b,c,d,e. 9. d. 10. NO TOX, N: Note your name and max depth on labels, O:
Observe the actual depth and compare to max depth. T: Turn on the valve. Check pressure. O: Orient second stage( pull out, trace
back to tank, unblock and test purge). X: eXamine your team mates — follow hose to cylinders to confirm proper gas.

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 Emergency Procedures II Tec Objectives
In the last chapter you learned some basic emergency
procedures, some of which you practiced during Highlight or underline the
Training Dive One. You’ll continue to practice and answers to these questions
as you find them:
refine those skills as you continue through the course.
Beginning with Training Dives Two and Three, you’ll 1. What are the emergency
procedures for having
begin practicing some of the following procedures as
your BCD fail?
well:

TWO
2. What should you do if
you experience symp-
BCD Failure toms of CNS oxygen
If you’re properly equipped, a BCD failure should toxicity?
irritate you more than scare you because it means 3. What should you do if
you’ve got to abort the dive. Properly equipped, you you see a team mate
should always be able to switch to your back up BCD breathing an unsafe (too
high oxygen) gas for the
and/or your dry suit for buoyancy control. With a
depth?
back up BCD, deploy the inflator hose (tucked in cyl-
inder bands or clipped behind BCD). 4. What should you do if
your team mate con-
If the problem is a leaking inflator filling your pri- vulses underwater?
mary BCD, disconnect the low pressure hose. Deflate 5. What should you do if
the primary entirely as you switch to the back up so you experience difficulty
you don’t have both inflated (even partially) at the maintaining your depth?
same time. 6. What is the general pro-
cedure to follow if you’re
Besides going to your back up BCD or
unable to return to your
dry suit, you may be able to use an planned ascent line?
ascent line or sloping bottom to con-
7. How do you deploy your
trol your depth while you regain con-
lift bag and reel for use
trol. If you’re overweight, you can drop as an emergency decom-
weights (if you’re wearing any) and/or pression line?
no longer needed stage/deco cylinders
8. What do you do in an
or other equipment, but this should be emergency decompres-
a last resort only because it may make sion situation if your lift
it difficult to maintain your decom- bag fails?
pression stops (it depends on your kit).
Another option is to continue to use the malfunc-
tioning BCD (but not if you’re using a back up BCD,
of course). Most BCDs will hold a good bit of gas
even with a leaking deflator or puncture, provided
Properly equipped, you should the deflator’s held low or that a puncture isn’t at
always be able to switch to your the top. With restrained wings, it may help to cut or
back up BCD and/or your dry suit
release the bungees (if possible). If the malfunction
for buoyancy control. With a back
up BCD, deploy the inflator hose. was a leaking inflator that you disconnected, use
oral inflation as you abort the dive.

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 Oxygen Toxicity
As you recall, VENTID — vision, ears, nausea, twitching, irrita-
tion, dizziness — prompts the symptoms of CNS oxygen toxicity
and may precede a convulsion. Unfortunately, there are usually
no symptoms preceding a convulsion, so you can’t count on them
to warn you — you need to stay well above 1.4 ata - 1.6 ata and
monitor your oxygen exposure.
If you do experience CNS symptoms, immediately switch to your
back gas, which should be your lowest oxygen gas. If you’re using
back gas at depth, immediately ascend. Check your depth and
reconfirm that you’re breathing the right gas — you may have
unknowingly descended below the maximum depth for the blend.
Stay on back gas for at least 15 minutes after all CNS symptoms
subside before returning to your higher oxygen gas at its maxi-
mum depth — and only do that if you must for decompression.
Otherwise, don’t switch back until shallower than the maximum
depth. If you’re using high oxygen gas for conservatism, you can
stay on your back gas to complete your deeper stops. If you’re fol-
lowing an accelerated decompression schedule, don’t count the
time on back gas as decompression. On gas-switch, extended no
stop dives, if you experience CNS symptoms, switch to back gas,
ascend immediately and abort the dive (again, the inherent risk
reduction advantage of staying within the no stop envelope).
When in doubt, ascend and get your PO2 below 1.3, or lower if
feasible. Oxygen is a less forgiving gas than nitrogen — better to
increase your risk of DCS (which is usually treatable) than to have
a substantial risk of convulsing and drowning (which is usually
fatal). If you must skip stops to ascend, extending the shallower
stops may keep your DCS risk down.

Team Mate Breathing Wrong Gas

Imagine you’re at 18 metres/60 feet and you’re completing the NO
TOX switch to EANx50. You get to X — eXamine your team mate
— and follow the hose from your mate’s mouth to . . . oh my gosh
. . . the wrong cylinder! Somehow your mate has made a major
blunder and is breathing pure oxygen!
You can lecture later about following proper procedures (which
obviously didn’t happen), but what do you do now? Signal?
Seconds count — what if your team mate doesn’t get it? Delay.
It may seem extreme, but with time critical in this situation,

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 don’t waste time trying to signal.
Immediately pull the second stage
from your team mate’s mouth and
provide your long hose. Your team
mate switches and stays on back
gas (yours or switches to own) until
establishing the correct cylinder and
sorting out the problem.
Again, NO TOX procedures avoid

TWO
this problem in the first place.

If your team mate is breathing the wrong gas, pull the

second stage from your team mate’s mouth and provide
your long hose.

Team Mate Convulses Underwater

If a team mate convulses underwater, the immediate concern is
drowning. Like any rescue situation, how you deal with it depends
on the circumstances and the resources you have at hand. These
vary so much that there’s no way to have a “standard” procedure;
you’ll have to consider your options and respond the best you can
given the situation. And as noted in the last chapter, a diver wear-
ing a full face mask has a much lower drowning risk. Although
they’re neither feasible nor common in most tec diving circum-
stances at this writing, that may change with the availability of
new designs.
If possible, hold the second stage in the diver’s mouth during the
convulsion to minimize drowning risk, but if it comes out, you’re
not likely to be able to replace it. If your team mate begins to sink,
switch to back gas before assisting so you don’t risk CNS oxygen
toxicity if you must descend in the process. Take care of yourself
first, because if you get into trouble, you can’t help and you divide
the remaining resources between yourself and the original victim.
The priority is getting the diver to the surface, but doing this may
or may not be a simple matter, especially if you have a decom-
pression obligation. If you have support divers, they can take your
team mate to the surface and initiate rescue breathing, CPR etc. as
appropriate. It’s worth noting that when taking a convulsing diver
to the surface (you or the support divers), the general recommenda-
tion is to wait for the convulsion to cease and then bring the victim
up, maintaining a neutral head position that allows air to escape
from the airway. It’s recommended that rescuers don’t drop the

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 victim’s weights before reaching the surface, because
they may lose control of victim and put themselves
at risk.
Lacking support divers, if you’re near the end of your
decompression or didn’t have a long decompression
to begin with, your DCS risk is minimal, especially if
you’ve been following a conservative profile. This is
especially true if using high oxygen to pad a single
gas table or computer; the higher the oxygen above
what the computer/table calculations assume, and
the longer you’ve been decompressing, the lower
your DCS risk.
If your risk is high, such as if you have a long hang
ahead and haven’t started it, your options become
more limited. If there’s assistance at the surface, sur-
face personnel may be able to help. Even if there’s
no one at the surface, this may still be the best you
If a team mate convulses underwater, the can do.
immediate concern is drowning. Hold the
regulator in, if possible, with the general If your DCS risk appears moderate, you may choose
recommendation to wait for the convul- to risk getting DCS, which is usually treatable, in
sion to cease before beginning the ascent.
However, getting the victim to the surface
exchange for a chance (not certainty) of saving or
is the priority. restoring your mate’s life. This is your decision — not
that it’s always an easy one.
Note that without support divers, or at least some surface support,
handling a team mate who convulses (or becomes unresponsive for
any other reason) becomes more complicated as decompression gets
longer. In this situation, you might consider planning your dives so
that your team never exceeds 1.4 ata, even during decompression.

Difficulty Maintaining Depth

Earlier you learned that buoyancy control and the ability to main-
tain depth for an extended period is one the most important skills
for decompression. Therefore, circumstances that interfere with
depth control, such as sudden BCD failure, down/up current, unex-
pected weight loss or gain from equipment dropped or taken, etc.,
have a higher consequence than when in a no stop situation.
Your first response, if possible is (obviously) to grab a line or any-
thing else to steady your depth while you regain control. This is one
reason why it’s preferable to decompress along a weighted line, on
the bottom, etc., rather than hovering. If this isn’t possible and you
begin to descend, switch to back gas to avoid oxygen toxicity (don’t
count “sink” time as decompression time). If you begin to ascend

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 and you can’t hold on to something, you may need to exhaust your
BCD and/or kick downward. If you ascend above your stop depth
momentarily (less than a minute) quickly return, add a minute
to the stop and resume your decompression (don’t count the time
above it). As a precaution, it’s also a good idea to extend your last
stop five to 10 minutes (or more).
You’ve already learned the procedures to follow if the problem lies
with your BCD. If it’s not your BCD, such as being underweight, get
team mates to give you weight, such as stage/deco cylinders they’re

TWO
through with. Support divers may be able to assist by fetching weight.
Remember that it’s critical to maintain depth while decompressing
— do not take this problem lightly.

Unable to Return to Ascent Line

In many environments, it’s reasonably likely that you won’t be able
to return to the ascent line. For instance, your team may get disori-
ented or carried down current and have to surface before regaining
the ascent line. This is so common in some environments that you
don’t even plan to return to your ascent line. Obviously, in these
conditions you either don’t stage your decompression gases, or
stage them only a short distance away where there’s virtually zero
chance of not recovering them, so there’s no question that you’ll
have them when your team ascends. Note that because a boat may
have to leave its anchor line or moor for any number of reasons, in
tec diving it’s seldom appropriate to stage deco tanks by hanging
them from lines under the boat.
To ascend away from your planned ascent line (or, you may simply
plan to follow this procedure), your team deploys a lift bag. The
team ascends along the lift bag line and completes decompression
together adrift, with the dive boat following or watching, plan-
ning to pick you up when you complete your decompression. Part
of your dive plan needs to include coordinating the procedures for
doing this with the boat crew and surface support.
Deploying a Lift Bag. When sending up a lift bag (which you’ll
practice several times throughout the course), you want to get it as
full as possible, control its ascent, maintain buoyancy control and
avoid tangling or jamming the reel, all at the same time. No wor-
ries — do this:
1. Retrieve bag and reel. Put a puff of air in it so it floats a bit for
easy handling and secure the reel line to bag clip with a double
loop.

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 2. Hold the reel out away from you in your
extended right hand, visible, with the line
tight to the bag in your left. Have the reel
unlocked, but keep it from turning with your
finger. Bring the bag to your mouth with the
opening above your second stage and inflate
it as full as you can by “puffing” your second
stage in your mouth. This technique avoids
entanglement, and it avoids freeflow by using
the second stage that’s in your mouth. You
Begin lift bag deployment by putting in a small don’t want the reel clipped to you because if it
puff of air and attaching your reel. jams, you’d go for an unwanted ride!
3. At the same, if you can, hold on to some-
thing with your legs, or have your team
mates hold you down, so you fill the
bag as much as possible without it car-
rying you upward. The more you fill it,
the better.
4. Release the bag and allow it to ascend
while maintaining some drag and ten-
sion on the reel so it doesn’t topple and
spill at the surface. Maintain tension
during your ascent and decompression,
Puff the bag as full as you can from your second
or it may spill and sink. stage (still in your mouth) with the reel unlocked
and extended away from you where you can see
5. After it reaches the surface, pull in and it. This avoids entanglement.
take up slack to make as vertical as pos-
sible. Your bubbles
tend to push it, so don’t expect it to maintain
your depth — you have to do that with buoy-
ancy control.
If Your Lift Bag Fails. If your lift bag fails
for some reason, another diver on the team
deploys the next one (every team member is
supposed to have a bag, right?). If your bag
went up but it’s not buoyant enough, you can
clip a team mate’s bag to yours with a carabi-
When decoing under a lift bag, you won’t be able
neer and send it up the same line — this adds
to hang on to the line to maintain your depth.
Instead, you use it as a reference and maintain buoyancy without the entanglement possibili-
depth with good buoyancy control. ties of another line. In some cases, the team
sends up a second bag on the line to tell sur-
face support that the entire team is there.
If your bag fails and there’s no other bag available (due to separa-
tion from your team, for example), reel your bag in and try again
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 — it may have simply spilled. If that doesn’t
work, you’ll have to decompress by hovering
and watching your depth. When you surface,
deploy your inflatable signal tube so the boat
can find you more easily. Note that some
inflatable signal tubes are designed to double
as lift bags that you can use as back up.

TWO
If your bag went up but it’s not buoyant enough, you can clip a team mate’s
bag to yours with a carbineer and send it up the same line — this adds buoy-
ancy without the entanglement possibilities of another line.

Tec Exercise – 2.6

1. If your BCD fails and you’re properly equipped, you d. switch to back gas if you’re descending.
switch to your ______ ____ _____ and/or ______ ______.
6. If unable to return to your planned ascent line, the
2. If you experience CNS oxygen toxicity, you should general procedure is
(check all that apply): a. to ascend and decompress along a line from a lift
a. switch to back (lowest oxygen) gas. bag.
b. descend until the symptoms subside. b. to split the team and conduct a broad search for
c. ascend if possible. the line.

d. confirm your depth and the gas you’re breathing. c. send up an emergency float that guides support
crew to bring the line to you.
3. If you see your team mate breathing an unsafe gas for d. None of the above.
the depth, you should
a. signal your team mate immediately. 7. When deploying your lift bag and reel (check all that
apply):
b. pull the second stage out of your team mate’s
mouth and provide your long hose. a. keep the second stage in your mouth.

c. watch a moment to give your mate a chance to b. keep the reel locked at all times.
notice. c. your team mates should stay well away from you.
d. None of the above. d. All of the above.

4. If your team mate convulses underwater, after consider- 8. If your lift bag fails after deploying it for emergency
ing your own safety the priority is getting the diver to decompression, your first option is
the _______. a. to have another team mate deploy the next one.
b. to use an inflatable signal tube as a back up.
5. If you have trouble maintaining depth, depending on
the cause you should (check all that apply): c. to decompress while hovering and watching your
a. grab a line or object. depth.

b. switch to your back up BCD and/or dry suit. d. to resume your search for the planned ascent line.

c. get additional weight from support divers or team

mates.

Check it out:
1. back up BCD, dry suit. 2. a,c,d. 3. b. 4. surface. 5. a,b,c,d. 6. a. 7. a. 8. a.

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 Performance Preview:
Objectives Practical Application Two
To successfully complete Practical Application II continues your gear rigging
this Practical Application, skills and begins developing your dive planning skills.
you will be able to:
You’ll continue to work in a team and accomplish
1. Working as a team, plan a three tasks. Chances are, your instructor will assign
theoretical dive by calcu- these for your team to complete independently, and
lating gas requirements,
then evaluate your work later (such as when meeting
maximum depths, expo-
sure suit requirements, for Training Dive Two).
methods for meeting
an objective, and other Dive Planning
particulars based on infor-
mation provided by the
Your instructor will provide SAC rates to use and a
instructor, including but dive schedule (depth, time, deco schedule) based on a
not limited to a decom- single gas table/computer. You’ll assume that you’ll
pression schedule, SAC use EANx blends to make the schedule more con-
rates, gas blends available, servative, and your instructor will tell which blends
the objective and details
might be available for your selection. You’ll also be
about the environment.
told about the dive conditions (clarity, current, tem-
2. Explain the basic features perature), etc., the dive objective and the availability
of a desktop decompres-
of surface support.
sion software.
3. Working within your Applying what you’ve learned about gas supply plan-
assigned team, rig stage/ ning and A Good Diver’s Main Objective Is To Live,
deco cylinders accord- your team will provide the instructor with a written
ing to the methodologies plan detailing:
described in Knowledge
Development Section • Gas requirements for each diver and gas, including
Two. one-third reserve.
• Description of all equipment required, including
types and numbers of cylinders for each diver, and
markings (names, max depth, etc.) on each cylin-
der.
• How you’ll accomplish the objective.
• Logistics, including emergency procedures specific
to the environment, conditions and task.

Desk Top Decompression Software

Orientation
This part is fun. You and your team will open and
play with one or more types of desk top deco software
(if available). Your instructor will show you how to
start the programs, how to get help and provide basic

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 instruction. Your goal is to get the feel of the programs, what they
do and their features. Don’t worry about creating tables, though
you certainly may if you want to. If such software isn’t available,
your instructor will refer you to web sites, provide articles, example
tables, etc. to guide you to this information from various sources.

Equipment Rigging
Working within your team, you’ll assemble two stage/deco cylin-
ders per diver as you just learned about. In configuring them, try

TWO
to think “package” — that each cylinder should be compact, have
nothing dangling and yet be easy to handle, deploy and use. Your
instructor will examine the cylinders and give you tips and sugges-
tions as needed.

Preview: Training Dive Two

Performance Objectives

To successfully complete this training dive, 6. Shut down both manifold valves and the
the you will be able to: isolator valve, switching second stages to
maintain a breathing supply, beginning
1. Working in a team, plan the dive follow-
with any valve chosen by the instructor,
ing the A Good Diver’s Main Objective Is
within 60 seconds (or within 40 seconds
To Live procedure, and perform predive
if no isolator valve).
checks following the Being Wary Reduces
All Failures procedure. 7. Deploy a lift bag from the bottom in
water too deep to stand up in.
2. Working in a team, perform a bubble
check, descent check and S-drill. 8. Swim at a steady pace at a constant
depth for sufficient time to determine
3. Independently don, remove and redon a
the SAC rate.
stage/deco cylinder on the bottom.
9. Remove and replace stage/deco cylinders
4. Independently stage a stage/deco cylin-
at the surface in water too deep to stand
der and retrieve and redon it according
in.
to the previously described procedures.
10. Demonstrate time, depth and gas supply
5. Perform gas switches to stage/deco cyl-
awareness by writing the depth and SPG
inders correctly following the NO TOX
reading at the 15 minutes bottom time
procedure.
mark.

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 Predive briefing and gearing up

Training Dive Two

• At 15 minutes bottom time, write SPG reading on your slate.
Entry
Weight check (if needed)
Bubble check
Descent
Descent check
S-drill
Don, remove and redon stage/deco cylinder
Stage and retrieve stage/deco cylinder
NO TOX gas switch
Stage cylinder
Gas shut down drill — close and reopen both regulator valves and
isolator valve, switch second stages to stay with the open valve,
within 60 seconds
Retrieve cylinders, NO TOX gas switch
Deploy lift bag — switch to back gas, then send up bag
SAC swim
Free time for fun and skill development
Ascent
Remove, replace and re-remove stage/deco cylinder at the sur-
face
Recheck weight (if necessary)
Exit
Post Dive
Performance review
Disassemble and stow equipment
Log dive for instructor signature.

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 Preview: Training Dive Three

Performance Objectives

To successfully complete this training dive, 11. Swim at least 18 metres/60 feet sharing
the you will be able to: gas with the long hose as both a donor
with a mask, and as a receiver without a
1. Working in a team, plan the dive follow-
mask.

TWO
ing the A Good Diver’s Main Objective Is
To Live procedure, and perform predive 12. Determine SAC rate by swimming at
checks following the Being Wary Reduces a slow, steady pace with a stage cylin-
All Failures procedure. der at a level depth for suffiicent time,
recording all the required information for
2. With minimal assistance, don two stage/
subsequent calculation.
deco cylinders at the surface in water too
deep to stand in. 13. Tow a simulated unresponsive, breathing
diver horizontally 6 metres/20 feet.
3. Working in a team, perform a bubble
check and descent check. 14. Perform two gas switches following the
NO TOX procedure in midwater along
4. Stage and retrieve two stage/deco cylin-
a vertical line, with the first simulating a
ders, making NO TOX gas switches.
deeper stop and the second simulating
5. Maintain a simulated decompression switching gases at a shallower stop.
stop for three minutes while breathing
15. Maintain a simulated decompression
from a stage/deco cylinder.
stop in midwater (contact with a line,
6. Stage, retrieve and replace two stage/ pool wall, or other vertical reference is
deco cylinders while continuing to swim. acceptable) for 10 minutes, noting the
required information for subsequently
7. With minimal assistance, remove and calculating the decompression SAC rate.
replace two stage/deco cylinders while
wearing no mask. 16. With minimal assistance, remove two
stage/deco cylinders at the surface in
8. Respond appropriately to a team mate water too deep to stand in.
simulating switching to the wrong gas
underwater. 17. Demonstrate depth, time and gas supply
awareness by, upon reaching the back
9. Perform the previously learned gas shut- gas SPG pressure assigned by the instruc-
down drill within 60 seconds. tor before the dive, writing the depth
10. Deploy a lift bag from the bottom in and time on a slate.
water too deep in which to stand.

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 Predive briefing and gearing up

Training Dive Three

• Upon reaching the SPG pressure designated by your instructor,
write the bottom time and your depth on your slate.
Entry
Weight check (if necessary)
Bubble check
Don two stage/deco cylinders at the surface
Descent check
S-drill (optional at instructor’s discretion)
Stage and retrieve stage/deco cylinders making NO TOX gas
switches
Hover for three minutes
Stage cylinders, retrieve and replace on the fly.
Remove and replace both stage/deco cylinders with no mask.
Team mate goes to wrong gas drill
Gas shutdown drill — within 60 seconds
Deploy lift bag
Long hose gas sharing, no mask swim
SAC rate swim
Unresponsive diver tow
Midwater (on line) NO TOX gas switches
10 min SAC rate midwater “deco stop”
Free time for practice and experience
Ascent
Remove stage/deco cylinders at the surface.
Weight recheck (if necessary).
Exit
Post Dive
Performance review
Disassemble and stow equipment
Log dive for instructor signature.
Assignments

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 Challenge
is one of the essential nutrients of human
growth. Many years ago I discovered that exploring the
undersea world and its dominions is a splendid summons of physical
and mental energies. Living safely within the ocean’s harsh physical
and chemical laws demands exquisite harmony between
mind and body.
— Dr. Joe MacInnis, Canadian Scientist
and underwater explorer,

THREE
Underwater Man, 1974

C
hapters One and Two established the
foundation and the basic framework for
becoming a tec diver; now you’ll be adding
structure. You start off with the final details
about tec diving equipment, then head into
your third discussion on gas planning. This really puts
it together because you’ll be calculating your gas sup-

THREE: The Structure

ply requirements and
Chapter oxygen exposure for
decompression dives.
You’ll need your calculator.
From there you jump into more emergencies and what
you should do when what can go wrong does. Then
you’ll look at some more techniques you’ll be practic-
ing and applying during your training dives, espe-
cially during planning and the A Good Diver’s Main
Objective Is To Live steps. The next team diving discus-
sion shows you some new signals and the team’s role
as “back ups,” followed by more on thinking like a tec
diver, which among other topics, summarizes the six
principles for surviving a tec dive. The chapter finishes
up with an overview of Practical Application Three and
Training Dives Four and Five.

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 Tec Objectives Equipment III
Slates. In recreational diving, many divers consider
Highlight or underline the slates a convenience. You’ve probably been on a
answers to these questions group dive where someone wanted a slate, and it
as you find them:
became a game to see who, among half a dozen div-
1. What are three reasons ers, actually had one.
that technical divers
consider a slate standard In tec diving it’s another story. Slates become manda-
equipment? tory equipment for three important reasons. First, you
2. What is a “jon line” and use it for communication (true in recreational div-
how do you use it? ing, too) when understanding is crucial and signals
3. What benefits does a mul- don’t do the job. Second, as you’ve noticed there’s a
tigas computer offer you? lot you need to keep track of on a tec dive, and you
don’t want to trust your well being to memory. You
4. What are the options
regarding urination for write down and take with you key information, such
long technical dives? as your decompression schedule, reserves, the pressure
when you have to start up (turn pressure), maximum
time and depth, and so on. Finally, you record your
time, depth and gas supply through-
out a dive for tracking, for comparison against
the dive plan, and for calculating SAC rate, etc.
Choose a slate that fits easily in your thigh pock-
et (or whatever pocket you have that’s easy to
get to.) You’ll be using it a lot, so be sure you can
grab it and return it easily. Although your basic
slate does the job, a good choice is a multiple-
page slate for lots of writing space. You’ll also
find specialized slates for dive planning, survey-
ing, etc. handy.
Jon Line. Under “crowded” in the dictionary Although your basic slate does the job, a
they should have a picture of six tec divers doing good choice is a multiple-page slate for
lots of writing space.
a hang at the same depth on the same anchor
line in a current. Everyone’s trying to be at the
right depth, and with a current, the tendency is for everyone to
get pushed around into the same place (hence why drift hangs are
popular when possible). It’s also tiring.
Named for Jon Hulbert, who popularized their use, a jon line is a
short line, about a metre/three feet to three metres/10 feet long that
you loop or hook around the anchor line and then clip to your har-
ness. It lets you hang floating back away from the crowd, and saves
effort since you don’t have to hang on. It opens up space for other
divers, and it reduces the chance that you’ll get blown off the line
and have to finish your deco drifting under your lift bag. They’re so

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 advantageous if you have to
hang in a current that some
divers carry two, just in case
they accidentally lose one
while deploying it.

Multigas Computers.
Chapter One introduced you
The jon line secures to the
to multigas computers and anchor or mooring line with
you’ve been reading a bit a clip, or with a loop snugged
about them in various other down on the line as shown.
discussions up to this point. A jon line is a short line, about a
They’re definitely the trend in metre/three feet to three metres/10
feet long that you loop or hook
tec diving — by the time you read this, they may even around the anchor line and then
be standard equipment. clip to your harness. It lets you hang

THREE
floating back away from the crowd,
As you learned in Chapter One, with multigas comput- and saves effort since you don’t
ers you don’t have to base your decompression sched- have to hang on.
ule on a single gas blend. Instead, you preprogram
them with three (or more) gases, and then tell them which one
you’re using throughout the dive. This has numerous benefits.
1. You can make gas-switch, extended no-stop dives with substan-
tial no decompression time. This means that when you ascend
and switch to a higher oxygen gas, you get more time due to your
multilevel profile and due to breathing less nitrogen. For example,
you’re diving with air and have a stage cylinder of EANx40. After
15 minutes at 30 metres/100 feet, you ascend to 18 metres/60 feet.
Your computer says you have 12 minutes no stop time. Better than
nothing, but hardly worth it. Switch to EANx40 and press the but-
ton telling the computer you did and presto — the number jumps to
100 minutes. Now that’s worth it — probably more time than you
have EANx40, and it’s a no stop dive.
2. Similarly, you can enjoy accelerated decompression, which
Chapter Two introduced, to reduce your hang time. As you learned,
breathing a higher oxygen gas (or even better, pure oxygen) causes
dissolved nitrogen to diffuse from your tissues much faster than if
you stayed on a lower oxygen gas. This means your decompression
is shorter. In practice, for example, you might be diving with air to
40 metres/130 feet for 30 minutes. You head up and your computer
says you have 16 minutes of deco starting at 6 metres/20 feet. You
get to 6 metres/20 feet, switch to oxygen and punch that into your
computer. Blip! The 16 minutes changes to seven minutes. That’s
the benefit of oxygen — you can do this with any higher oxygen

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 enriched air (the higher the oxygen percent, the more time you
save), but once you reach 6 metres/20 feet, pure oxygen is the opti-
mum gas for accelerating your decompression (and it has other
benefits — more about this later on).
3. You don’t need to calculate oxygen exposure manually as you
do when making gas switch dives using a single gas computer. As
you switch gas blends, the computer tracks how that affects your
oxygen exposure.
4. They simplify some contingency situations. Suppose you’re
decompressing and pow! The deco cylinder’s second stage hose rup-
tures. You shut it down and switch one of your other regulators to
it, but the rupture blew away too much gas. You run out before you
can finish the last decompression stop you were supposed to make
with that gas. Now what? Switch to your back gas (plenty of that
left) and punch that into the computer. The computer gives you the
new, longer time to finish the stop using back gas.
Multigas computers offer a lot of flexibility, but they do cost more,
and some require desk top decompression software. (That’s not a
huge disadvantage in that you’re going to want desk top deco soft-
ware anyway.)
Urination. Technical deep dives tend to be long dives — two or
more hours isn’t unusual — making a minor issue in recreational
diving into a real issue for tec divers. That’s having to urinate,
which is an especially big issue wearing a dry suit. At this writ-
ing there are three options for handling this problem, only two of
which females can apply.
The first is to wear a wet suit and to well, just go when you need to.
You’ll want to wash the suit thoroughly after the dive, needless to
say, but it won’t hurt you or the suit.
The problem with the wet suit approach is that it’s really only a
fairly warm water choice. Often the temperature’s such that a wet
suit will do the job for a brief no stop dive, but for a long tec dive
you need to go dry. Secondly, if you’re just barely staying warm
enough, relieving yourself in your wet suit may make you cold.
This is because warm fluid dilates skin capillaries and increases
blood flow to the skin, where it loses heat rapidly. It feels warm, but
the warmth you feel is your body heat going into the water.
In a dry suit, one option is adult diapers. They’re inexpensive and
you don’t have to modify your dry suit — and they’re really the
only option for females (at this writing). Unfortunately, they only

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 hold a limited capacity, after which they’re soaked and will leak.
Also, they can’t absorb a lot at once; you have to relieve yourself
slowly or it will leak into your suit. Nonetheless, many divers find
them suitable for dives up to three or four hours long. They’re also
a good option in pristine environments in which it is inappropriate
to urinate into the water.
Males can use disposable condom catheters that route waste out-
side the suit through a tube and valve. The big advantage is that
this is a limitless option — you can use it as much as needed. The
first downside is that you have to
have the valve installed, and that
you have to know how to use it.
Most require you get into a face-
down position before you open the
valve, or you risk a squeeze where

THREE
you don’t want one (no, this isn’t
a joke). They’re a bit tricky to
hook up and take apart (you need
some privacy), and they require
maintenance (follow the manu-
facturer’s guidelines). But, many
divers will tell you that one hour
Males can use disposable condom catheters that route
waste outside the suit through a tube and valve. You open
into a two hour hang, if you need
the valve to relieve yourself and then screw it shut. There it you’d happily put up with twice
are also hands-free valves available. the hassle.

Tec Exercise – 3.1

1. Reasons tec divers consider a slate standard equipment 3. Benefits of a multigas computer include (check all that
include (check all that apply): apply):
a. communication. a. making gas-switch, extended no-stop dives.
b. carrying key information. b. making accelerated decompression dives.
c. recording your depth, time and gas pressure. c. tracking your nitrogen narcosis.
d. playing games during long hangs. d. simplifying some contingency situations.

2. A “jon line” is a short cord you attach to an anchor line 4. Options for urination for long technical dives include
and your harness to make decompressing in a current (check all that apply):
easier. a. condom catheter (for males) valve systems.
True False b. disposable adult diapers.
c. use a wet suit.
d. wear highly absorbent dry suit under garments.

Check it out:
1. a,b,c. d is a common use, but it doesn’t make slates mandatory. 2. True. 3. a,b,d. c is not true because you can’t track nitrogen
narcosis; they track oxygen exposure. 4. a,b,c. d might work, but wouldn’t be a good option.

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 Tec Objectives Gas Planning III
This Gas Planning section starts bringing together the
Highlight or underline the variables that you juggle as you plan a dive: oxygen
answers to these questions exposure, decompression schedule and gas supply.
as you find them:
What you’re learning to do is to find the dive sched-
1. What is the theoretical ule that keeps you within oxygen limits, that provides
cause of gas narcosis? adequate decompression to minimize DCS risk, and
2. How does oxygen fit into what the gas requirements are. They’re all variables
the narcosis theory? that affect your dive plan — change any one, and the
3. How do you account for others change. It’s often a juggling act of finding the
narcosis in dive planning? right combination (desk top deco software really comes
4. What depth limits arise in handy doing this.)
from narcosis concerns?
5. How do you perform
an “air break” and why Narcosis – Theory and Application
should you do so? Theory. As you learned in Gas Planning II, a tec diver
6. How do you determine using air and enriched air can’t really do anything
your OTUs and OTU limits about narcosis directly because oxygen and nitrogen
for a given dive profile? are both narcotic, and your Equivalent Narcotic Depth
7. How do you calculate the (END) does not change as you change the ratio of oxy-
“CNS clock” exposure for gen and nitrogen. It’s worth looking at the theoretical
a given dive profile and basis for this.
determine its limits?
8. How do you include oxy-
The prevailing theory about gas narcosis is the Meyer-
gen concerns in determin- Overton hypothesis. It says that gas absorption into
ing the ideal enriched air nerve cell lipids interferes with nerve impulse transmis-
to use at a given depth? sion, resulting in narcosis. Gas solubility varies with
9. What is the basis of oxy- different gases depending on solubility; the higher the
gen surface interval credit, solubility, the higher the potential for narcosis.
and how do you apply it?
Oxygen is twice as soluble as nitrogen; suggesting that
10. What are six advantages it is potentially more narcotic than nitrogen. This is off-
of decompressing based
set somewhat by your body metabolizing oxygen, how-
on a single gas com-
puter or table and using ever, so it doesn’t appear to be necessary to raise your
enriched air and/or oxy- END with enriched air compared to air. Argon is more
gen for conservatism? soluble than nitrogen or oxygen, which (along with
You should also be able to: being very dense) is why it’s a poor choice as a breath-
11. Calculate the gas supply ing gas. Nitrous oxide, which you may be familiar with
requirements and oxygen from your dentist’s office, is highly soluble; essentially,
exposure for a decom- you’re narked at the surface when your dentist uses it.
pression dive based on a
single gas computer using Helium, on the other hand, dissolves very poorly into
enriched air and/or oxy- lipids. This is why more advanced forms of tec diving
gen during decompres- and commercial diving use helium in trimix (helium-
sion for conservatism.
oxygen-nitrogen) and heliox (helium-oxygen); it is

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 non narcotic. However, it has other characteristics that you have to be
aware of — including being relatively unforgiving decompression-wise
— which is why diving with helium requires special training and super
precise dive skills. Using helium, you’d be able to determine an END
that’s shallower than your actual depth.
Application. You must realize that narcosis is present on all dives — in
theory, it begins to affect you as soon as you drop below the surface,
though effects don’t become noticable for most divers until approach-
ing the 30 metres/100 foot range. Diving with some narcosis present is
acceptable (and practically speaking, unavoidable), provided it doesn’t
impair you.
Whether it causes substantial impairment is highly variable, as dis-
cussed in a moment. Proper training allows you to function properly
with some narcosis present — the use of step-by-step procedures (NO
TOX switches, for example) not only speed learning, but aid proper

THREE
functioning — what seems simple at the surface may not be as simple
under stress on a deep dive. During some of the dives in this course you’ll
practice missions and perform timed tasks that help you recognize your
response to narcosis. Diving substantially impaired can be one of
the primary hazards of deep tec diving (even when using helium
blends) — so, be conservative when dealing with narcosis. You
account for narcosis in dive planning by limiting your dives to appro-
priate depths based on:
Safety – Your primary concern is that you note and react quickly and
properly to emergencies. If you’re so narked (under the influence of
narcosis) that to react quickly and properly to an emergency is ques-
tionable, ascend immediately to a shallower depth. It may take some
time for your head to clear.
Individual susceptibility – Narcosis affects different people differently
at different times. You’re more likely to be affected adversely when
you’ve not made a deep dive recently, you’re attempting new tasks
and/or are task loaded, or you implement an emergency procedure
you’ve not practiced recently. Narcosis may affect you more readily in
more challenging conditions, such as in cold, dark lake versus a warm,
clear tropical reef. The further you are from optimal fitness, the more
likely narcosis will affect you.
Working in your favor, individual adaptation and compensation
(sometimes called, somewhat inaccurately “tolerance”) goes up and
you’ll be more able to function adequately with narcosis when you’ve
been diving regularly, working up to the depth progressively. Narcosis
becomes less of a factor when your mission and the dive requirements
are not complex, when you’ve practiced emergency procedures exten-
sively and regularly, and when you’re diving in good environmental
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 conditions. Good fitness seems to increase your ability to function
with narcosis.
Looking at these variables, you must adjust your depth limits based
on you, your team and the dive conditions. As a starting point, the
technical diving community generally observes the following nar-
cotic limits when using air or enriched air:
1. 40 metres/130 feet — limit for recreational diving, and limit for
technical penetration (cave, wreck) into overhead environments.
2. 50 metres/165 feet — general limit for technical air diving, par-
ticularly inexperienced technical divers. Note that much of the
European dive community has used this limit for decades, and it
is acknowledged by organizations such as the United Kingdom’s
Health and Safety Executive (HSE) and the South Pacific
Medicine Society (SPUMS). It also mirrors the commercial diving
limit for air of 170 feet in the USA. Using this as the air/enriched
air limit, along with proper training, equipment and making
allowances for personal and environmental factors, has a good
track record.
3. 56 metres/185 feet — 1.4 ata PO2 limit for air diving (as well as
narcosis).
Different limits apply to tec diving with helium blends.
As a technical diver, it is your responsibility to adjust your maxi-
mum depth based on how narcosis and other variables affect you
on a dive. A dive to 50 metres/165 feet on air may be simple and
acceptable in warm, tropical sea with clear water. But, the same
depth in a cold, dark lake or in strong current, etc., can be a hugely
different situation that may be
too deep. During a dive like
that, you may need to plan your
dive to a shallower maximum,
and perhaps actually dive shal-
lower than that if you or a team
mate find narcosis becoming
too strong. It’s your responsibil-
ity to adjust according to narcosis
effects because only you know how
it’s affecting you. Be conservative.
If you make a dive and discover
you could have planned to go
somewhat deeper without undue It is your responsibility to adjust your maximum depth based
risk, and there’s a reason to, you on how narcosis and other variables affect you on a dive.
Only you know how depth is affecting you.
can always go back.

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 Managing Oxygen Exposure — Continued
Chapters One and Two introduced you to the basic concepts behind
managing CNS oxygen toxicity and pulmonary toxicity. CNS tox-
icity, you’re aware, is the most immediate concern because it can
cause a convulsion that leads to drowning, and that pulmonary
toxicity is a longer term problem you have to manage. Now it’s
time to go into more about preventing both types.
Air Breaks. While decompressing on oxygen or EANx at a depth
that yields a PO2 of 1.6 ata, a switch to air (or an EANx blend with
a comparatively low oxygen fraction) gives your body a rest from
the high oxygen exposure. This is called an air break; air breaks
have been found to greatly reduce the risk of a CNS oxygen toxic-
ity convulsion. You should consider them standard practice when
decompressing, and you don’t have to limit them to a PO2 of 1.6
ata. Most divers perform air breaks at lower PO2s as well.

THREE
The typical air break is five minutes on air (or lowest oxygen gas
available) for every 20 to 25 minutes of decompression. You do not
include the 5 minutes in your decompression time when follow-
ing an accelerated decompression schedule. You may consider it
decompression time when following a single gas computer or table,
but using enriched air and/or oxygen to make the schedule more
conservative. Some desk top deco software programs can automati-
cally include air breaks in the tables they generate.

Calculating OTUs.
As you learned previously, the OTU (Oxygen Toxicity Unit or
Oxygen Tolerance Unit — depends on the reference — introduced
by Dr. Bill Hamilton as an extension of the previous UPTD [Unit
Pulmonary Toxic Dose] method) is a method for measuring your
oxygen “dose” for a given dive. This is one of your primary meth-
ods for tracking and preventing pulmonary oxygen toxicity. It’s
based on the formula:

OTUs = minutes x ((PO2 - 0.5) ÷ 0.5) 0.83

Boy, doesn’t that look like a lot of mathematical fun. Actually, it’s
not that difficult, but it’s much simpler and less error prone to use
desk top deco software, which calculate automatically, or tables
such as the Equivalent Air Depth and Oxygen Management Table.
With the table, you simply multiply OTU per minute for a given
blend at depth by the minutes at that depth. Round down to the
next deeper depth if the actual depth isn’t shown. You do this for
all depths (including your ascent and decompression/safety stops)

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 and total them to get your OTUs for the dive. Note: You accumulate
no OTUs when your PO2 is .5 ata or less.
OTU limits appear on the Oxygen Limits Table in the appendix.
Note that the total OTUs allowed per day varies depending on the
number of continuous days of diving. This is based on the body’s
ability to recover from oxygen exposure.
For example, if you’re only diving for one day, you can rack up
850 OTUs. But then you’re out of the water for a couple of days.
If you’re diving five days in a row, you can have a total of 2300
OTUs, or an average of 460 OTUs per day, as the maximum. Your
total OTUs on any of these days may exceed 460, but, you cannot
exceed 2300 for all five days combined. If the first day exposes you
to 700 OTUs, you have a total of 1600 OTUs (2300-700=1600) to
divide among the remaining four days.
The “Average OTUs per Day” column stands for the daily average
for a mission of that length. It is not a daily allowance. That is, you
cannot have 850 day one, 700 day two, 620 day three, etc. By the
way, if you ever don’t know what the OTU daily limit is (no table
available), the daily OTU limit for continuous days forever is 300
OTUs. Limit your daily OTUs to 300 and you’ll be within limits.
To calculate your OTUs and limits for a dive, total all the OTUs
for each planned depth based on the gas blend and time, includ-
ing your ascent and any safety/decompression stops, making sure
the total is within the allowable OTUs. (After the dive, you total
the OTUs for the actual dive to use in planning subsequent dives).
Normally you disregard air breaks in figuring OTUs, and when
your PO2 is less than .5 ata, you accumulate zero OTUs. You get
your OTU per minute using the Equivalent Air Depth and Oxygen
Management Tables, by finding the blend you’re using. At each
depth, you find the PO2 and OTU per minute (round to the next
deeper depth if your depth isn’t shown.)
Example (Metric):
You’re planning three days of diving, and this is the first dive of the
second day. You ended yesterday having used 705 OTUs, and you
know you’ll need 700 OTUs for the dives planned on the third day.
You plan to dive to 30 metres on air and decompress using EANx40
at 6 metres and oxygen at 3 metres as decompression “pad” follow-
ing the air-only schedule. Your planned bottom time is 40 minutes,
and the tables you plan to use require 8 minutes of decompres-
sion at 6 metres and 26 minutes at 3 metres. Your ascent rate is 10
mpm. What are your OTUs for the dive? If you make only this dive
today, do you have enough OTUs for tomorrow? If not, how many

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 more do you need? If yes, how many do you have to spare after
this dive if made as planned?
Answer: 71.2 OTUs for the dive. Yes, you would have 383.8 OTUs
left for the second day after this dive.

71.2

30 40 Air .84 .73 29.2

18

THREE
(ascent) 3 Air .59 .24 0.7
6 8 EANx40 .64 .35 2.8
3 26 oxygen 1.3 1.48 38.5

Total allowed for 3 days = 1860

1860 - 705 (day 1) - 700 (day 3) = 455 OTUs available for day 2.
455 - 71.2 = 383.8 OTUs left.

Example (Imperial):
You’re planning three days of diving, and this is the first dive of the
second day. You ended yesterday having used 705 OTUs, and you
know you’ll need 700 OTUs for the dives planned on the third day.
You plan to dive to 100 feet on air and decompress using EANx40
at 20 feet and oxygen at 10 feet as decompression “pad” following
the air-only schedule. Your planned bottom time is 40 minutes, and
the tables you plan to use require 8 minutes of decompression at 20
feet and 26 minutes at 10 feet. Your ascent rate is 30 fpm. What are
your OTUs for the dive? If you make only this dive today, do you
have enough OTUs for tomorrow? If not, how many more do you
need? If yes, how many do you have to spare after this dive if made
as planned?
Answer: 71.6 OTUs for the dive. Yes, you would have 383.4 OTUs
left for the second day after this dive.

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 71.6

100 40 Air .85 .74 29.6

60 3 Air .59 .24 0.7
(ascent)
20 8 EANx40 .64 .35 2.8
10 26 oxygen 1.3 1.48 38.5

Total allowed for 3 days = 1860

1860 - 705 (day 1) - 700 (day 3) = 455 OTUs available for day 2.
455 - 71.6 = 383.4 OTUs left.

Calculating the “CNS clock”

The “CNS clock” also manages pulmonary oxygen toxicity (primar-
ily). Although it seems somewhat redundant to calculate the “CNS
clock” and OTUs, this is the state of practice in tec diving that con-
tinues because it works well. You calculate the “CNS clock” much
the same way you calculate OTUs — by using desk top deco soft-
ware, or by using tables to determine the CNS percent per minute.
Note that some programs and tables extrapolate NOAA limits to
more increments on the “CNS clock” than others; this may produce
some differences in what different programs and tables produce.
As with OTUs, you normally disregard air breaks in calculating the
“CNS clock.” As with OTUs, you determine the CNS percents for
each depth and time, including your ascent and deco/safety stops,
and total them for your total CNS exposure for the entire dive.
You get your CNS percent per minute using the Equivalent Air
Depth and Oxygen Management Tables, by finding the blend
you’re using. At each depth, you find the PO2 and CNS percent per
minute (right next to where you found OTU per minute); as before,
round to the next deeper depth if your depth isn’t shown.

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 Example (Metric):
You dive to 33 metres using EANx32 and for 65 minutes. The EANx32
tables you’re using call for a 15 minute stop at 6 metres and 40 minute
stop at 3 metres. You plan to use 100 percent oxygen at these stops to
maximize your conservatism. Your ascent rate is 10 metres per minute.
What is your “CNS clock” at the end of the dive?
Answer: 99.8%

99.8%

THREE
33 65 EANx32 1.38 .67 43.5
20 3 EANx32 .99 .33 1.0
(ascent)
6 15 oxygen 1.6 2.22 33.3
3 40 oxygen 1.3 0.55 22.0

Example (Imperial):
You dive to 110 feet using EANx32 and for 65 minutes. The EANx32
tables you’re using call for a 15 minute stop at 20 feet and 40 minute
stop at 10 feet. You plan to use 100 percent oxygen at these stops to
maximize your conservatism. Your ascent rate is 30 feet per minute.
What is your “CNS clock” at the end of the dive?
Answer: 99.8%

99.8%

110 65 EANx32 1.39 .67 43.5

65 3 EANx32 1.0 .33 1.0
(ascent)
20 15 oxygen 1.6 2.22 33.3
10 40 oxygen 1.3 0.55 22.0

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 Oxygen Exposure and Ideal Enriched Air Blend
You learned in the last chapter to choose the “ideal” gas based
on the blend that allows the highest fraction of oxygen without
exceeding a PO2 of 1.4 at the desired depth. Pragmatically you usu-
ally work with the closest EANx blend you have available, but the
idea is to maximize your no stop time or minimize your hang time
within oxygen limits.
However, previous oxygen exposure can affect your gas choice if you
won’t have enough oxygen exposure time (OTUs and/or “CNS clock”)
remaining to make the dive. Therefore, you may need to choose a
blend with less oxygen so you have a PO2 even lower than 1.4.
For example, suppose that as part of a 15 day dive series during
which you’re keeping your OTUs within the accepted daily average
(300), you plan a repetitive dive to 21 metres/70 feet for 45 minutes.
At the start of the dive, your CNS clock is 80 percent and you have
240 OTUs for the day.
The “ideal” blend would nor-
mally be EANx45, but 45 min-
utes at 21 metres /70 feet yields
72.9(metric)/73.8 (imperial)
OTUs and 30 percent CNS, put-
ting you over both the CNS and
OTU limits. Using EANx32, how-
ever, 45 minutes at 21m/70 ft
yields 45 OTUs and 14.8% CNS,
keeping you within limits.
3_12
Remember that if your repetitive
dive is a gas-switch, extended
no stop dive or a decompres-
Remember that if your repetitive dive is a gas-switch, extended no sion dive, you need to account
stop dive or a decompression dive, you need to account for oxygen for oxygen exposure at all levels
exposure at all levels with all gases. This is particularly important
when decompressing with oxygen or EANx50 and above. with all gases. This is particular-
ly important when decompress-
ing with oxygen or EANx50 and above; the numbers go up fast,
even when you’re 6 metres/20 feet deep or less.
Using desktop deco software greatly simplifies finding an appropri-
ate gas blend for a repetitive dive with high OTUs and/or “CNS
clock.” Some divers use an alternate method of calculating the
“CNS clock,” which is to divide the actual time by the single expo-
sure time for that PO2 on the NOAA Oxygen Exposure Limits listed
on the Oxygen Limits Table.

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 Example: In calculating a dive, you will
spend 10 minutes at 30 metres/100 feet using
EANx32. What is your “CNS clock” percent for
Oxygen Toxicity:
that part of the dive? Another
Answer: 5.5% Perspective
Limit for 1.3 PO2 = 180; 10 ÷ 180 = .055 = 5.5%

I
You may use this method for each level and t might be hard to imagine
there’s a good side to the
PO2 as an alternative to the percent-per-minute
potential for oxygen toxicity,
method. Both will give you approximately the
but actually, if it weren’t for that
same answers, though you may find insignifi-
phenomenon, oxygen would have
cant variations due to rounding. significantly less decompression
benefit.

O
xygen and EANx acceler-
Oxygen Surface Interval Credit for ate your decompression
the CNS “Clock”

THREE
and extend your no stop
Between dives breathing air, your body begins limit compared to air because
you’ve replaced some (or all) of the
to reverse the chemical effects of oxygen.
nitrogen with oxygen. You’re tak-
The OTU system accounts for this in its mis-
ing in less nitrogen — but why is
sion/daily average methodology. For the CNS
it that, with respect to decompres-
“clock,” there’s surface interval halftime credit, sion, we can, for practical purposes
which is operationally similar to dive table (within limits) ignore the oxygen?
credit. CNS surface interval credit is not com-
The reason is that our bodies con-
monly used with recreational enriched air div-
sume most of the oxygen that
ing because you almost never reach oxygen
enters our bloodstream. However,
exposure limits making no stop dives with
it’s not all metabolized — there’s
EANx40 or less, so in that envelope it’s not an no way the body can metabolize
issue. (use in energy production) all the
CNS surface interval credit was initially based oxygen. Your body only needs to
generate so much energy. Your
on studies of hospital patients undergoing long
body consumes the rest of the oxy-
term oxygen exposure. Though not based on
gen by other chemical processes
divers initially, the CNS surface interval credit
going on in the body. If these pro-
system, when also used with the OTU system, cesses happen too quickly or if they
has a good field record in diver use. Different go on too long, you have oxygen
computers, desk top deco software and tables toxicity. But within limits, these
use different halftimes for this — 90 minutes is processes take most of the oxygen
the “standard halftime,” but some default to a out of the bubble-forming catego-
slightly less conservative 60 minutes (you can ry, which is why oxygen provides
usually reset it higher, though). such a huge advantage. In a sense,
without the potential for oxygen
You can apply your CNS credit several ways. toxicity, oxygen wouldn’t help tec
Enriched air computers and desk top deco divers nearly so much.
software will calculate your credit for you, but
keep in mind that not all computers/programs

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 give credit. Otherwise, you can use a table such as the CNS Surface
Interval Credit Table in the appendix.
Find your CNS percent at the start of surface interval along the side,
and where your interval falls along the side. Where they intersect is
your new CNS percent, which you add to the CNS percent you accu-
mulate during the next dive. (If your percent isn’t shown, round up
to the next greater.)

CNS SURFACE INTERVAL CREDIT TABLE

Starting 0:00 – 0:31 – 1:01 – 1:31 – 2:01 – 3:01 – 4:01 – 6:01 –
CNS% 0:30 1:00 1:30 2:00 3:00 4:00 6:00 9:00
10% 10% 8% 6% 5% 4% 3% 2% 1%
20% 20% 16% 13% 10% 8% 5% 3% 1%
30% 30% 24% 19% 15% 12% 8% 5% 2%
40% 40% 32% 25% 20% 16% 10% 6% 2%
50% 50% 40% 32% 25% 20% 13% 8% 3%
55% 55% 44% 35% 28% 22% 14%  9% 3%
60% 60% 48% 38% 30% 24% 15% 10% 4%
65% 65% 52% 41% 33% 26% 16% 10% 4%
70% 70% 56% 44% 35% 28% 18% 11% 4%
75% 75% 60% 47% 38% 30% 19% 12% 5%
80% 80% 64% 50% 40% 32% 20% 13% 5%
85% 85% 68% 54% 43% 34% 21% 14% 5%
90% 90% 72% 57% 45% 36% 23% 14% 5%
95% 95% 76% 60% 48% 38% 24% 15% 6%
100% 100% 80% 63% 50% 40% 25% 16% 6%

Example: After the first dive, your CNS was 68%. After an hour and
40 minutes, you make your second dive, which accumulates 43%
“CNS clock” time. What is your CNS percent after the dive?
Answer: 78%. After 1:40 surface interval, 68% (round to 70%) yields
35%. 35% + 43% = 78%.

As with any table, software or computer, stay well within limits and
be conservative.

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 Planning a Decompression Dive: Using a Single Gas
Computer
Now let’s start putting everything you’ve been learning together
by planning a decompression dive the simplest way possible — by
using a single gas computer, with gas switches to pad the dive and
make it more conservative. This type of deco plan has six advan-
tages that make it a good method for a lot of dive situations.
1. Maximum conservatism — this technique keeps you well within
decompression model limits.
2. Simplicity in implementing — your computer generates required
decompression and guides you through the dive.
3. Not based on maximum depth — although you’re conservative,
decompression is based on actual profile rather than the deepest
depth, which can reduce your overall deco time.

THREE
4. Gas flexibility — since the computer assumes you’re decoing
based on your back gas, you can deco on back gas or any other
blend with an equal or greater oxygen fraction (within its oxy-
gen limits); this lets you use whatever gases you have available,
and makes it easier to handle a deco gas problem (lost, regulator
malfunction, etc.) because you can always use your back gas.
5. Easy back up decompression — by using a second single gas
computer of same type, or single gas table for the gas in ques-
tion, you have a simplified back up.
6. Accelerated decompression option — once you learn accelerated
decompression techniques, you can generate accelerated decom-
pression tables with desk top deco software based on the gases
you’ll use — good for emergency get-out-of-the-water-sooner situ-
ations (such as a leaking dry suit). Keep in mind that compared
to using EANx/oxygen with an air schedule, accelerated deco is
a trade: a less conservative decompression for less time decom-
pressing.
The flexibility this technique offers makes it a good method for
gaining experience with decompression diving.
If using a single gas enriched air computer, you set it for the bot-
tom EANx, and do the same with your back up computer (if you’re
using one instead of, or in addition to, tables). If you’re using air
computers, there’s nothing to set.
You need to plan oxygen exposure and gas requirements. For this,
you’ll use a published dive table or generate one with desk top deco

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 software based on making the entire dive, including deco, using
the bottom gas. Calculate oxygen exposure based on actual gases
you’ll use, and gas requirements based on your SAC rates and the
times at depth. Don’t forget to compare your actual gas volume
with your gas requirements to be sure the gas supply you actually
have is enough to cover the dive plan.
Some readily available tables designed for commercial/military div-
ers, such as the US Navy tables, are less conservative than popular
dive computers. If using one of these, you may want to use the next
deeper depth and time for planning purposes, because that will be
closer to your dive computer’s schedule.

Example (Metric):
You plan a dive to 44 metres using a single gas enriched air com-
puter set for EANx26. You plan to decompress using EANx80 from
9 metres to the surface. You estimate that your bottom time will
be 40 minutes. Your dive tables for EANx26 show that 40 minutes
at 44 metres requires 3 minutes decompression at 12 metres, 10 at
9 metres, 17 at 6 metres and 43 at 3 metres. Your ascent rate is 10
mpm. Your SAC rate is 19 litres per minute on the working part of
the dive, and 16 lpm when decompressing.
• Following the rule of thirds, how much of each gas do you need
for this dive?
Answer: 6771 litres of EANx26; 2489 litres of EANx80
• If you have twin 18 litre cylinders with 170 bar of EANx26 do
you have enough EANx26 for the dive? If you have a 13 litre cyl-
inder with 205 bar of EANx80, do you have enough EANx80 for
the dive? How much do you have of each?
Answer: No and yes.
• What are your OTUs and “CNS clock” after the dive?
Answer: OTUs=160.8; CNS%=85.1%
• If you’ll be diving again in two and a half hours, and you’ll be
staying within the mission averages for three days of diving, how
much “CNS clock” time and how many OTUs can you have on
the second dive?

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 EANx26 4514 6771 160.8

85.1%
EANx80 1659 2489
77 min

44 40 19 5.5 4180 EANx261.43* 1.67 66.8 0.83 33.2

28 3 19 4.0 228 EANx26 1.04 1.07 3.2 0.42 1.3
(ascent)
12 3 16 2.2 106 EANx260.57 0.20 0.6 0.14 0.4
9 10 16 1.9 304 EANx80 1.54 1.81 18.1 2.22 22.2
6 17+1 16 1.6 461 EANx80 1.30 1.45 26.1 0.55 9.9
3 43 16 1.3 894 EANx80 1.04 1.07 46.0 0.42 18.1

THREE
* Note: Actual PO2 = 1.4; 1.43 from rounding on table to 45 m.

Answer: Allowable CNS = 64%; allowable OTUs = 458.5

EANx26 = 4180 + 228 + 106 = 4514 l; 4514 x 1.5 = 6771 litres
EANx80 = 304 + 461 + 894 = 1659 l; 1659 x 1.5 = 2489 liters
18 litres x 170 = 3060 litres, 3060 x 2 (doubles) = 6120 litres EANx26
13 litres x 205 = 2665 litres EANx80
OTUs = 66.8 + 3.2 + 0.6 + 18.1 + 26.1 + 46.0 = 160.8
“CNS clock” = 33.2% + 1.3% + 0.4% + 22.2% + 9.9% + 18.1% = 85.1%
After two and a half hours, CNS 85.1% = 36%; 100% - 36% = 64%
Three day mission allows 1860 OTUs, average 620 per day. 620 -160.8 = 459.2

Example (Imperial):
You plan a dive to 145 feet using a single gas enriched air computer set for
EANx26. You plan to decompress using EANx80 from 30 feet to the surface.
You estimate that your bottom time will be 40 minutes. Your dive tables for
EANx26 show that 40 minutes at 145 feet requires 3 minutes decompression
at 40 feet, 10 at 30 feet, 17 at 20 feet and 43 at 10 feet. Your ascent rate is
30 fpm. Your SAC rate is .8 cubic feet per minute on the working part of the
dive, and .65 cf when decompressing.
• Following the rule of thirds, how much of each gas do you need for this
dive?
Answer: 289.7 cubic feet of EANx26; 101 cf of EANx80

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 If you have twin 104 cf cylinders, working pressure 2400 psi, with 2500 psi
of EANx26 do you have enough EANx26 for the dive? If you have a 104
cf cylinder, working pressure 2400, with 2300 psi of EANx80, do you have
enough EANx80 for the dive? How much do you have of each?
Answer: No and no. EANx26 = 216 cf; EANx80 = 100 cf (99.8)
• What are your OTUs and “CNS clock” after the dive?
Answer: OTUs=162.8; CNS%=85.5%
• If you’ll be diving again in two and a half hours, and you’ll be staying
within the mission averages for three days of diving, how much “CNS
clock” time and how many OTUs can you have on the second dive?
Answer: Allowable CNS = 64%; allowable OTUs = 457.2

EANx26 189.9 289.7 162.8

85.5%
EANx80 67.4 101
77 min

145 40 .8 5.5 176.0 EANx261.44* 1.69 67.6 0.83 33.2

93 4 .8 4.0 12.8 EANx26 1.05 1.08 4.3 0.42 1.7
(ascent)
40 3 .65 2.2 4.3 EANx260.58 0.21 0.6 0.14 0.4
30 10 .65 1.9 12.4 EANx80 1.53 1.82 18.2 2.22 22.2
20 17+1 .65 1.6 18.7 EANx80 1.28 1.45 26.1 0.55 9.9
10 43 .65 1.3 36.3 EANx80 1.04 1.07 46.0 0.42 18.1

* Note: Actual PO2 = 1.4; 1.45 from rounding on table to 150 ft.

EANx26 =176 + 12.8 + 4.3 = 193.1 cubic feet; 193.1 x 1.5 = 289.7 cubic feet
EANx80 =12.4 + 18.7 + 36.3 = 67.4 cubic feet; 67.4 x 1.5 =101 cubic feet
2500 ÷ 2400 = 1.04, 1.04 x 104 = 108 cubic feet, 108 x 2 (doubles) =
216 cubic feet EANx26
2300 ÷ 2400 = .96, .96 x 104 = 100 cubic feet (99.8) EANx80
OTUs = 67.6 + 4.3 + 0.6 + 18.2 + 26.1 + 46.0 =162.8
“CNS clock” = 33.2% +1.7% + 0.4% + 22.2% + 9.9% +18.1% = 85.5%
After two and a half hours, CNS 85.5% = 36%; 100%-36% = 64%
Three day mission allows 1860 OTUs, average 620 per day. 620-162.8 = 457.2
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 That’s a lot of number crunching, though it’s not particularly dif-
ficult. Again, desk top deco software calculates your gas supplies
and oxygen exposure, and with most you can enter the actual
gases and the entire profile (not an accelerated deco schedule, but
with the stops entered as way points based on what you expect the
times to be using your single gas computer) to get your oxygen
exposure. But, software can’t figure out your tank capactities and
actual gas supplies. You have to do that.

THREE
Tec Exercise – 3.2

1. According to prevailing theory, the __________ the 5 metres/15 feet, your CNS percent per minute rate is
___________ of a gas, the more narcotic it is. _________ CNS percent per minute.
2. Oxygen is __________ as soluble as nitrogen. 8. When repetitive diving and diving for several days in a
row, with respect to oxygen exposure and choosing the
3. When accounting for narcosis in dive planning, you
“ideal” gas blend for a dive
must consider (check all that apply):
a. simply find the gas with its 1.4 PO 2 maximum
a. individual tolerance depth equal to or just deeper than the
b. environmental conditions planned depth.
c. task loading b. your OTUs and “CNS clock” may require a gas
with less oxygen than what would otherwise be con-
d. your team mates’ tolerance
sidered “ideal.”
4. The general limit for technical diving using air/enriched c. None of the above.
air is _________.
5. An air break is a switch to air or your lowest oxygen gas 9. Using the CNS Surface Interval Credit Table, if your CNS
for five minutes every 20 to 25 minutes while decom- percent is 73 percent, after two hours, ten minutes at
pressing. Its purpose is to reduce the risk of pulmonary the surface it is _________ percent.
oxygen toxicity.
10. The advantages of planning a decompression dive with
True False a single gas computer and EANx/oxygen as a pad to
make the schedule more conservative include (check all
6. Using the Equivalent Air Depth and Oxygen
that apply):
Management Table, when using EANx29 at 15
metres/50 feet, your OTU per minute rate is _________ a. simplicity in implementing
OTUs per minute. b. gas flexibility
7. Using the Equivalent Air Depth and Oxygen c. easy back up decompression
Management Table, when using 100 percent oxygen at d. shortest possible hang time

Check it out:
1. greater, solubility. 2. twice. 3. a,b,c,d. 4. 50 metres/165 feet. 5. False. Its purpose is to reduce the risk of CNS oxygen toxicity.
6. 0.52. 7. .83%. 8. b. 9. 30. 10. a,b,c. d is not correct — the shortest possible hang time comes from accelerated decompression.

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 Tec Objectives Emergencies III
This section on emergencies covers some situations that
Highlight or underline can happen, but by following the right procedures, you
the answers to these can handle with confidence of a favorable outcome.
questions as you find
them: Others aren’t so clear cut — but, they’re also among
the easiest to prevent if you dive conservatively and
1. What should you do if
skillfully, follow your predive preparation procedures
one of your stage/deco
cylinder regulators mal- and don’t cut any corners.
functions?
2. What should you do Stage/Deco Cylinder Regulator Failure
if your dive computer A stage/deco cylinder regulator can malfunction and
fails?
freeflow due to dirt/debris, or due to valve seat failure,
3. What should you do etc. or in cold water, due to freezing. This is one reason
if you lose your dive why you keep the valve closed until you need the cyl-
tables?
inder, especially when you stage a cylinder. You don’t
4. What should you do want to come back to an empty decompression cylinder!
if, on a decompres- The situation’s most critical with a deco cylinder on an
sion dive, you have no
decompression infor-
accelerated deco dive because you need the gas, and less
mation at all? critical when making a padded deco dive because using
back gas takes away your extra conservatism, but you
5. What should you do
if you find narcosis
can usually still decompress adequately.
affecting you or your If you have a failure and runaway free flow, close the
team mates’ abilities to
valve and switch to back gas. If you suspect that dirt/
accomplish the mission
and/or dive safely? debris in the second stage caused the freeflow, and
believe you can clear it up quickly by flushing them out,
6. What should you do
do so. Otherwise, remove the regulator and replace it
if you discover a team
mate has separated with one from another stage/deco cylinder or from off
from you? your back set. You can do this yourself, though it’s usu-
ally easier to get a team mate to help. Keep an eye on
your stop depth as you do this.
Underwater switches aren’t exactly wonderful for either regulator
because they’ll flood. But it’ll get you through the dive — after the
dive, have both regulators serviced, with special attention to the
SPGs. SPGs are dead ends that can trap water and slowly corrode
until they fail.
Note that for this to work, you need to always have at least two reg-
ulators that fit every stage/deco cylinder — the one on it and one
you can move to it. This means that if you have multiple stage/
deco cylinders, both need to be DIN or yoke system. If you have a
single stage/deco cylinder, then it needs to be DIN or yoke to match
those on your main rig. It’s acceptable, though not ideal, to carry a

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 DIN adapter so you can put a DIN regulator from your back rig on a
yoke stage/deco cylinder.
Keep in mind that switching regulators underwater may not be a
feasible option in some circumstances. In some areas, regulators for
enriched air nitrox have reverse threads from standard regulators, so
you may only have the option of using another deco cylinder regu-
lator. In cold water environments, if you regulator freeflows due to
freezing, an underwater switch may not help because water in the
new regulator may also freeze. Consider these factors when planning
your dive. If you have no other options, you may be able to use a
free flowing regulator by slightly opening and then closing the deco
cylinder valve for each breath. For a frozen regulator, it may work to
simply shut down the freeflow and wait for the regulator to warm to
the surrounding water temperature.

THREE
Dive Computer Failure
If you have not seen a dive computer failure, you have not been div-
ing enough. Well, or you’re really fortunate, because like all electron-
ic instruments, it happens. How you handle it if it happens under-
water varies, but if you’re properly prepared and equipped, it’s really
an inconvenience, not a major emergency. Your options, in order of
preference, are:
1. If still in a no stop situation, abort the dive and surface.
2. Switch to a back up computer for deco information and abort the
dive.
3. If no back up computer, decompress based on your back up depth
gauge, timer and dive tables (printed from desk top deco software).
In most instances, you abort the dive if your computer fails because
you’re on your back up system (some people dive with two comput-
ers, plus a back up depth gauge, timer and tables so they still have
back up with a single failure and may continue the dive).

Lost Dive Tables

If making a tables-based dive (such as an accelerated decompression
dive based on desk top deco software), losing your tables is as seri-
ous as computer failure — if you’re properly prepared and equipped,
it’s an annoyance. Otherwise, it’s trouble. Again, you have several
options:
1. If you’re still in a no stop situation, end the dive.
2. Switch to your back up tables. (Plus you should have your primary
schedule on your slate).

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 3. If you’ve lost your back up tables (and slate), switch to your
team mate’s back up tables (this is one reason you dive with the
same gases).
4. If those aren’t available, you and your team mate ascend
together following your team mate’s set.

No Decompression Information At All

Being without deco information on a decompression dive shouldn’t
happen. If you and your team mates dive with the same gases and
carry appropriate back up computers and/or tables/gauges, the
chances of it happening are nil. Virtually every incident where it
has happened involve a diver who didn’t have the required back
up. Think about it — to get in this situation, you have to break a
bunch of rules or be unbelievably unlucky. You have to not only
not have back up, but also be separated from your team.
But if it were to happen end the dive immediately and start up (if
you have not already), hopefully before reaching your planned bot-
tom time. Think about your planned dive — you should have some
idea of what the required stops were, such as the deepest stop, the
length of the last stop, what gases to use at which depths, etc.
Decompress as best you remember, slightly padding deeper stops.
Heavily pad the last one or two stops. Use up all your remaining
decompression gas at the last stop (5 metres/15 feet), especially
oxygen if you have it. Write down what you do so you can com-
pare it with the schedule when you get to the surface, and so you
can calculate your oxygen exposure.
After surfacing, limit activity for several hours, stay hydrated and
monitor yourself for DCS symptoms. However, provided you hadn’t
exceeded your planned depth and time, and provided you were
diving with an appropriate reserve, you should find you have over
decompressed rather than under. But dive well, and this should be
a situation you never face.

Narcosis
This is a bit repetitive to what you read earlier, but important.
Diving below 30 metres/100 feet, most people find narcosis notice-
able, but you should still be able to function normally. As you
learned earlier, experience with narcosis increases your ability to
function with it. Gain greater depth experience gradually, and take
your susceptibility, the environment, your team, etc. into account
when you plan your dives.

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 If you find that you’re having difficulty con-
centrating, accomplishing your tasks and so
on, assume that narcosis is impairing you and
ascend to a shallower depth, or if necessary,
end the dive. Do the same if one of your team
mates acts the same way.
Be especially alert for signs and symptoms
such as looking at your computer or tables
and not understanding what they’re telling
you, the inability to perform simple motor
skills (like knot tying) etc. These all alert you
that it’s time to ascend. Some divers use sig-
nals to check each other for narcosis, such as
asking each other for gas pressure. Delayed or
confused responses suggest that narcosis may

THREE
be an issue. That’s when the prudent step is to
give the thumbs up and head home.

If you find that you’re having difficulty con-

centrating, accomplishing your tasks and so
Missing Team Mate on, assume that narcosis is impairing you and
ascend to a shallower depth, or if necessary,
You’re swimming along a wreck. Two seconds end the dive. Do the same if one of your team
ago the three of you were together. Look back mates acts the same way.
and . . . where did Leo get to? Missing team
mate. Now what?
How you handle this will depend on the dive logistics, and it should
be part of the Live step in your dive plan. You can apply some
guidelines in establishing what the plan of action will be. The first
option is for the remaining team to stay together and search briefly
in the immediate area. The second option is to have a designated
point to meet, with an agreement to do a brief search, limits allow-
ing, if the team mate doesn’t show up after a specified period.
Third, if you don’t regroup after the brief search or a reasonable
wait at the designated point, return to the ascent point. You often
regroup there.
In some circumstances a separated team mate may have to ascend
separately under a lift bag. Support divers, if present, may notify
you when they’ve made contact. In any event, do not continue
the dive with a broken group — this violates the team concept. If
after enacting your plans for regrouping you can’t reunite, the dive
should end.

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 Tec Exercise – 3.3

1. If your stage/deco cylinder regulator malfunctions you 4. If, on a decompression dive, you have no decompres-
should (check all that apply): sion information at all, you should (check all that apply):
a. close the valve. a. immediately end the dive and start up.
b. switch a working regulator to the cylinder in ques- b. remember your planned schedule as best you can
tion. and decompress accordingly.
c. clean it out quickly if you believe you can and that c. pad deep stops slightly and use all your remaining
that’s the problem. deco gases at the last stop.
d. None of the above. d. kick yourself in the butt for not having the back
ups you should.
2. If your dive computer fails (check all that apply):
a. if in a no stop situation, abort the dive and sur- 5. If you find narcosis affecting you or one of your team
face. mates’ abilities to accomplish the mission and/or dive
safely, you should (check all that apply):
b. switch to a back up computer and abort the dive.
a. Ascend or abort the dive.
c. decompress based on your back up depth gauge,
b. Head for shallow water or the surface.
timer and dive tables.
c. Move up in the water column, all the way to the
d. None of the above.
top if necessary.
3. If you lose your tables on a tables-based dive, (check all d. Go deeper.
that apply):
a. if in a no stop situation, end the dive. 6. If you discover a team mate separated from the team,
your options may include (check all that apply):
b. ascend immediately without decompressing and
a. Keep the remaining team together and search
breathe oxygen at the surface.
briefly.
c. use your back up tables.
b. Meet at a designated point.
d. ascend with your team mate follow your team
c. Follow the plan for regrouping from the Live step
mate’s tables.
in dive planning
d. End the dive if you can’t reunite.

Check it out:
1. a,b,c. 2. a,b,c. 3. a,c.d. 4. a,b,c. d is appropriate, but not until after the dive. 5. a,b,c. If you checked d, burn all your certifica-
tion cards. 6. a,b,c,d.

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 Tec Objectives Techniques III
When to Make Cylinder Switches
Highlight or underline the
answers to these questions From your practice in Training Dives Two and
as you find them: Three, plus what you’ve been learning and
1. What are the guidelines applying in the Gas Planning discussions, you’ve
and procedures for when probably got a basic grasp on when you make
to switch to and from cylinder switches to go from one gas to another.
stage/deco cylinders? Let’s look at this with some more detail.
2. What are turn around The guidelines for switching differ somewhat
points, and how do you
determine them?
for stage cylinders (used for added bottom time,
you recall) and deco cylinders (used for decom-
3. How do you learn to pression). With stage cylinders, the entire team
account for environmen-
tal variables, such as cur-
switches and stages together when any one mem-
rent, visibility, tempera- ber reaches the switch pressure. On gas-switch,

THREE
ture and waves when extended no stop dives, you switch when you
planning a tec dive? ascend above the maximum depth for the gas in
4. What are four guidelines the cylinder. In this case, stage and deco cylinder
to consider when plan- switches are very similar. Note that you should
ning to tec dive in an follow the NO TOX procedure with stage cylinder
unfamiliar environment? switches as well as with deco cylinder switches.
Your tables and dive plan dictate when you
switch to your deco cylinders — usually at the
first stop depth that calls for a different gas. However, you may
switch once you ascend above the maximum depth for the gas and
use it as you ascend to the first stop.
For example, suppose your first stop calls for EANx50 at 15
metres/50 feet. You may switch to EANx50 after you ascend above
21 metres/70 feet (maximum deco depth for 50 percent oxygen) and
use it as you ascend to 15 metres/50 feet. When using desk top deco
software to plan a dive like this, you can schedule in a one minute
stop at the maximum depth to give you time to don the cylinder
and make the switch. Or, you can simply don it on the fly and NO
TOX switch as you ascend to the first stop. (Again, all gas switches
should follow the NO TOX procedure.)

Turn Around Points

Turn around points are points in the dive at which you and your
team agree to turn the dive around and head up/back to the exit.
You determine turn around points (“turn points” for short) when
planning your dives (in fact, you’ve already been learning to deter-

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 mine them). When you or a team mate reaches any one of them,
you turn the dive. Factors to consider when determining turn
around points include:
• Completing your decompression within your gas planning, with-
out using your reserve.
• The effects of total exposure time (temperature, fatigue).
• Effects on repetitive dives, if any (OTUs, CNS, deco requirements)
All dives have at least two turn around points: the turn point based
on the bottom time, and the turn point based on gas consumed.
The SPG reading at which you turn around is called turn pressure.
(Depth may be a given, so it isn’t necessarily a turn point on all
dives.)
You may have other turn points based on your mission, logistics
or unknown variables in the profile. This may include turn points
based on:
• Distance – you turn when you’ve traveled an approximate maxi-
mum distance from the exit.
• Task completion – when you accomplish your mission, the team
may agree to turn immediately to minimize decompression.
• Depth – the team agrees to turn the dive upon reaching a certain
depth.
• Depth/time combinations – the time turn around point var-
ies with the maximum depth to accommodate decompression
within the planned gas supply. For example, “the planned depth
is 36 metres/120 feet, we’ll turn at 65 minutes. If we exceed that,
we’ll use 40 metres/130 feet as the maximum depth and turn at
50 minutes.”
When setting turn points, don’t neglect the KISS (Keep It Super
Simple) principle. Too many turn around points gets complicated.
Keep it to only a few that cover the plan requirements.
Calculating Your Back Gas Turn Pressure. Calculating your back
gas turn pressure means finding the pressure at which you begin
your ascent with enough gas to complete your planned decompres-
sion and still have one third of your back gas remaining.
1. Start by determining your total back gas volume requirements
(bottom plus decompression), including reserve. Determine what
cylinders you’ll be using to have this volume and their full pres-
sure.

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 2. Now determine how much pressure (bar/psi) you ‘ll use breath-
ing that volume, and subtract that from your starting pressure.
3. For metric, divide the volume you’ll use on the bottom by the
cylinder capactity, then subtract that from the starting pressure.

Turn pressure = Start pressure - (bottom volume ÷ cylinder capacity)

Example (Metric, based on earlier example.):

Previously, you planned a dive to 44 metres using a single gas
enriched air computer set for EANx26. You plan to decompress
using EANx80 from 9 metres to the surface, with an estimated bot-
tom time of 40 minutes. Your dive tables for EANx26 showed that
40 minutes at 44 metres requires 3 minutes decompression at 12

THREE
metres, 10 at 9 metres, 17 at 6 metres and 43 at 3 metres. Your
ascent rate is 10 mpm. Your SAC rate is 19 litres per minute on the
working part of the dive, and 16 lpm when decompressing. The gas
volume results were:

Depth Time SAC C.Fac Vol Gas

44 m 40 19 5.5 4180 EANx26
28 m(a) 3 19 4.0 228 EANx26
12 m 3 16 2.2 106 EANx26
9m 10 16 1.9 304 EANx80
6m 17+1 16 1.6 435 EANx80
3m 43 16 1.3 894 EANx80

Following the rule of thirds, you determined you need 6771 litres
of EANx26. To meet this requirement, you will dive in twin 21 litre
cylinders filled to 162 bar. This gives you 6804 litres of gas (21 x 2 x
162 = 6804). By what pressure should you be starting your ascent so
that you will have a one third reserve after completing your decom-
pression?
Answer: 62.5 bar
4180 ÷ 42 (twin 21 litre cylinders) = 99.5; 162-99.5 = 62.5 bar.

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 For imperial system, the baseline method is the easiest way to find
your turn pressure. Divide the bottom volume by the baseline, and
subtract that from the starting pressure.

Turn pressure = starting pressure -(bottom volume ÷ baseline)

Example (Imperial, based on the earlier example.):

Previously, you planned a dive to 145 feet using a single gas
enriched air computer set for EANx26. You planned to decompress
using EANx80 from 30 feet to the surface. You estimated that your
bottom time will be 40 minutes. Your dive tables for EANx26 show
that 40 minutes at 145 feet requires 3 minutes decompression at 40
feet, 10 at 30 feet, 17 at 20 feet and 43 at 10 feet. Your ascent rate
is 30 fpm. Your SAC rate is .8 cubic feet per minute on the working
part of the dive, and .65 cf when decompressing. The gas volume
results were:

Depth Time SAC C.Fac Vol Gas

145 ft 40 .8 5.5 176.0 EANx26
93 ft(a) 3 .8 4.0 9.6 EANx26
40 ft 3 .65 2.2 4.3 EANx26
30 ft 10 .65 1.9 12.4 EANx80
20 ft 17+1 .65 1.6 17.7 EANx80
10 ft 43 .65 1.3 36.3 EANx80

Following the rule of thirds, you determined you need 285 cf of

EANx26. To meet this requirement, you will dive with twin 140
cubic foot 2400 working pressure plus-rated (10% overfill) cylinders
filled to 2640 psi. This gives you 308 cubic feet of gas (140 x 2 =
280, 280 + 28 (10% overfill) = 308). By what pressure should you be
starting your ascent so you will have a one third reserve after com-
pleting your decompression?
Answer: 1136 psi
Baseline = .117 (280 ÷ 2400 = .117)
176 ÷ .117 = 1504; 2640 - 1504 = 1136

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 Most desktop deco software does
not calculate turn pressure because
it doesn’t know what size cylinders
you’re using. Therefore, you need
to calculate it yourself (but desktop
deco software, of course, will cal-
culate the volume requirements,
making it a simple process). Notice
that when you determine your turn
pressure this way, any gas you
have in your back cylinders beyond All dives have at least two turn around points: the turn point
the planned required volume gets based on the bottom time, and the turn point based on gas
consumed.
added to your reserve.
Half Plus 15 bar/200 psi Rule.

THREE
As a “shortcut” many divers use the “half + 15 bar/200 psi” rule
— take half your doubles pressure and add 15 bar/200 psi. You
should be ascending by then. This generally works well (actually
conservatively, if you compare to previous examples) when most
of your decompression will be made with deco cylinders. If you
will use back gas for more than the first one or two stops, calcu-
late as shown to be sure you’ll be started up with ample gas for
decompression plus reserve.

Environmental Variables
Tec diving is like recreational diving in that the procedures and
techniques vary with the environment. Many of the techniques
and procedures you learn in this course will be area specific, just
as they were where and when you became an Open Water Diver.
When tec diving in a new area, as in recreational diving, you
want an orientation to the new area and to any special proce-
dures and techniques that apply to it. Get this orientation from an
experienced local tec diver, ideally, a technical diving instructor.
There are four guidelines you can follow to help minimize difficul-
ties you might run into when tech diving in a new environment.
1. Gain experience with a new environment before making chal-
lenging tec dives in it. Make recreational and/or no stop dives
initially.
2. Master new, area specific equipment and procedures in con-
trolled conditions before applying them on more challenging
tec dives.

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 3. Consult local tec divers. Local methodologies evolve based on
local needs; just because something works well in one environ-
ment doesn’t mean that it’s suited to another.
4. Recognize the difference between local methods and inappropriate
methods. In the DSAT Tec Deep Diver course, you learn princi-
ples that apply universally to managing your risk in the tec envi-
ronment. The application methods may vary, but the principles
remain.
Disregarding tec diving principles is not a “local method.” That is,
suppose divers in an area commonly dive to 60 metres/200 feet
using standard recreational single cylinders and regulators. This
does not constitute a local tec diving method because it ignores
having an independent regulator in a technical environment — a
basic survival principle in the technical envelope. It’s not even tec
diving. It’s Russian roulette.

Tec Exercise – 3.4

1. Guidelines and procedures for when to switch to and 3. The best way to learn to account for environmental
from stage/deco cylinders include (check all that apply): variables, such as current, visibility, etc., in planning
a. With stage cylinders, the entire team switches and tec dives is to get an ________________ from a local tec
stages together.
diver or tec instructor.
b. Your tables and dive plan dictate switches to deco
cylinders. 4. Guidelines to consider when planning to tec dive in an
unfamiliar area include (check all that apply):
c. All deco cylinder switches are NO TOX switches. a. Gain experience making recreational and/or no
d. Stage cylinder switches are usually not NO TOX stop dives initially.
switches. b. Master new, area specific equipment and proce-
dures in controlled conditions.
2. A turn point is a time, SPG pressure or other point at
which you and the team have the option of ending c. Consult local tec divers.
the dive. d. Recognize the difference between local methods
True False. and inappropriate methods.

Check it out:
1 a,b,c. d is incorrect because all gas or cylinder switches should be NO TOX switches. 2. False. At a turn point you end the dive;
no option. 3. orientation. 4. a,b,c,d.

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 Tec Objectives Team Diving III
More Hand Signals
By the end of this section,
you should be able to: Here are some more signals unique to tec div-
ing. You’ve probably already learned some or
1. Demonstrate and recognize
the hand signals for:
all of these from your instructor during your
• line training dives, but let’s go over them anyway
• entanglement so the underwater photographer doesn’t feel
• reel like he took all these pictures for nothing.
• I think I’m bent.
• question Use the line signal for anything pertaining to a
• Turn the dive. line. You might use this to ask where a line is,
2. Identify where your team or to signal a team mate that you’ve spotted a
mates rank in your chain of line.
back up systems.
The entanglement signal is the same signal as
You should also highlight

THREE
line, but waved in an eight-shape. Try to avoid
or underline the answers to needing this one too much.
these questions as you find
them: The reel signal is for anything about a reel or
3. What is the one back up reels, and the I think I’m bent signal obviously
your team mates provide means you suspect you have DCS. Knowing
that you cannot provide how to signal that you may be bent is impor-
yourself? tant because it allows your support divers and/
4. What are the duties of a or team mates to prepare to handle the emer-
safety/support diver? gency at the surface even before you get there.
To be clear that you’re asking something, start
with the question signal. You might signal,
question - reel, to ask “Do you have the reel?”
Since thumbs up is a command signal that means end the dive
immediately, tec divers have a second signal, turn the dive. The turn
the dive signal means, “Okay, it’s time to go, but no emergency or

Line. Entangled. Reel.

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 I think I’m bent. Question Turn the dive.

hurry.” You might use this signal when you hit a turn point. Or,
before you hit one, if you’re feeling a bit cold and your team mates
look a bit bluish, you might signal, question - turn the dive, to ask
“Hey, no emergency, but maybe we should we turn the dive?”

Your Team Mates as Back Up Systems

In recreational diving, your team mate is your primary back up
system — your first option in the back up chain for most emergen-
cies. This is entirely appropriate within the recreational envelope
because in an emergency, all you have to do is get to the surface.
In tec diving, your team mate is not your primary back up system.
In tec diving, you rely on yourself first and you should have back
ups for practically everything. Therefore, your team mate is second,
third or even further into your back up chain, providing a back up
only if your self reliant back ups fail.
The single exception is that your team
mates provide your “back up brain,”
which is the only back up you can’t pro-
vide yourself. This means you and your
team mates dive paying attention to lim-
its, the plan and what’s going on. You
dive as though you might have to finish
the dive alone; no one follows everyone
else blindly.
Team mates signal each other if they
Team mates signal each other if they notice anything out
of sorts. They remind each other to check gas supplies,
notice anything out of sorts. They
time, depth, and so on. Team mates never assume that remind each other to check gas supplies,
another is either right or wrong. If they disagree about time, depth, and so on. Team mates
what’s happening or what to do, they resolve the confu-
never assume that another is either right
sion or end the dive if they can’t.

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 or wrong. If they disagree about what’s happening or what to do,
they resolve the confusion or end the dive if they can’t.
That ‘s teamwork.

Duties of the Safety/Support Diver

Part of team diving often involves handling support tasks and safe-
ty. This is especially true when you’re less experienced and working
on a large project. Although taking your turn assisting with safety
and support may not seem glamorous, it’s a great way to gain
experience and learn amid substantially more experienced divers.
A safety/support diver generally stays within the no stop limits and
attends to divers decompressing. Duties may include, but are not
limited to:

THREE
1. Checking on divers, assuring they have ample gas, etc.
2. Shuttling gear — exhausted stage/deco cylinders, unneeded
equipment up; extra gas, weights down, etc.
3. Watching for and locating divers separated from their teams.
Notifying teams that missing divers are located.
4. “Baby-sitting” — hovering near decoing divers to be ready to
assist.
5. Sitting standby on the boat or shore, fully geared up and ready
to go in to assist in an emergency.
6. Coordinating the boat crew with the needs of the decoing divers.
7. Shuttling communications between the divers and surface sup-
port.

Tec Exercise – 3.5

1. This signal means ___________. [3-28, “Reel” signal 4. The duties of a safety/support diver include (check all
inserted here.] that apply):
a. Check on divers.
2. In your chain of back up systems, your team mates rank
______ or _______, or even further in. b. Shuttling gear.
c. “Baby-sitting.”
3. The one back up your team mates provide that you can-
not provide yourself is a back up __________. d. Standby on the boat or shore.

Check it out:
1. reel. 2. second, third. 3. brain. 4. a,b,c,d.

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 Tec Objectives Thinking Like a Tec Diver III
Self Sufficiency
Highlight or underline the
answers to these questions By now “self sufficiency” should be well hammered
as you find them: into you. Your team mate only backs you up after all
1. What assumption do your back ups fail. Tec divers plan their dives assum-
technical divers make ing that they may have to complete a dive alone,
when they plan a dive? separated from the rest of the team. When you make
2. What is a “trust me” dive this assumption, you necessarily plan a self sufficient
and why do technical dive.
divers avoid them?
Self sufficiency helps you manage risk because you’re
3. What do technical div- better prepared to handle problems unaided if neces-
ers do with superfluous sary. You’ve had to think about problems ahead of
equipment in an emer-
gency?
time, and you, and your team, have multiple resourc-
es to apply to manage a single problem.
4. How do you “think back-
wards” to assist with But, though you’re self sufficient, you and your team
planning for possible work together, maintaining your “back up brains”
emergencies? for each other. And, while you should be able to
5. What are six principles handle problems by yourself, when the time comes,
for surviving a tec dive? you and your team mates help each other as much
as possible.

“Trust Me” Dives

A “trust me” dive is a dive in which one diver relies on another to
complete the dive safely. Tec divers avoid them because on a “trust
me” dive, you dive using your “back up brain” only — your brain
isn’t up to the dive. On a “trust me” dive, separation from the
leading diver may make it impossible to complete the dive safely.
Following a more experienced diver is not a “trust me” dive if you
can, at any point in the dive, abort and complete it without assis-
tance. In this case, you’re gaining experience and extending your
limits by learning from a more seasoned diver — quite another
situation.
You should ask yourself whether you would be capable of finish-
ing a planned dive entirely on your own from any point in a dive,
or in an emergency, be reasonably able to assist a team mate from
any point in the dive. If you can’t say “yes,” then you’re not ready
for the dive.
“Trust me” dives usually result when divers attempt dives well
beyond their experience and training. If you ever find yourself

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 considering one, stop and remember that you’re
probably going beyond what you’re ready to
take on. Remember, any diver can abort the dive
at any time. That includes aborting a “trust me”
dive before it begins.

Equipment is Disposable
As a tec diver, you’ll invest a lot in your gear
and in maintaining it. Some individual items,
such as multigas computers, cost a lot. But, you
have to have the mindset that it’s all dispos-
able in an emergency. In the extreme, anything
that’s superfluous to handling an emergency
and completing a dive safely is disposable and

THREE
gets ditched immediately. An empty stage bottle In the extreme, anything that’s superfluous
to handling an emergency and completing
that’s hindering an ascent to safety is a liability. a dive safely is disposable and gets ditched
Throw it away. immediately. An empty stage bottle that’s
hindering an ascent to safety is a liability.
Similarly, you can’t get attached to your gear. Throw it away.
If something can’t do the job right, you replace
it, no matter how new, how expensive or how
many years of great service it’s given you.

Thinking Backwards
Dive planning and emergency preparation is a mental process
based on anticipating the mission needs and preparing for realistic
problem scenarios. A good strategy for emergency planning is to
include thinking backwards in your dive planning.
Imagine you’re at the furthest point in your dive. Imagine realistic
problems that might stand between you and returning safely to the
surface. For each one, think about what you need to survive the
dive independently, then make sure you have those resources.
It’s a simple, yet effective process, but a few cautions. First, don’t
create a problem by carrying gear or following a procedure in try-
ing to solve an unrealistic problem. Let your imagination run away
with you and eventually you’ll stop diving as you think up scenar-
ios you can’t solve. You can fantasize equally unsolvable horrors
about walking down the street, but (hopefully) you don’t really let
these thoughts keep you from sauntering down to the corner
market.

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 Second, work one problem at a time as you go through the dive
mentally, and beware of “paralysis through analysis.” Think things
through and then move on. Over analyzing is no more useful than
under analyzing.

Principles for Surviving a Tec Dive

You may have noticed that this course focuses on being alive and
unhurt after a tec dive. (A Good Diver’s Main Objective Is To Live).
Therefore, the six principles for surviving a tec dive should be noth-
ing new to you. Think of these as survival principles you never vio-
late, though there may be different ways to follow them, depending
upon the environment.
The Principle of Secondary Life Support. You should have at least
two independent usable regulators, at least two independent sources
of time, depth and decompression information, and at least two
methods for controlling buoyancy. You should have at least two of
anything that keeps you alive. If any one fails, you abort the dive
on the other.
The Principle of Gas Reserve. You should have ample gas to han-
dle reasonably possible emergencies and still complete your decom-
pression (usually thirds). During an emergency, time is what you
need to solve the problem — your reserve gives you that time.
The Principle of Self Sufficiency. At any point in a dive, you
should be able to complete it independently.
The Principle of Depth. Your dive plan should account for nar-
cosis, decompression, oxygen toxicity and gas supply needs based
on a planned depth and/or a maximum contingency depth (and
times) that you do not exceed.
The Principle of Simplicity (KISS principle). Your dive should be
planned as simple as possible, with complexities eliminated.
The Principle of Procedure and Discipline. You follow the rules
and work the procedures without exception on every dive, no mat-
ter how familiar the dive and no matter how much experience you
have. To state this in a negative context: Cutting corners kills.

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 Tec Exercise – 3.6

1. Tec divers plan their dives assuming they’ll have to fin- 6. The six principles for surviving a tec dive are:
ish the dive ____________.
1. The Principle of _________________________________
2. A “trust me” dive is a dive in which one diver ______on _______________
another to complete the dive safely.
2. The Principle of _________________________________
3. Anything that’s superfluous to handling an emergency _______________
and completing a dive safely is ___________.
3. The Principle of _________________________________
4. To apply “thinking backwards” to assist with planning _______________
for possible emergencies, you (check all that apply):
a. Imagine realistic problems — that might stand 4. The Principle of _________________________________
between you and returning safely to the surface. _______________
b. For each, think about what you need to survive
5. The Principle of _________________________________
the dive.
_______________
c. Be sure you or a team mate has what it takes to

THREE
solve each problem. 6. The Principle of _________________________________
d. Avoid trying to solve unrealistic problems. _______________

Check it out:
1. alone. 2. relies. 3. disposable. 4. a,b,d. c is incorrect because you should be able to solve problems independently. 5. Secondary
Life Support, Gas Reserve, Self Sufficiency, Depth, Simplicity, Procedure and Discipline.

Preview:
Performance Objectives
Practical Application Three
During this practical application, you’ll
To successfully complete this Practical
Application, you will be able to: work in teams to plan Training Dives Four
and Five based on information your instruc-
1. Working as a team, plan Training Dives
Four and Five by appropriately and tor provides. Consider A Good Diver’s Main
accurately accounting for logistics, gas Objective Is To Live and refer back to this
requirements for each diver, OTUs, manual as you plan. Your instructor will
CNS% and maximum depth based on provide the basis for determining your deco
personal SAC rates, dive profiles, gas schedule and have you calculate, OTUs
blends to be used, environmental details
and CNS for each diver and gas, plus gas
and other information provided by the
instructor as necessary about the dives. requirements including one-third reserve,
tank base lines, turn points, equipment
2. Working as a team, think backwards
requirements, logistics, emergency proce-
through either dive (as assigned by
the instructor) from the furthest point dures and other information from the A
imagining realistic problems that might Good Diver’s Main Objective Is To Live
stand between you and surfacing, and planning process. You will perform all cal-
formulate realistic solutions for each, culations by hand, though you may com-
drafting a paper with your list of prob-
pare your results to desk top deco software.
lems and solutions.

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 Although these will be no stop dives, you will plan the dives as
simulated decompression dives. Your plans should contain all infor-
mation you would need to make the dives.
Your instructor will also have you put the “thinking backwards”
principles into practice by having you and your team mates walk
through one of the dives from the furthest point, considering rea-
sonable possible problems and how you would provide solutions to
them. Your instructor will have you write these down to discuss.

Preview: Training Dive Four

Performance Objectives

To successfully complete this training 8. Perform a SAC swim by swimming for

dive, you will be able to: approximately 10 minutes at a level
depth, recording the required infor-
1. Working in a team, plan the dive
mation for subsequent calculation.
following the A Good Diver’s Main
Objective Is To Live procedure, and 9. Deploy a lift bag from the bottom.
perform predive checks following the
Being Wary Reduces All Failures pro- 10. Perform the gas shut down drill
cedure. within 60 seconds (40 seconds if no
isolator valve).
2. Independently don a single deco cyl-
inder at the surface. 11. While in midwater ascending along
a line, switch to the decompression
3. Descend along a line to the bottom, cylinder while following the NO TOX
maintaining control of depth and procedure.
descent speed by adjusting buoyancy.
12. On a line in midwater, simulate
4. Working in a team, perform appro- two decompression stops, one at 6
priate bubble checks and descent metres/20 feet for five minutes and
checks. the next at 5 metres/15 feet for 12
minutes, breathing from the deco
5. Swim for at least two minutes and a
cylinder, and recording required infor-
distance of at least 18 metres/60 feet
mation for subsequent decompression
sharing air with the long hose as both
SAC calculations.
the donor and receiver.
13. Independently remove the decom-
6. Independently stage a deco cylinder
pression cylinder at the surface.
following the procedures for correct
staging described previously in this 14. Demonstrate time/depth/gas supply
course. awareness by writing on a slate the
depth and time at the point the diver
7. Independently retrieve and don the
consumes each 35 bar/500 psi of
previously staged deco cylinder.
back gas.

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 Predive briefing and gearing up

Training Dive Four

• Note the time and depth at the point you reach each 35 bar/500
psi consumed.
Entry — appropriate for environment
Weight check (if needed)
Bubble check
Don deco cylinder at surface
Descent
Descent check

THREE
Remove deco cylinder and stage it on bottom.
Long hose drill
Retrieve cylinder
SAC swim — return to ascent line
Deploy lift bag from bottom
Gas shut down drill
Free time in general area for experience and practice
Ascend line — NO TOX switch to deco bottle
SAC deco
Surface — remove deco cylinder at surface
Recheck weight (if necessary)
Exit

Post Dive
Performance review
Disassemble and stow equipment
Log dive for instructor signature.

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 Preview: Training Dive Five

Performance Objectives

To successfully complete this training 8. Complete the gas shutdown drill

dive, you will be able to: within 45 seconds.
1. Working in a team, plan the dive 9. Deploy a lift bag from the bottom as
following the A Good Diver’s Main a team, and ascend six metres/20 feet
Objective Is To Live procedure, and along the lift bag’s line.
perform predive checks following the
Being Wary Reduces All Failures proce- 10. Switch to the appropriate deco cyl-
dure, the bubble checks and descent inder following the NO TOX proce-
checks. dure and use it to make a simulated
three minute decompression stop
2. Independently don two deco cylinders at 9 metres/30 feet and six minutes
at the surface. at 6 metres/20 feet, while recording
required information for subsequent
3. Descend along a line to the bottom,
decompression SAC calculations.
maintaining control of depth and
descent speed by adjusting buoyancy. 11. From a simulated decompression
stop at 6 metres/20 feet using a
4. Remove and stage two deco cylinders
decompression cylinder, ascend to 5
on the bottom following the previ-
metres/15 feet and switch to another
ously described procedures.
decompression cylinder following
5. Swim 10 metres/30 feet sharing gas the NO TOX procedure, and make a
with the long hose as a donor with simulated deco stop for 14 minutes,
a mask, and as a receiver without a recording required information for
mask. subsequent decompression SAC calcu-
lations.
6. Retrieve and don two deco cylinders
following the previously described 12. Independently remove two decom-
procedures. pression cylinders at the surface.
7. Swim for approximately three minutes 13. Demonstrate time/depth/gas supply
at an accelerated pace, as though awareness by recording on a slate the
fighting a mild current, recording the depth and SPG reading at each 12
required information for subsequently minutes throughout the dive.
calculating SAC rates for higher-than-
normal exertion.

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 Predive briefing and gearing up

Training Dive Five

• Record depth and SPG reading at each 12 minute interval
throughout the dive.
Entry — appropriate for environment
Weight check (if needed)
Bubble check
Don deco cylinders at surface
Descent
Descent check

THREE
Remove deco cylinders and stage them on bottom.
No mask long hose drill
Retrieve cylinders
SAC faster swim — return to ascent line
Gas shutdown drill
Free time in general area for experience and practice
Deploy lift bag from bottom
Ascend lift line bag 6 metres/20 feet line
Ascend main line — NO TOX switch to first deco bottle
SAC deco
Ascent to 5 metres/15 feet, NO TOX switch to second deco bottle
— 14 minute stop with SAC deco and air break practice
Surface — remove deco cylinders at surface
Exit

Post Dive
Performance review
Disassemble and stow equipment
Calculate individual SAC rates
Log dive for instructor signature.

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 Computer (Continued)
As you learned, you back up a multigas computer with a single
gas computer by setting the single gas computer for your back gas.
Decompress as if using back gas, with the higher oxygen blends for
conservatism. That’s pretty straightforward.

How Do I Figure 1.5 Times With a Computer?

S
upposed you’re following a computer based total deco time remaining), you determine by
decompression and have to follow the pro- noting the beginning and ending elapsed bottom
cedure for extending the 6 metre/20 foot time.
and final stops by 1.5 because you had to assist
After you complete that, ascend to the final stop
a team mate and went above your stop depth
for 1.5 times the remaining deco time you noted
for two minutes. The problem is that when you
on your slate.
overstay the 6 metre/20 foot stop, the computer
shortens what it predicts for your final stop (5 Example: You’re following the procedure and
metres/15 feet or 3 metres/10 feet) — but, you your elapsed bottom time is 56 minutes when
need to stay for 1.5 times the original time. you reach 6 metres/20 feet. At 66 minutes, the
computer clears you to the final stop and shows
Do this: Stay at your 6 metre/20 foot stop
24 minutes of decompression remaining. You stay
until the computer clears you to the last stop.
at 6 metres/20 feet for an additional five minutes
Immediately note the decompression time
(1.5 x 10 minutes). Then ascend to the final stop
remaining on your slate, and the elapsed bot-
for 36 minutes (1.5 x 24 minutes).
tom time, but do not ascend. Instead, stay at 6
metres/20 feet until you complete the 1.5 times Note: Some computers automatically calculate
the 6 metre/20 foot stop time, which either the missed deco stop procedures. See the manufac-
computer tells you, or if not (some only show turer’s instructions.

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 Instructor Guide 40 Handouts Tec Deep Diver
Digital Manual

Appendix

Other Delivery Content Hand Outs

Tec 40
Other Delivery Content, Tec 40-1
Study assignment: Tec 40 Handout 1

Learning Objectives
By the end of this section, you should be able to answer these questions:
1. How do the Tec 40, Tec 45 and Tec 50 courses fit together as the overall DSAT Tec Diver
course?
2. What are the general goals of the Tec 45 and Tec 50 courses?
3. What are the limits of your training as a Tec 40 diver?

G. The DSAT Tec Diver course

1. The Tec 40 course is the first of three subcourses that together make up the
DSAT Tec Diver course.
a. The DSAT Tec Diver course was originally called the Tec Deep
Diver course (hence the Tec Deep Diver Manual).
b. The three subcourses, in order are the Tec 40, Tec 45 and Tec 50
courses. The names reflect the maximum qualification depth in
metres for the respective levels.
c. Completing all three qualifies you as a Tec 50 diver (formerly Tec
Deep Diver), which is a fully qualified, open circuit entry level
EANx deep decompression technical diver.
2. Tec 45 general goals are to train certified Tec 40 divers
a. to use full technical equipment.
b. to make decompression dives to 45 metres/145 feet using air or
enriched air, with accelerated decompression techniques.
c. to dive with one decompression gas with up to and including 100
percent oxygen.
3. Tec 50 general goals are to train certified Tec 45 divers
a. to make decompression dives to 50 metres/165 feet using air or
enriched air, with accelerated decompression techniques.
b. to dive with two decompression gases with up to 100 percent oxygen.

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H. Certification as a Tec 40 diver qualifies you to dive within the following limits, applying
the appropriate procedures and equipment as you’ve
been trained:
1. Dive to a maximum depth of 40 metres/130 feet using air or enriched air.
2. Make dives with up to 10 minutes required decompression.
3. Use enriched air nitrox with up to 50 percent oxygen (EANx50) during decompres-
sion to make it more conservative.
4. Although your certification qualifies you to these limits, you must also consider
other limitations, such as the environment, conditions and other factors, and apply
more conservative limits when planning dives.
5. These limits apply, even if you complete the Tec 40 using double cylinders and
other equipment required for Tec 45 and above.

Exercise, Other Delivery Content, Tec 40-1

1. The Tec Diver course (choose all that apply)
q a. consists of three subcourses.
q b. begins with the Tec 40 subcourse.
q c. no longer exists.
2. The Tec 50 course qualifies a diver to make dives
q a. with up to 50 minutes decompression.
q b. with deco stops as deep as 50 feet/12 metres
q c. to a depth of 50 metres/165 feet
q d. to a depth of 50 fathoms (300 feet).
3. As a Tec 40 diver, applying appropriate procedures and equipment as you’ve been trained,
you’re qualified to (choose all that apply)
q a. to dive as deep as 40 metres/130 feet.
q b. have up to 10 minutes required decompression.
q c. use a single gas with up to 50 percent oxygen during decompression.
How did you do?
1. a, b. 2. c. 3. a, b, c.

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Other Delivery Content, Tec 40-2

Study assignment: Tec 40 Handout 2

Learning Objectives
By the end of this section, you should be able to answer these questions:
1. Why can the equipment requirements for Tec 40 be less stringent than the standardized
technical rig?
2. What are the guidelines for selecting masks, fins and snorkels for the Tec 40 level?
3. What characteristics do you look for cylinders and cylinder valves for the Tec 40 kit?
4. What is the minimum number of fully independent regulators, per diver, and how do you
configure each?
5. What type of BCDs can you use for Tec 40 level diving? Why is a tec diving harness rec-
ommended?
6. How do you choose an appropriate exposure suit for technical diving?
7. What are your options regarding weight systems, and what are the advantages and disad-
vantages of each?
8. What types of dive computers and other instruments do you need for Tec 40 level diving?
9. What types of cutting tools are appropriate for deep technical diving, and how many
should you have?
10. What are six general guidelines regarding pockets, accessories and clips you might need
when technical diving?
11. What is a “stage/deco cylinder”?
12. How do you set up a stage/deco cylinder?
13. Why might you need a lift bag/DSMB and reel on a technical dive?
14. What are suitable lift bags/DSMBs and reels, and how do you secure them on your rig?
15. What are four recommendations regarding equipment maintenance?
You should also be able to:
16. Describe the layout, arrangement and configuration of the basic Tec 40 rig, with options,
from head to toe as worn by a Tec 40 diver.

A. Tec 40 equipment requirements and the standardized technical rig

1. The technical diving community has a generally accepted open circuit
equipment configuration as worn on a technical deep dive. This standardized
technical rig employs all required equipment in a streamlined configuration
based on a philosophy that minimizes confusion and procedural error. The
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standard technical rig (backmount or sidemount) is required at the Tec 45 level

and beyond.
2. You can dive with a less stringent equipment configuration (i.e., the Tec 40 kit or
rig) within Tec 40 limits because the depth and decompression time limits are
very restricted compared to broader technical deep diving.
a. Exceeding Tec 40 limits (40 metres/130 feet and up to 10 minutes total
required decompression) is not acceptable or reasonable with the Tec 40
rig.

B. Mask, fins and snorkel

1. Generally, the mask and fins you use for recreational scuba diving in a given
environment are acceptable for the Tec 40 rig.
a. Full sized fins (appropriate to your size) are generally recommended.
b. Secure/tape loose straps so they don’t dangle and can’t slip.
c. Spring heel fins (in place of straps) are good options because they’re very
strong, nothing dangles and they don’t need adjustment and are easy to
don and remove.
2. Snorkels are optional, but generally recommended for the Tec 40 rig.
a. They allow you to breathe at the surface without using gas from your
cylinder.
b. They can be slightly cumbersome in an air sharing situation, so you may
want to carry a folding/collapsible model in your pocket.

C. Cylinders and valves

1. You generally want a high capacity cylinder as your primary cylinder with the
Tec 40 kit. This is because you use more gas on a deeper dive, and you need to
keep a larger reserve.
2. 11-12 litre/71.2-80 cubic foot cylinders are generally considered the minimum
size – larger (18 litre/100 cubic foot+ ) cylinders are preferred, but not readily
available in some locations.
a. If you opt for double cylinders, you should wear the standardized techni-
cal rig, not the Tec 40 kit.

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3. The cylinder should have an H or Y valve, which allows you to have two
entirely separate regulators. In case of a failure, you can shut down the gas
to either one and still access the remaining gas with the other.
a. With Tec 40 limits, it is alternatively acceptable to have a large, main
cylinder with a pony bottle in place of an H/Y valve.
b. If you use a pony instead of an H/Y valve, it should have a capacity
of 850 litres free gas/30 cf or larger.
c. The pony usually has the same gas (EANx blend or air) as the main
cylinder. If it has a higher oxygen content, the gas must still be
breathable at the deepest planned depth (max 1.4 ata/bar), with
a margin for error.
4. The DIN (Deutche Industrie Norm) threaded system for valve apertures is
generally preferred to the yoke system in tec diving.
5. Valve caps should not be tied to valves as they commonly are in recreational
diving. Remove completely when diving.

D. Regulators
1. Because you cannot immediately surface, tec diving always requires a mini-
mum of two fully independent regulators per diver (does not count those on
stage or decompression cylinders).
2. Choose top of the line, balanced regulators for maximum reliability and per-
formance at depth.
3. Configure the regulator that goes on the right valve post with a low pressure
inflator hose and second stage with a two metre/seven foot hose.
4. Configure the regulator that goes on the left valve post with the SPG and a
second stage on a standard length hose (about 80 cm/32 inches). If using a
dry suit or a double bladder BCD system, this regulator also has a low pres-
sure inflator hose.
a. If using a pony bottle instead of an H valve, both regulators have
SPGs. In this case, the SPGs must be clearly marked or secured to
avoid any confusion.
5. Neither regulator has two second stages.
6. The DIN connection system is preferred (most DIN regulators accept adapt-
ers for yoke use).

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E. BCD and harness

1. Most BCDs with shoulder and hip D-rings (other suitable attachment hard-
ware in those locations) can be used for a Tec 40 rig. The D-rings are neces-
sary for your decompression cylinder.
2. A tec diving harness configured for a single cylinder is generally recom-
mended, though not essential, for the Tec 40 kit.
a. Tec harnesses are harnesses that mount on top of an interchangeable
BCD bladder. There are rigid plate (steel, aluminum or plastic) and
all fabric versions.
b. Tec harnesses have crotch straps, adjustable shoulder and waist
D-rings and other features suited to higher level tec diving.
c. The tec harness is recommended because you will use it when you
move on to the Tec 45 course, and because you can use a double
bladder BCD (BCD with two independent bladders and inflation/
deflation systems) so you have backup buoyancy control.
• In a decompression situation, simply dropping weights to
restore buoyancy may not be an option because you would
have too much buoyancy to maintain a decompression stop.
• Planning for BCD failure must be part of planning any
technical dive. The double bladder BCD is the simplest,
most reliable option.
• The Tec 40 rig (single cylinder) is not as negatively buoyant
as higher level tec rigs, so redundant buoyancy is not manda-
tory at this level.

F. Exposure suits
1. Choose your exposure suit based on the water temperature at depth and the
dive duration.
2. Tec dives tend to be longer than recreational dives, calling for more expo-
sure protection. You also don’t exert and generate much heat while decom-
pressing.
3. Dry suits offer the longest durations and coldest water protection.
a. They may provide ample backup buoyancy.
b. You should master dry suit diving as a recreational diver before
using a dry suit for technical dives.

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• 20 dry suit dives is a conservative minimum before tec diving dry.

• In recreational diving, you only use your dry suit for buoyan-
cy control while underwater.
• In tec diving, you typically add gas to the suit to avoid a suit
squeeze and use your BCD. This means controlling the gas in
both your suit and BCD – a more complex skill to master.
4. Wet suits are adequate in warmer waters and well suited to dives within
Tec 40 limits.
a. A full 6 mm/.25 in wet suit with hood will generally handle dives up
to two or three hours (far longer than a Tec 40 dive) in water
24ºC/75ºF or warmer.
b. In a heavy rig, you need a double bladder BCD or other means for
reliably handling a BCD failure.
c. The advantage of a wet suit over a dry suit is operational simplicity –
you only need to adjust your BCD.

G. Weight systems
1. Except in very warm water requiring minimal exposure protection, you will
usually need weights even in a technical rig. A weight belt, integrated
weights or a weight harness are acceptable.
a. Some tec divers choose a metal plate harness to reduce the amount
of lead they need to wear.
2. Weight belt
a. Advantages: simple, readily available when needed
b. Disadvantages: with crotch strap, must don after putting on rig so it’s
not trapped.
3. Integrated weights
a. Advantages: no need to put on last, positioned amid rig
b. Disadvantages: must have BCD/harness system with weight system
build in; makes overall scuba rig heavier
4. Weight harness
a. Advantages: put on before scuba rig, doesn’t add to rig’s weight
b. Disadvantages: may be awkward to adjust rig so it doesn’t interfere
with quick release weight ditching.

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5. Loss of weights can be significant hazard on a decompression dive because

it can make it difficult or impossible to stay at stop depth.
a. Some tec divers put two quick release buckles on weight belts to
avoid accidental loss.
b. Another option is to wear a crotch strap over a weight belt to avoid
accidental loss. With this approach, it’s recommended that the crotch
strap have a quick release so the weights can be discarded
if necessary.

H. Instrumentation
1. You need two ways of determining your decompression requirements.
a. The simplest option is to wear two dive computers.
b. The second option is to wear a computer with depth gauge, timer and
decompression tables.
2. For Tec 40, you only need a standard air dive computer or computers.
a. An EANx compatible computer is recommended – allows you to
benefit from more bottom time with enriched air, and calculates your
oxygen exposure.
b. If you have yet to invest in your dive computers, choose models that
run multiple gases and trimix so you’ll be set for Tec 45 and beyond.
3. Arm mounted instruments (other than SPG) are generally preferred (required
at the Tec 45 level and up).
4. Mechanical SPGs are generally preferred because they’re simple and reliable.
5. Compass – You need a high quality, liquid filled model if using a standard
compass. Many newer dive computers have electronic compasses. The
compass is commonly carried in a pouch or pocket until needed.

I. Cutting tools
1. You should have a cutting tool, and ideally two (two required at Tec 45 level
up). Mount at least one where you can reach it with either hand (generally
waist/chest area).
2. Typical dive knife, dive shears, Z-knife (hook with blade), stainless folding
knives and dive tools are all acceptable.
3. Large, calf-mounted knives/tools are generally avoided in tec diving, espe-
cially cave diving and wreck penetration, because they entangle easily.

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J. Guidelines for pockets, accessories and clips

1. Avoid large pocket pouches on harnesses – they cause too much bulk and
clutter.
2. Most useful pockets in tec diving are thigh pockets on your exposure suit.
3. Mount stainless steel or brass clips on accessories to clip to your BCD or
harness. Don’t mount the clips on the BCD or harness.
4. Sliding gate clips (a.k.a. dog clips) are preferred to marine snaps (swinging
gate clips), because they won’t accidentally clip to things by themselves.
5. Choose clips based on the environment – you need larger clips when wear-
ing thick gloves.
6. Using and mounting clips
a. When possible, keep accessories in pockets until needed.
b. Clip accessories well out of the way, secured so they don’t dangle.
c. Attach clips so they can break away so you can release in an emer-
gency. The simplest approach is to mount the clip via a small o-ring
or thin pull tie that breaks with a sharp tug.

K. Stage/deco cylinders
1. A stage cylinder is used to extend the deep portion of the dive. A deco
(decompression) cylinder provides gas (usually with higher oxygen content)
during decompression. They are rigged the same, so it’s common to call
deco cylinders “stages” or “stage cylinders.” The general term for both is
“stage/deco cylinder.” In context, the terms are seldom confusing.
2. Stage/deco cylinders are worn on the side under the arm, clipped at the
waist and on the chest.
3. A stage/deco cylinder never replaces one of the two regulators/valves
you need from your primary gas supply.
4. As a Tec 40 diver, you will often use a deco cylinder.
a. Some dives at this level do not need a deco cylinder, because you
have enough gas, plus your required reserve, for the entire dive
including decompression.
b. But, a deco cylinder is recommended nonetheless because it provides
extra gas capacity, plus gives you the option of switching to EANx
with a higher oxygen content for added decompression conservatism.
(More about this later).

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5. Typical stage/deco cylinder setup

a. The cylinder is typically a 4 litre/30 cf size or larger. The popular
aluminum 11 litre/80 cf has more capacity than you usually need at
the Tec 40 level, but it is commonly available and easy to handle.
It is perfectly acceptable to use – having too much gas is seldom
an issue.
b. The cylinder has a nylon rope/strap approximately 46 cm/18 in,
approximately under the valve opening, running down to a band
around the cylinder with a clip at each end. This serves as a handling
strap; the clips attach the cylinder on your BCD D-rings at the waist
and chest/shoulder.
c. The regulator has a single second stage and SPG. Hoses tuck under
inner tubing, bungee or stretch nylon straps around cylinder.
d. The second stage has break-away clip usually attached to the hose
close to where it meets the second stage.
e. The SPG may have a very short hose, or a standard length hose that
is tucked along the cylinder length.
f. It’s recommended that the clips be attached via rope or nylon so you
can cut the cylinder free if a clip jams.
g. For safety, stage/deco cylinders are always clearly marked with
the gas blend they contain, the maximum depth you can breathe
the gas (based on the oxygen partial pressure) and the diver’s
name. These markings are always large and positioned so a team
mate can read them while the cylinder is worn.

L. Lift bags/DSMBs (Delayed Surface Marker Buoys) and reels

1. You may find yourself accidentally away from your planned ascent line
(anchor/mooring line).
2. In this case, your team uses a reel to deploy a lift bag or DSMB. This gives
you an ascent reference, allows surface support personnel to track your posi-
tion, and helps you maintain your decompression stop in midwater.
3. Suitable lift bags are brightly colored, with large capacities (45 kg/100 lbs
lift) preferred. DSMBs are taller and more compact; they don’t have to have
the same lift capacities. Preferred DSMBs have one-way valves for filling,
with overpressure valves. These keep the buoy inflated even if it topples at

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the surface momentarily. It is recommended that you write your name on

your lift bag/DSMB for surface support identification.
4. Lift bags are carried rolled up and tucked into special carrying pockets or
put in bungees that stow them horizontally in the small of the back. DSMBs
roll up more compactly, generally, and fit in harness/BCD pockets or thigh
pockets.
5. A suitable reel is compact with ample line to reach the surface.
6. The reel is clipped to a D-ring on the right hip.

M. Maintenance
1. You rely on your gear for life support. Therefore, maintain it according to
manufacturer recommendations.
2. Have regulators, valves, BCDs and gauges inspected and overhauled at least
annually, or more frequently for heavy use or as manufacturer specified.
3. Have anything that doesn’t appear to work normally serviced before using it.
4. Never tec dive with gear in anything but top shape and within its design
parameters. To do otherwise needlessly raises your risk of injury or death by
starting the dive with a potential problem.

N. Putting it together: basic Tec 40 rig, head to toe

1. Use a cylinder with H or Y valve in a BCD/tec harness.
2. The left side regulator has a short hose second stage. This is the secondary
regulator. It routes to the right and hangs below the chin on a bungee. The
SPG hose goes down along the cylinder; the SPG has a clip to secure it to
waist or chest D-ring (as preferred). Low pressure hose(s) feeds the dry suit
and/or backup BCD (if used). The valve is open all the way (do not close it
back a quarter turn).
3. The right side regulator has a long hose second stage. This is the primary
regulator. It is the last thing you put in place when kitting up. The hose
routes straight down along the cylinder to the hip, then up across the chest
and around the left side of the neck into the mouth. At the hip, the safety
reel lies on top of it to help keep it in place. The low pressure hose feeds the
primary BCD inflator. There is no SPG. The valve is open all the way (do
not close it back a quarter turn).

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4. If using a pony instead of an H/Y valve, the pony goes on the left side of the
main cylinder and takes the left side (secondary) regulator. In this case, the
right (primary) regulator has the primary SPG, which is clipped as described
above. The pony/secondary SPG is clipped low and behind the diver, where
it is retrievable but not easily confused with the primary. It is also clearly
marked (label, color, etc.) to easily distinguish it from the primary SPG.
5. With double bladder BCDs, the backup inflator is secured behind the diver
so that it is easy to deploy, but not easily confused with the primary (you
only use one BCD bladder at a time).
a. Some divers leave the LP hose disconnected from, but bungeed to
the backup inflator. This avoids accidental inflation (leaking inflator
valve), but is easily connected for use.
6. Instruments are ideally arm mounted (except SPG), though compact con-
soles are acceptable in the Tec 40 rig.
7. The weight system is secure, free for ditching. The backup buckle is secured if used.
8. Mask and fins are preadjusted and inspected, secured so they can’t slip out
of adjustment.

Exercise, Other Delivery Content, Tec 40-2

1. Tec 40 has less stringent equipment requirements than the standardized technical rig,
because the limits of Tec 40 diving keep you within recreational depth limits and a rela-
tively short decompression time.
q True
q False
2. You cannot use the same fins you use in recreational diving for Tec 40 diving.
q True
q False
3. The recommended valve type for the Tec 40 kit is
q a. the standard yoke valve.
q b. a J reserve valve.
q c. an H or Y valve, DIN system.
q d. a J or K valve, yoke system.

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4. The minimum number of fully independent regulators, per diver, is

q a. 1
q b. 2
q c. 3
q d. 6
5. You can use any BCD with D-rings or attachment hardware at the shoulder/waist for the
Tec 40 kit.
q True
q False
6. Choose an exposure suit for a tec dive based on __________. (choose all that apply)
q a. depth
q b. duration
q c. temperature
q d. activity level
7. You never use a weight belt while tec diving.
q True
q False
8. For the Tec 40 level, a single computer is all the instrumentation you need.
q True
q False
9. At the Tec 40 level, you should have at least one cutting tool, but it’s recommended you
have two.
q True
q False
10. General guidelines regarding pockets, accessories and clips include (check all
that apply):
q a. mount clips to the accessories.
q b. attach clips so they can break away.
q c. thigh pockets on your exposure suit are a good option.
q d. marine (swing gate) clips are the best choice.
11. At the Tec 40 level, a stage/deco cylinder will be used to
q a. carry a decompression gas.
q b. carry gas to extend the deepest portion of the dive.
q c. both a or b.
q d. None of the above.

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12. A stage/deco cylinder is always marked with the gas it has in it, the maximum depth
and the diver’s name.
q True
q False
13. You may need a lift bag/DSMB and reel
q a. as a backup BCD.
q b. in case you lose track of your ascent point.
q c. to open a shipwreck hatch
14. A suitable lift bag or DSMB should have ample lift and be blue or gray.
q True
q False
15. Never, ever tec dive with gear that’s in anything less than top shape.
q True
q False
16. The primary regulator (choose all that apply)
q a. goes on the right.
q b. has a long hose second stage.
q c. has the primary BCD low pressure hose.
q d. goes on the left.

How did you do?

1. True. 2. False. The same fins you use recreational diving are usually suitable for the Tec
40 level. 3. c. 4. b. 5. True. 6. a, b, c, d. 7. False. A weight belt is a common option in tec
diving. 8. False. You need at least two computers, or one computer and a depth gauge,
timer and decompression tables. You should also have SPGs and a compass. 9. True. 10.
a, b, c. 11. a. 12. True. 13. b. 14. False. It should be red, yellow or some other bright
color. 15. True. 16. a, b, c.

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Other Delivery Content, Tec 40-3

Study assignment: Tec 40 Handout 3

Learning Objectives
By the end of this section, you should be able to answer these questions:
1. What is the maximum oxygen blend you would use as the bottom gas for a dive to 40
metres/130 feet?
2. What is the maximum percentage of oxygen you will use as a Tec 40 diver?

H. As a Tec 40 diver, your maximum allowable depth is 40 metres/130 feet.

1. Using the maximum depth tables on pages 266 and 267, you find that
EANx28 is the highest oxygen content gas blend you can use at 40
metres/130 feet (PO2 = 1.4 ata/bar).
2. You may use blends with more oxygen, but at increasingly shallower maxi-
mum depths.
3. With blends that have 36 percent or more oxygen, your maximum depth is
so shallow and your no decompression time is so long that you probably
won’t have to make decompression dives at all.
I. The maximum oxygen percentage you’re qualified to use as a Tec 40 diver is 50
percent (EANx50). You will normally use this as a decompression gas (you can use
it as a bottom gas, but the maximum depth is 18 metres/59 feet – you will probably
not need to decompress on such a dive).
1. The maximum depth for using EANx50 as a decompression gas (PO2 = 1.6)
is 21m/70 ft (See the Equivalent Air Depth and Oxygen Management Tables
for 50% on pgs 274 & 288)

2. You may be carrying EANx50 (or other deco gas) to a depth deeper than
you can safely breathe it. It is critical to follow all gas handling proce-
dures to avoid accidentally switching to it at too deep a depth. You will
learn and practice these procedures beginning with Tec 40 Training Dive One.

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Exercise, Other Delivery Content, Tec 40-3

1. The maximum oxygen enriched air you would use as bottom gas for a dive to 40
metres/130 feet is
q a. EANx28.
q b. EANx32.
q c. EANx36.
q d. EANx50.
2. The maximum oxygen content enriched air that you’re qualified to use as a Tec 40 diver is
q a. EANx28.
q b. EANx32.
q c. EANx36.
q d. EANx50.

How did you do?

1. a. 2. d.

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Other Delivery Content, Tec 40-4

Study assignment: Tec 40 Handout 4

Learning Objectives
By the end of this section, you should be able to answer these questions:
1. What is a “bounce” dive?
2. Why is it recommended that you switch to a higher oxygen EANx for decompression
without accelerating your decompression, and/or set your dive computer for an EANx
with less gas than actual, if making a “bounce” technical dive?

E. “Bounce” dives
1. A short dive to any depth is called a “bounce” dive.
a. The definition is imprecise – what one person calls a bounce dive
another may not.
b. It is possible to make dives within the scope of Tec 40 qualifications
that some would be consider bounce dives.
2. There are some anecdotal concerns about bounce decompression dives
a. Some people think DCS data indicate that short, deep dives with
short decompression requirements have a higher DCS risk than
would be expected based on decompression models
b. Again, definitions of “short” and “deep” and “risk” are subjective in
this context.
c. The concerns are hypothetical and not quantified, but they exist
nonetheless.
3. To minimize bounce dive concerns (at all levels):
a. Plan your dive with your computer set for air or an EANx with less
oxygen than you actually use.
b. Use a single gas computer, or if using a multigas computer, leave it
set for your bottom gas, but decompress with an EANx blend with
more oxygen.

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c. Either of these (or both) will make your decompression more

conservative.
• The required decompression time for a short, deep dives is
correspondingly short. Deco is so short there is no meaning-
ful benefit to accelerating decompression. Instead, you use
EANx to make your decompression more conservative
instead of shorter.
• It is common to extend the last deco stop two or three min-
utes as well.

Example: You dive to 40 metres/130 feet. You leave your dive com-
puter set for air, but you actually dive using EANx25 as your bottom
gas. You decompress with EANx40, but you leave your dive comput-
er (if it is a multigas model) set for air during
decompression.

d. You will plan your dives as a Tec 40 diver based on decompressing

as if using your bottom gas, but using EANx to make your decom-
pression more conservative.

Exercise, Other Delivery Content, Tec 40-4

1. A “bounce” dive isn’t defined precisely, but means a short dive to any depth.
q True
q False
2. To minimize bounce dive concerns (choose all that apply):
q a. set your dive computer for air or EANx with less oxygen than the gas you
actually use.
q b. accelerate your decompression.
q c. decompress with a gas that has more oxygen than you set your computer for.
q d. ascend rapidly to minimize your time at depth.

How did you do?

1. True. 2. a, c.

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Other Delivery Content, Tec 40-5

Study assignment: Tec 40 Handout 5

Learning Objectives
1. How do you use desk top decompression software to plan a decompression dive based on
a single gas, with no more than 10 minutes of decompression and a maximum depth of
40 metres/130 feet?
2. How do you use decompression software to determine your gas supply requirements?
3. What is the minimum reserve gas you should have on a technical dive?
4. How do you set your dive computer to follow the plan you made with your decompres-
sion software?
5. How does your team stay together when using dive computers to provide decompression
information?
6. What limits tell you it is time to end your dive?
7. How do you calculate turn pressure?
8. How do you account for your oxygen exposure when using a gas with a higher oxygen
content than you set your dive computer for?
9. What do you do if your desk top decompression software and dive computer differ signif-
icantly in their decompression information, or if your gas requirement calculations
appear to be off?

A. Starting with Tec 40 Practical Application Two, you’ll begin planning decompres-
sion dives using desk top decompression software.
1. Your dive planning will continue throughout the course and be the basis for
simulated and actual decompression dives you make.
2. The methods you learn also form the foundation for all your subsequent
technical dive planning. However, gas and decompression planning becomes
more complex as you go deeper and have longer decompression.

B. You will follow these basic steps:

[Note: Your instructor will take you through this, step by step, during Tec 40
Practical Application Two, followed by you and your team mates planning a dive.]
1. Launch the desk top decompression program (may be iPhone or PDA based
as long as it provides decompression and gas supply calculations, as well as
the ability to choose different gases).
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2. Set the dive characteristics and presets.

a. Select metric or imperial, open circuit (not closed circuit rebreather).
b. Working and decompression SAC rates
• You will determine your working (bottom) SAC rate during
Tec 40 Practical Application Two based on the data you gath-
ered during Tec 40 Training Dive One.
• You will gather decompression SAC rate data during Tec 40
Training Dive Two. In the meantime, use 2/3 thirds your
working rate.
• Your program may refer to SAC as RMV.
c. Select the single gas you want to use for decompression calculations
• You will probably use an EANx blend for bottom gas.
• Use the Maximum Depths tables in the Tec Deep Diver
Manual to find the highest oxygen percentage for the EANx
to your planned depth (PO2 1.4)
• Set the program for the EANx blend you will use, or for one
with lower oxygen. At the Tec 40 level, it is simplest to set
for air most of the time (21%).
• You will probably use another EANx with higher oxygen for
decompression. Do not set the program for this gas at this time.
3. Enter your planned depth and time into the program.
a. Have the computer calculate your decompression. If it is longer than
10 minutes, enter a shorter time, a shallower depth or both.
• Remember, as a Tec 40 diver, your limits are 10 minutes total
decompression time and 40 metres/130 feet maximum depth.
• For simplicity, your dives will be planned as though the
entire dive will be made at the deepest depth. At higher
training levels, however, you will learn to add planned
depth changes.
b. Enter depths/times until the total decompression time required is 10
minutes or less.

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4. Use the program to determine your gas requirements based on your SAC
rates, for the planned dives.
a. Some programs do this each time they calculate decompression.
b. Most programs will show you the gas requirements before and after
calculating your reserve.
c. In technical diving, the standard minimum reserve is 33 percent (rule
of thirds), meaning that one third of all your gas is for emergencies
only. That is, the minimum amount of gas you should have on a dive
1.5 times the amount predicted for the dive and the decompression,
based on your bottom and decompression SAC rates.
d. If your program doesn’t determine reserve, simply multiply the pre-
dicted gas requirements by 1.5 to get the minimum gas volume you
should have with you on your dive.
• If you need a pony bottle or a decompression cylinder to
meet the required minimum volume, it should be at least 1/3
of your total gas supply.
• Note: At higher tec levels (Tec 45 and up), you will calculate
individual gas blends independently and have to have 1.5
times the predicted requirements for each individual gas.
Planning your decompression based on a single gas at the Tec
40 level simplifies this.
e. If the minimum gas volume is greater than the capacity of the
cylinder(s) you have will available, then plan a shorter/shallower
dive until the gas requirements (including reserve) are within the
available capacity.
f. Because divers have differing SAC rates, each diver on the team cal-
culates gas requirements for the team’s planned dive.
• The team works together with the program until arriving at a
depth and time that meets the gas supply requirements for
everyone.
• A common strategy is to plan the dive based on the highest
SAC rates (bottom and deco), with all divers carrying the
predicted amount of gas (including reserve). This is accept-
able, because it simply adds reserve for divers with lower
SAC rates.

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g. After you have a final decompression schedule with gas require-

ments that work for the team, print out the decompression schedule
and gas requirements for use at the dive site.
• If using only a single computer, print out backup tables to
laminate (or list them on a slate) and use with a timing device
and depth gauge in the event of computer failure. It is recom-
mended that you print schedules for your planned depth and
time, as well as plus and minus five minutes and plus and
minus 3 metres/10 feet (nine schedules total).
5. During equipment setup for the dive, set your dive computer(s) for the
EANx blend or air that you used in the decompression software.
a. Your actual EANx blend may have a higher oxygen content, provided
you don’t exceed a PO2 of 1.4 at your deepest depth.
b. Your decompression cylinder may have EANx50 (or a blend with
less oxygen). Do not decompress with it at a depth where the PO2
exceeds 1.6.
c. These gases with higher oxygen content simply make your decom-
pression more conservative.
d. During the dive, you and your team mates may have slightly differ-
ent decompression schedules due to slight variances in your depths,
as well as differences in your dive computer’s decompression models.
• To stay together, the team stays at each stop until all computers
clear all divers to ascend to the next stop or surface.
• If using tables (back up situation), team stays at each stop
until all computers clear all divers to ascend, or for the table
stop time, whichever is longest.
6. Limits that end the dive.
a. In technical diving, your dive ends when anyone on your dive team
reaches any of the following, whichever comes first:
• you reach the planned bottom time (what you used in the
decompression software)
• your or a team mate’s dive computer shows 10 minutes
decompression time required (or less if the planned decom-
pression was less)

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• It is important to turn the dive with the planned

decompression time showing, even if the bottom time
is less than planned and the required decompression is
still less than 10 minutes, because your decompression
gas volume requirement is based on the planned
decompression time.
• you or a team mate reaches turn pressure on your gas supply
7. Turn pressure is the reading on your SPG that indicates it is time to head up.
It is calculated based on the cylinder pressure of the gas volume your soft-
ware predicts you’ll use on the bottom. Knowing your turn pressure and
having it written on a slate assures that you head up with the gas for decom-
pression and reserve intact.
a. Almost all software will tell you the required gas for all individual
gases, but many do not tell you how much you use on the bottom, or
calculate turn pressure.
b. To determine your turn pressure, you may therefore have to do so
with a calculator and the tables in the Tec Deep Diver Manual.
c. You will use turn pressure formulas, as well as what you already
learned about SAC and actual gas supplies in Tec 40 Knowledge
Development One.
• Note: For simplicity, treat your descent as time on the bot-
tom. This gives you a slightly higher reserve.
d. Formulas:
• Metric: Turn pressure = start pressure – (bottom volume ÷
cylinder capacity)
• Imperial: Turn pressure = starting pressure – (bottom volume
÷ baseline)
e. Examples

Metric example:
Your working SAC rate is 19 litres per minute. You plan a dive to 40 metres
for 10 minutes. Your decompression software shows that using an 11 litre
cylinder, working pressure 205 bar, and a 9 litre deco cylinder will provide
the gas volume you need. By what pressure should you start your ascent?

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First, find your bottom volume.

Bottom volume = minutes X SAC X conversion factor

Bottom volume = 10 X 19 X 5.2

Bottom volume = 988 litres

Assuming your 11 litre cylinder is full (205 bar), then:

Turn pressure = 205 – (988 ÷ 11)

Turn pressure = 115 bar

To manage your gas appropriately, you should begin ascending when or

before your SPG reaches 115 bar.

Imperial example.

Your working SAC rate is .8 cf per minute. You plan a dive to 130 feet for
10 minutes. Your decompression software shows that using an 80 cubic foot
cylinder, working pressure 3000 psi, and a 65 cubic foot deco cylinder will
provide the gas volume you need. By what pressure should you start your
ascent?

First, find your bottom volume.

Bottom volume = minutes X SAC X conversion factor

Bottom volume = 10 X .8 X 4.9

Bottom volume = 39.2 cubic feet

Next, find the baseline for an 80 cubic foot cylinder. Recall that to get the
baseline, you divide the working capacity by the working pressure

Baseline = cap ÷ working pressure

Baseline = 80 ÷ 3000

Baseline = .0267
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Assuming your 80 cubic foot cylinder is full (3000 psi), then:

Turn pressure = 3000 – (39.2 ÷ .0257)

Turn pressure = 1474 psi.

To manage your gas appropriately, you should begin ascending when or

before your SPG reaches 1474 psi.

f. Note that in both examples that your deco cylinder is required to

meet the required reserve (rule of thirds).

C. Oxygen exposure calculations

1. If your dive computer was set for air or EANx with less oxygen than your
actual bottom gas and/or you switched to a higher oxygen decompression
gas for conservatism, you have to account for your oxygen exposure after
the dive, because your dive computer didn’t know how much oxygen you
actually had in your cylinder(s).
2. After the dive, use desktop software and enter the dive as you actually made
it – actual depths, times and gases used. Record your OTUs and CNS clock
for planning subsequent dives.

D. Repetitive dives
1. Plan repetitive dives as you did the first dive, but recall that you must enter
the first dive data and your surface interval so the program can account for
residual nitrogen.
2. When planning a repetitive dive, enter the actual dive as made. You may
also use the previous dive as planned if it yields a more conservative repeti-
tive dive plan.
3. If OTUs or CNS could approach their maximums – unlikely within Tec 40
limits, but possible if you make several repetitive dives – after planning
your dive based on a single gas, enter the planned depths, times and stops
based on the actual gas blends to make sure you will remain within
oxygen limits.

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E. Making software line up with your dive computer

1. After a few decompression dives, you may find that your decompression
software is more conservative than your dive computer, or vice versa.
a. Be sure your backup computer and/or your team mate’s computers
are similar to your computer to rule out a problem with your computer.
2. If you don’t spend the majority of the time at the deepest depth, your dive
computer would be expected to be less conservative than your software,
because it calculates the slower nitrogen absorption. Don’t make any adjust-
ments on this account.
3. If you do spend the majority of the time near the deepest depth, there may
be some difference in the required stops and some variation in the total
decompression time due to minor differences in the decompression models.
This is normal.
4. If there is a large difference between your decompression software and your
dive computers (enough to substantially throw off gas supply calculations
etc.), contact the software author and/or the dive computer manufacturer.
You can adjust safety factors above the default settings to make software
more conservative, but do not make it less conservative unless advised to do
so by the software manufacturer.
5. Assuming no unforeseen emergencies, you should surface from a dive with
your reserve gas supply intact. If you have substantially more or less gas:
a. First, confirm your working and decompression SAC rates. Adjust
your SAC rates in the software if necessary.
b. If your SAC rates are accurate and you’re coming up with a bit less
gas than you should, it is typically that your software predicts less
decompression than does your computer.
c. Check your decompression software setting and adjust it so it is
more conservative and predicts a bit longer decompression.
d. If the decompression seems to be in line (close match between your
dive computer and the software), it may be how the software calcu-
lates gas use. Increase your SAC rate setting even if that makes it
high compared to your calculations.
e. Do not adjust anything if you have too much gas, unless the surplus
is extreme. Too much gas is seldom a problem.

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Exercise, Other Delivery Content, Tec 40-5

1. At the Tec 40 level, the recommendation is that you use EANx for your bottom gas and
set your decompression software dive
q a. for the gas you’re using.
q b. for an EANx blend with more oxygen.
q c. for at least two different gases.
q d. for air or an EANx blend with less oxygen.
2. To determine your gas supply requirements, you must enter your _________ into the
software.
q a. decompression profile
q b. SAC rates
q c. bottom gas
q d. dive computer model
3. The minimum gas reserve you should plan for on a technical dive is ________ of your
total gas supply.
q a. a quarter
q b. a third
q c. half
q d. two thirds
4. At the Tec 40 level, you set your dive computer to follow the plan you made with your
decompression software by setting it for the EANx blend you used for your decompres-
sion planning with the software.
q True
q False
5. When using computers to provide decompression information, the team stays together.
All divers stay at each stop until all computers clear all divers to ascend to the next stop.
q True
q False
6. When you or a team mate reaches any of the following, you should begin your ascent
(choose all that apply):
q a. your planned bottom time
q b. a dive computer shows 10 minutes decompression required
q c. you have a decompression stop at 18 metres/60 feet
q d. turn pressure on your SPG

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7. You calculate turn pressure by determining how much cylinder pressure you would use
for the volume software predicts you will consume on the bottom.
q True
q False
8. To account for your oxygen exposure when using a gas with a higher oxygen content
than you set your dive computer for
q a. you needn’t do anything because the difference is negligible.
q b. you need to dive with a third and fourth dive computer set to the actual content.
q c. you enter the actual dive with the actual gases into your software.
q d. All of the above.
9. If your gas requirement calculations appear to be off, your first step is to confirm your
working and decompression SAC rates.
q True
q False
How did you do?
1. d. 2. b. 3. b. 4. True. 5. True. 6. a, b, d. 7. True. 8. d. 9. True

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Other Delivery Content, Tec 40-6

Study assignment: Tec 40 Handout 6

Learning Objectives
By the end of this section, you should be able to answer these questions:
1. What are Oxygen Tolerance Units (OTUs)?
2. How do you use OTUs to manage oxygen exposure?
3. How do you use the CNS “clock” to manage oxygen exposure?
4. What is the basis for CNS clock surface interval credit?
5. Why may you choose an EANx blend than has a PO2 less than 1.4 at the working depth
for a particular dive?

A. As you already learned, you need to manage your oxygen exposure when using
EANx (and later oxygen as a Tec 45 diver) to avoid pulmonary and CNS oxygen
toxicity.
1. Recall that your primary prevention of CNS toxicity is in keeping your oxy-
gen partial pressure below the critical thresholds of 1.4 (working part of the
dive) and 1.6 (decompression at rest).
2. Because it is a biochemical process, there must be an exposure-time rela-
tionship involved with the onset of CNS toxicity. However, there are so
many other physiological variables involved that, for practical purposes, the
relationship is useless for reliably predicting CNS toxicity.
3. Pulmonary oxygen toxicity does have a useful time-exposure relationship
that allows reliable predictions.
a. OTUs (Oxygen Toxicity Units or Oxygen Tolerance Units, depend-
ing upon the reference) and the “CNS clock” both help you prevent
pulmonary oxygen toxicity.
b. As a Tec 40 diver, pulmonary oxygen toxicity is highly unlikely, but
possible if you make several dives in a short period using EANx
with high oxygen (like EANx50).

B. OTUs
1. OTUs are units that measure your oxygen exposure as a dose. A given time
at a given PO2 yields a certain number of OTUs based on a simple mathe-
matical equation.
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2. At the Tec 40 level, as you know, you use your desk top decompression
software to calculate your OTUs.
a. You enter the actual gases you use (EANx blend) for your bottom
depth and time, and for your decompression stops and times.
3. OTU limits vary depending upon how much diving you’re doing.
a. The Oxygen Tolerance Units Exposure Limits table in the Appendix
of the Tec Deep Diver Manual shows you the limits based on the
number of days diving.
b. The Total OTUs for Mission is the limit for all OTUs together over
the given number of days.
c. The Average OTUs per day is the maximum allowed in a single day.
d. Note that at 11 days on, the daily limit is 300 OTUs.
• Many tec divers use 300 OTUs per day as the limit, even if
diving for fewer than 11 days. This keeps things simple and
conservative.
• You’ll find that 300 OTUs covers a lot of diving – this is a
very workable approach even at higher tec diving levels.
e. Check your OTUs with your desk top decompression software after
each dive.

C. CNS clock
1. It seems somewhat redundant to calculate the “CNS clock” and OTUs, but
this is the state of practice in tec diving.
2. As you know, you calculate CNS clock with your desk top decompression
software. The CNS clock is expressed as a percent of the allowable expo-
sure – so it should not exceed 100 percent.
a. Most software calculates OTUs and CNS clock simultaneously.
3. There is oxygen surface interval credit for the CNS clock.
a. Between dives, your body begins reversing the effects of oxygen
exposure. This means there is potential for crediting time at the sur-
face.
b. The basis for CNS surface interval credit is hospital patients under-
going long term oxygen exposure. The system has a good field
record with use.
c. Most desk top decompression software will credit your CNS expo-
sure when you plan repetitive dives.
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d. The system has variations, so different decompression programs may

give somewhat different results. You can also reference the CNS
Surface Interval Table in the appendix of the Tec Deep Diver
Manual.
e. Note that there is no surface interval credit for OTUs.
4. As always, stay well within CNS and OTU limits.

D. Oxygen exposure and gas blend choice

1. As you’ve learned, the “ideal” blend for a given dive is the one with a PO2
near 1.4 at the maximum depth. This is based on the assumption that you
want the maximum possible oxygen so you have the minimum nitrogen
(and/or helium as a trimix diver) possible.
2. However, previous oxygen exposure or plans for additional dives may affect
this.
3. To keep oxygen exposure well within limits, you may choose an EANx
blend with a PO2 less than 1.4, even if it means a shorter bottom time or a
longer decompression time. This also keeps you well within PO2 limits.
4. As you gain experience and increase your training as a tec diver, it becomes
increasingly important to consider prior and planned dives when determin-
ing your OTUs and “CNS clock” exposure.

Exercise, Other Delivery Content, Tec 40-6

1. Oxygen Tolerance Units are units that measure your oxygen exposure as a dose.
q True
q False
2. To use OTUs, (choose all that apply):
q a. use software to calculate OTUs based on actual depths, times and gases.
q b. stay within the limits of the Oxygen Tolerance Units Exposure Limits table.
q c. never exceed 100 OTUs per day.
q d. use your software to calculate OTU surface interval credit.
3. To use the “CNS clock,” (choose all that apply):
q a. use software to calculate CNS clock percent based on actual depths, times and gases.
q b. you don’t exceed 100 percent.
q c. stay well within limits.
q d. use your software to calculate CNS surface interval credit.

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4. The basis for the CNS clock surface interval credit is extensive testing with military divers.
q True
q False
5. Even if it were available, you may choose an EANx blend with a PO2 less than 1.4 at
the working depth to
q a. make your decompression more efficient.
q b. reduce oxidative wear on your equipment.
q c. decrease narcosis.
q d. manage your oxygen exposure over several dives.

How did you do?

1. True. 2. a, b. 3. a, b, c, d. 4. False. The basis for the CNS clock surface interval credit is
data from hospital patients undergoing long term oxygen exposure. 5. d.

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Other Delivery Content, Tec 40-7

Study assignment: Tec 40 Handout 7

Learning Objectives
By the end of this section, you should be able to answer these questions:
1. As a Tec 40 diver, what should you do if you exceed your planned depth and time?
2. As a Tec 40 diver, what should you do if you have a delay during your ascent?
3. As a Tec 40 diver, what should you if you miss a decompression stop?
4. As a Tec 40 diver, what should you do if you omit decompression?
5. As a Tec 40 diver, what should you do if you run out of gas?

A. This section discusses handling some emergencies within the context of Tec 40
equipment requirements and limits.
1. The same emergencies can be more serious and more complex to handle for
longer, more complex technical dives.
2. This is another important reason to stay within the limits of your training
and equipment.

B. Exceeding your planned depth and time.

1. This should be a rare situation caused by unusual circumstances (if you can’t
control your depth under normal circumstances, you’re not ready to tec dive).
2. Immediately ascend and consult your computer. Your allowable dive time
will likely be much shorter than you planned.
3. If you exceeded your depth significantly and/or for more than a minute, end
the dive immediately.

C. Delay in ascent
1. At the Tec 40 level, a delay in your ascent is not usually a major issue.
2. Your dive computer will calculate the changes in your required decompres-
sion, if any.
3. If using a backup table (computer failed), it is not critical if the delay is
short (2-3 min or less)
a. Don’t count the delay as decompression time.
b. Extend your last stop as much as practicable, gas allowing.

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D. Missed decompression stop

1. At the Tec 40 level, this is most likely to be caused by failure to control
buoyancy.
2. If you can, redescend and complete the stop, plus one minute, then finish
decompression according to your dive computer.
3. If you can’t redescend, stay at the next stop for the combined time of both
stops. Extend your last two stops (if two or more) by 1.5 what your comput-
er requires, and/or as long as you can with the gas you have.
4. Some dive computers will lock up until you redescend to below the depth of
a required stop. They provide no information in the event that you can’t
return to your deeper stop depth. If you have such a computer or computers,
(see the manufacturer’s instructions), you should have your planned decom-
pression schedule with you (on a slate, backup tables, etc.) in case of this
kind of emergency.

E. Omitted decompression
1. Omitted decompression is similar to a missed stop, but involves missing all
required stops and coming all the way to the surface.
2. The risk of DCS is higher than normal, but at the Tec 40 level it should not
be excessive if:
a. you’re using an EANx blend with more oxygen than you’ve set your
dive computers for.
b. you’ve completed most of your decompression using an EANx with
an even higher oxygen content.
3. If you omit decompression for 6 metres/20 feet or less (most likely within
Tec 40 limits), have no symptoms and can return to stop depth in less than a
minute, decompress according to your computer, then extend the last stop as
much as possible.
4. If you omit decompression for 6 metres/20 feet or less (most likely within
Tec 40 limits), have no symptoms and return to stop depth in more than a
minute, extend your 6 metre/20 foot stop by 1.5 times what the computer
requires, and extend the last stop as much as possible.
5. If you omit decompression from deeper than 6 metres/20 feet, return to the
first stop depth. Complete that stop up to and including the 12 metre/40 foot
stop, then extend all subsequent stops by 1.5 times the required decompression.

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6. If you can’t return to depth (no gas available, for instance), breathe oxygen,
remain calm and monitor yourself for DCS symptoms.
7. Some dive computers will lock up if you omit decompression. Others lock
up after a given period (typically a minute), after which they provide no
decompression information. If you have such a computer or computers, (see
the manufacturer’s instructions), you should have your planned decompres-
sion schedule with you (on a slate, backup tables, etc.) in case of this kind
of emergency.

F. The TecRec Emergency Procedures Slate summarizes the procedures for delayed
ascents, missed decompression and omitted decompression. It is recommended that
you carry this slate with you on tec dives.

G. Running out of gas

1. Should be unlikely at the Tec 40 level if you plan your gas supplies correct-
ly and follow the reserve rules.
a. Having a deco cylinder with more than ample gas makes this even
less likely.
2. Increased SAC rate due to exertion is not usually an issue, because you hit
turn pressure sooner, which means a shorter dive time and less decompres-
sion.
3. If you run low on gas in a deco cylinder, switch to your back gas. As a Tec
40 diver, all your decompression should be based on using that gas or ideal-
ly, on one with lower oxygen content.
4. You can share gas with team mates and/or support divers.
5. Generally, if gas termination interferes with your decompression, decom-
press as long as you can, as best as you can. The more you decompress, the
lower your DCS risk. However, do not run out of gas. DCS is serious but
has a high likelihood of successful treatment. Drowning does not.

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Exercise, Other Delivery Content, Tec 40-7

1. If you exceed your planned depth and time, as a Tec 40 diver you should consult your
computer and be prepared to end your dive sooner than planned.
q True
q False
2. If you have a delay during your ascent, as a Tec 40 diver (choose all that apply)
q a. you should decompress for 1.5 times what your computer says.
q b. you should decompress for 3 times what your computer says.
q c. continue to decompress according to what your computer says.
q d. None of the above.
3. If you miss a decompression stop, as a Tec 40 diver (choose all that apply)
q a. you should redescend, complete the stop plus one minute, then finish decompres-
sion according to your dive computer.
q b. surface and seek immediate recompression.
q c. descend to 12 metres/40 feet and extend all stops by 1.5 times what you comput-
er requires.
q d. you may need to refer to your written decompression schedule if your computers
would lock up.
4. If you omit decompression, what you do depends upon how deep your stops were when
you had the omission, and how fast you can return to stop depth.
q True
q False
5. If you run out of gas, as a Tec 40 diver your options may include (choose all that apply)
q a. switching back to back gas.
q b. sharing with a team mate or support diver.
q c. decompressing for as long as possible with what you have to minimize DCS risk.

How did you do?

1. True. 2. c. 3. a, d. 4. True. 5. a, b, c.

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40 Knowledge
Reviews
Tec Deep Diver
Digital Manual

Instructor Guide

Tec 40 Knowledge Review One

Please complete this review to hand in to your instructor. If there’s something you
don’t understand, review the related material. If you still don’t understand, be sure to have
your instructor explain it to you.

1. Define “recreational diving”, “technical diving”, and explain what is not technical diving.

2. List six general risks and hazards that technical diving presents that either don’t
exist or aren’t as severe in recreational diving.

3. What single statement sums up the difference between recreational and technical diving?

4. What are the goals of the Tec 40 course?

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 5. What are the limits of the Tec 40 certification?

6. What are the six characteristics of a responsible technical diver:

7. What should you do if you can’t or won’t accept the risks and responsibilities
demanded by technical diving?

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8. Describe the proper types, number, location and configuration within your rig of
the following equipment components as to how your gear will look when worn.
Valves & Cylinders:

Right Regulator accessories:

Left Regulator accessories:

BCD and harness:

Instruments:

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 Instructor Guide Appendix

Cutting tools:

Pockets:

Clips:

9. List the three types of dive computer you can use for technical deep diving with air
and enriched air, along with the advantages and disadvantages of each.
Standard Air Computer:

Enriched Air Computers:

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Multigas Computers:

10. What are the recommended maximum oxygen partial pressures for technical
deep diving?

11. Using the maximum depth formulas, what are the maximum depths and decom-
pression depths for EANx48?

(Metric) if your SAC rate is 24 litres/min, how much gas volume do you need for 20
minutes at 30 metres? What would your total volume be with a reserve based on the
rule of thirds?

(Imperial) if you SAC rate is .8 cubic feet/min, how much gas volume do you need for
20 minutes at 90 feet? What would your total volume be with a reserve based on the
rule of thirds?

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12. What are the signs and symptoms of CNS oxygen toxicity, and what’s the primary
way you avoid it?

13. What are the signs and symptoms of pulmonary oxygen toxicity, and what is the
primary way to avoid it?

14. List your responsibilities as a team member when technical diving.

15. What is the rule regarding aborting a technical dive?

16. What is the primary hazard of diving negatively buoyant, and how do you manage
this hazard?

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 Appendix Instructor Guide

17. What is the primary hazard of excessive positive buoyancy, and how do you man-
age this hazard?

18. Describe how to find the minimum weight and the minimum buoyancy you need
for a technical deep dive.

19. How does a technical dive in a dry suit differ from a recreational dive in a dry suit?
What’s the recommended number of recreational dives in a dry suit that you
should have before technical diving in one?

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 Instructor Guide Appendix

20. Describe the procedure for sharing gas with your long hose.

21. What are the emergency procedures for a massive regulator (second stage) free
flow at depth?

22. What are the emergency procedures for a damaged doubles manifold at depth?

23. What is the over-riding mission of all technical dives?

24. How and why does “cutting corners” lead to accidents in technical diving?

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 Instructor Guide Appendix

Tec 40 Knowledge Development Two

Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 64-64, Thinking Like a Technical
Diver I, Tec Exercise 1.7
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 88-93 Introduction to
Decompression Stop and Gas Switch, Extended No Stop Diving, Equivalent
Air Depths (Continued) and Equivalent Narcotic Depths, Ideal Enriched Air
for a Particular Depth, Determining Gas Supply and Reserve Requirements for
Multiple Depths and Decompression stops (first page only); pgs 97-99 Desk Top
Decompression Software Tec Exercise 2.2, Questions 1-8 & 10. Pg 157 down to
“Example” on pg 158, Planning a Decompression Dive Using a Single Gas Computer.
Other Delivery Content, Tec 40-4
Study assignment: Tec 40 Handout 4
Other Delivery Content, Tec 40-5
Study assignment: Tec 40 Handout 5
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 101-107, Thinking Like a
Technical Diver II, Team Diving II, Tec Exercise 2.3, pgs 109-113, Predive Check,
Technical Diving Hand Signals, Tec Exercise 2.4, questions 1-3 and 9-15.
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 167, When to Make Cylinder
Switches, pgs 162-166, Emergencies III, Tec Exercise 3.3

Tec 40 Knowledge Review Two

Please complete this review to hand in to your instructor. If there’s something you
don’t understand, review the related material. If you still don’t understand, be sure to have
your instructor explain it to you.

1. Describe a suitable, rigged stage deco bottle “package.”

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 Appendix Instructor Guide

2. Briefly list the guidelines regarding material and equipment compatibility using
enriched air and oxygen. What do you risk if you fail to follow these guidelines?

3. Explain how you determine your required decompression stops using a single gas
computer or table, and how to use switches to enriched air or oxygen to make the
decompression more conservative.

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 Instructor Guide Appendix

4. What do you assume your END is with enriched air? Why?

5. What are the advantages and risks of using desk top decompression software?

6. What should you assume about every technical dive, and what should you take
for granted?

7. What is your most important resource in a tec diving emergency, and what provides
this resource?

8. What is the principle of your gas reserve?

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 Appendix Instructor Guide

9. What is the recall phrase for the seven segments of planning a tec dive, and what
does the phrase stand for?

10. Why do all team members on a technical dive usually use the same gases?

11. What four markings should be on every cylinder used on a technical dive? Which
should be easy to read by all team members while worn? Why are these markings
required?

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 Instructor Guide Appendix

12. Who must check the pressure and oxygen analysis of every cylinder used for a
technical dive?

13. What is the predive check recall phrase in tec diving? What does it stand for, and
what steps does the predive check include? Being Wary Reduces All Failures.

14. What is your turn pressure if you have 190 bar or 2800 psi in your cylinders and
your are using a reserve of one-third?

15. Describe how to perform a bubble check and a descent check.

16. The thumbs up means_________________________ .

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 Appendix Instructor Guide

17. What is the ideal position and stop depth level when decompressing? What is the
most important skill you need for decompressing?

Student Diver statement: I’ve reviewed the questions I answered incorrectly or incompletely
and I now understand what I missed.

Signature _________________________________________ Date ________________

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 Instructor Guide Appendix

Tec 40 Knowledge Development Three

Other Delivery Content, Tec 40-6
Study assignment: Tec 40 Handout 6
Other Delivery Content, Tec 40-7
Study assignment: Tec 40 Handout 7
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pg 204, sidebar, How Do I Figure 1.5
Times with a Computer?

Tec 40 Knowledge Review Three

Please complete this review to hand in to your instructor. If there’s something you
don’t understand, review the related material. If you still don’t understand, be sure to have
your instructor explain it to you.

1. What is one of the most common preventable causes of death in technical diving?

2. What is the recall acronym for gas switches? Describe the gas switch procedure and
how the acronym prompts you.

3. List five guidelines that reduce the chance of accidentally switching to an unsafe gas
blend at depth.

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 4. Describe what to do if you experience possible symptoms of CNS oxygen toxicity.

5. What is the “ideal” gas blend for a dive to 25 metres/83 feet?

6. What is the general procedure if you can’t return to your planned ascent line?

7. How do you learn to account for environmental variables, such as current, visibility,
temperature and waves when planning a tec dive?

8. What are four guidelines to consider when planning a tec dive in an unfamiliar
environment?

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 Instructor Guide Appendix

9. What assumption do technical divers make when they plan a dive?

10. List six principles for surviving a tec dive.

11. As a Tec 40 diver, what should you do if you exceed your planned depth and time?

12. As a Tec 40 diver, what should you do if you omit decompression?

Student Diver statement: I’ve reviewed the questions I answered incorrectly or incompletely
and I now understand what I missed.

Signature _________________________________________ Date ________________

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 Tec Deep Diver
Digital Manual

45

Independent
Study
Assignments

Chapter 4

Chapter 5

Handouts

Knowledge
Reviews

Appendix

Main Menu

Tec 45 » Chapters Four and Five

 Instructor Guide 45 Tec Deep Diver
Digital Manual
Independent
Appendix
Study Assignments
Tec 45
Tec 45 Knowledge Development One
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 10-33, Equipment I, Tec Exercise
1.2, pgs 80-87, Equipment II, Tec Exercise 2.1, pgs 142-145, Equipment III, Tec
Exercise 3.1
Watch the TecRec Equipment Setup and Key Skills video.
Other Delivery Content, Tec 45-1
Study assignment: Tec 45 Handout 1
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 93-97, Determining Gas Supply
and Reserve Requirements for Multiple Depths and Decompression Stops
pgs 146 -161, Gas Planning III, Tec Exercise 3.2
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 167-172, Turn Around Points and
Environmental Variables, Tec Exercise 3.4, questions 2-4
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 173-175, Team Diving III, Tec
Exercise 3.5

Tec 45 Knowledge Review One

Please complete this review to hand in to your instructor. If there’s something you
don’t understand, review the related material. If you still don’t understand, be sure to have
your instructor explain it to you.

1. What are the limits of your training as a Tec 45 diver?

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 Knowing ignorance is strength.
Ignoring knowledge is sickness.

— Lao Tsu, Chinese philospher,

6th Century BC, Tao Te Ching,
Feng-English translation

T
hree behind you and here you are: Chapter
Four. By now you should understand the foun-

FOUR
dational principles behind tec diving well, have
a good picture of how they fit together with the
techniques and skills tec diving requires, and
be growing comfortable with your ability to demonstrate
and apply those techniques and skills. As you continue
to practice and develop your abilities, Chapter Four starts
focusing you on some of
Chapter FOUR: The Details the finer points that you
need to tec dive success-
fully. Until you had the big picture behind you, you’d have
trouble grasping some of these, or understanding how they
fit amid the foundation, framework and structure of what
you’ve learned already.
Chapter Four starts out by looking at still more tec diving
equipment, but with an interesting spin — homemade gear.
You might find it interesting to learn that there’s some
stuff you’re expected to make yourself. From there you’ll
get back into gas planning, which by now you realize forms
the very heart of deep tec diving. In this chapter, you’ll
turn your focus away from decompression diving for a bit,
and look at the other option open to tec divers, the gas-
switch, extended no-stop dive.

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 Next comes some more about emergencies (yep,
there’s more), and then back to the philosophy
lessons and thinking like a tec diver. If you’re com-
pleting only the Apprentice Tec Diver at this
point, there’ll be some advice just for you, and
that’ll be it for Chapter Four.
At this point, each chapter will become notice-
ably shorter, but you’ll find each Practical
Application and Training Dive becoming a bit
more demanding as your instructor leaves you
and your team to do more and more indepen-
dently. That’s as it should be — you had to learn
a lot of theory and principles to get going, but as
you get that behind you, you’re zeroing in more
and more on applying what you’ve learned.
At this point, each chapter will become notice-
ably shorter, but you’ll find each Practical
Application and Training Dive becoming a bit
more demanding as your instructor leaves you
and your team to do more and more indepen-
dently.

Equipment IV
Tec Objectives
Homemade Gear? Because tec diving is evolving rap-
Highlight or underline the idly and taking on new challenges, it’s not unusual
answers to these questions for tec divers to have to create special equipment for
as you find them: special purposes, or adapt something for an underwa-
1. Why would technical divers ter need. In other words, you might use homemade
use “homemade” equip- gear because you have no choice — a commercial
ment? version doesn’t exist. This really isn’t anything new;
2. What are examples of since diving’s early days many new concepts and
acceptable and unaccept- innovations have originated with improvised inven-
able instances in which tions.
a tec diver might use
“homemade” gear? But of course, you can take things too far. Unless you
3. What are six general guide- happen to be talented with metal machining and in
lines regarding the use of gas fluid dynamics, you probably shouldn’t be using
“homemade” equipment? a homemade regulator! It’s considered acceptable to
4. What is probably the most use homemade stuff for equipment that is not criti-
common “homemade” cal for safety and/or life support, and for which there
item used by tec divers? exists no professionally made version.

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 More than you might imagine falls into this category. Examples
include specialized compass slates for mapping, bungees-clip
arrangements for securing accessories,
binder rings for attaching laminated deco
tables to slates, and so on. Some accessories
designed and appropriate for recreational
diving may approximate, but not really
meet tec diving’s requirements. And, what
you have to make at this writing may well
be commercially available by the time you
read this — progress marches on.
Unacceptable examples might (obviously)
include a BCD or regulator, line reel, lift
A bungee or surgical tubing “necklace” to hold
your short hose second stage is an example of bag, etc. These are readily available from
appropriate homemade gear. professional sources, and they’re life sup-
port or key safety equipment. An individual
who’s highly skilled and trained at working
with materials might make a suitable version of some of these, but
the appropriate degree of skill required would be such that you
might consider this a one-of-a-kind professional item anyway.
The following six guidelines apply to “home-
made” items:

FOUR
1. Be sure you really need it. Keep things
simple.
2. Confirm that a professionally made version
does not exist.
3. It should provide a clear benefit or meet an
important need, yet not create a hazard nor
be essential to safety and life support.
4. Try the item during some no stop, simple
dives before using it on a demanding tec dive.
5. Get an opinion from one or more experienced
tec divers who you respect.
6. When in doubt, do without it.
Another example of homemade gear is a
The most common “homemade” item is one custom dive table generated by desk top
you’ll make yourself — in fact, you may have deco software and then laminated or print-
already as part of this course: a custom dive ed on waterproof paper for use or backing
up a computer during the dive.
table generated by desk top deco software and
then laminated or printed on waterproof paper
for use during the dive. (The numbers aren’t “homemade” of
course, but the printing and laminating are.)
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 Tec Exercise – 4.1

1. You might use homemade equipment because: 3. Unacceptable examples of homemade gear include
a. the equipment you need doesn’t exist. (check all that apply):
a. binder rings for slates and tables.
b. the guy at the dive store said you can make a bet-
ter lift bag yourself. b. regulators.
c. it’s the best way to get dependable life support c. bungees-clip arrangements.
equipment. d. BCDs.
d. None of the above.
4. Guidelines regarding the use of homemade equipment
2. Acceptable examples of homemade gear include (check include (check all that apply):
all that apply): a. Be sure you really need it.
a. binder rings for slates and tables. b. Try it on simple dives first.
b. regulators. c. Get an opinion from experienced tec divers you
c. bungees-clip arrangements. respect.
d. BCDs. d. If in doubt, try it out.

5. The most common “homemade” equipment is a lami-

nated custom _________ _________.

Check it out.
1. a. 2. a, c. 3. b,d. 4. a,b,c. d is wrong — if in doubt, do without. 5. dive table.

Gas Planning IV
Gas-switch, Extended No Stop Dives
Technical deep diving tends to focus on decompression diving
because typically, the depths and times required call for stage
decompression. However, when you’re trained to handle stage/deco
cylinders and make gas switches, you can also make gas-switch,
extended no stop dives. As you recall, a gas-switch, extended no
stop dive is a dive in which you gain bottom time by ascending to a
shallower level and switching to a richer EANx. This gives a longer
no stop time through both the multilevel profile and the gas switch.
It’s no stop diving, but considered tec diving because of the equip-
ment involved, and because you may be carrying gas blends deeper
than you can safely breathe them.

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 In the last chapter you saw that the no stop
Tec Objectives increase is substantial, usually with so much
time that even using multiple cylinders, you can
Highlight or underline the stay well within no stop limits. Especially when
answers to these questions diving shallower than 40 metres/130 feet for
as you find them:
the first level, gas-switch extended no stop dives
1. What are the procedures work well with single cylinders for back gas. It
for staging and switching is possible, though not common, to make gas-
gases when making gas-
switch, extended no stop dives with more than
switch, extended no-stop
dives? two blends.

2. What do you do if you Gas-switch, Extended No Stop Procedure. Gas-

cannot switch to your switch, extended no stop dives require desk top
shallower gas blend, or if deco software, and/or a multigas computer. You
you must switch back to begin by choosing your back gas based on the
the deeper blend when
making a gas-switch,
bottom depth, and your second blend based on
extended no-stop dive? your planned second depth level, making sure
you don’t exceed the 1.4 ata maximum depth
3. How do you plan and
make a gas-switch,
for the blend.
extended no-stop dive You start the dive at the deepest point, and then
using desk top decom-
at a certain point (usually based on your dive
pression software?
time and/or back gas pressure), you ascend to
4. How do you plan and your second level and NO TOX switch to your

FOUR
make a gas-switch,
stage cylinder with the richer blend. You use the
extended no-stop dive
using a multigas dive stage cylinder and stay at or above the second
computer? level depth for the rest of the dive.
5. How can you make a gas- As you recall, it’s best to stage a cylinder rather
switch, extended no-stop than carry it deeper than you can breathe it
dive more conservative? safely, and that’s quite often possible when
6. How do you make a making gas-switch, extended no stop dives.
safety stop while within a But, you may need to carry it the whole time,
decompression stop? depending on the site and logistics.
7. What is “runtime,” how
do you determine it, and
Plan an appropriate reserve in both cylinders,
how do you use it? but since you’re staying in no stop limits, a
35-70 bar/500-1000 psi reserve is usually ade-
8. What do you do if you
find yourself slightly
quate. If, for some reason you can’t make your
ahead of your runtime? gas switch (such as you staged the cylinder and
can’t retrieve it), you end your dive following
9. What is “gas matching”?
the no stop limits/oxygen limits, etc. for your
back gas.
If, for some reason, you have a problem with your shallow blend,
you obviously have to switch to your back (deeper) gas. If you’re
not using a multigas computer, it may be simplest to finish the dive

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 as though you made all of it on your back gas. If you’ve already
passed the no stop limits for your back gas when you switch back to
it, and if you’ve been staying within no stop limits (as you should
have been), ascend immediately and make a three minute or longer
safety stop at 5 metres/15 feet.
Planning Gas-Switch, Extended No Stop Dives Using Desk Top
Deco Software. Writing a table for a gas-switch, extended no stop
dive is pretty straightforward with most desk top decompression
programs. Open a new dive profile and enter your
first depth, EANx and desired time within no stop
limits. Enter your second level, second EANx and
find your no stop limit (you may be limited by
oxygen instead of no stop time). Some programs
won’t automatically find no stop limits, so to find
them you increase your bottom time until the
program says you need decompression, and then
back off.
When in doubt, assume and plan for a deeper sec-
ond level as opposed to a shallower one. You can
always stay shallower than the planned second
level without affecting your dive plan.
Once you have your dive plan down, most pro-
Even if you have a multigas computer, you’ll
probably find you want desk top deco soft-
grams will generate tables based on variations of
ware for planning gas-switch, extended no
stop dives. your depth and time. Take this with you so you’ve
got flexibility and back up schedules when you
execute your dive. It’s also wise to carry tables and/or a dive com-
puter based on making the dive entirely on your back gas (in case,
for some reason, you can’t switch to the shallow mix). Keep in mind
that a single gas computer may lock up due to omitted deco after a
long second level, however, since it won’t know you switched gases.

Planning Gas-Switch, Extended No Stop Dives Using Multigas

Dive Computers. Using a multigas dive computer gives you maxi-
mum versatility with gas-switch, extended no stop dives. Choose
the blends for the depth levels and enter them into the computer
per manufacturer instructions.
Start with your deepest depth and blend. You switch gases on the
computer after you ascend to the next level and NO TOX switch to
the richer EANx. If you must switch back to back gas for some rea-
son, you switch your computer and it automatically gives your new
no stop times. Using a computer gives you more versatility in terms
of depths, or needing to switch back and forth.

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 Although the multigas computer calculates automatically, you’ll
still want to use desk top deco software to assist with dive planning.
Again, it’s a good idea to carry a back up computer or tables. If
these are single gas, they should be set or based on the lowest oxy-
gen EANx (back gas).
Making Gas-Switch, Extended No Stop Dives More Conservative.
Since you’re using an increased fraction of oxygen to extend your
bottom time instead of to pad your schedule, you need to use other
techniques to make gas-switch extended no stop dives more con-
servative. The easiest way is the one you already know - stay well
within no stop limits; ascend and switch well before reaching the
deeper level limits.
You can also plan your dive based on EANx blends with somewhat
less oxygen than you actually use. For example, you could plug
in EANx30 and EANx40 in your desk top/multigas dive computer,
but dive with EANx32 and EANx45 (making sure not to exceed
the maximum depth for these blends). If you do this, you’ll need
to track oxygen exposure manually because the computer doesn’t
know what you’re really breathing. You’ll also need to calculate
and plan oxygen exposure manually for repetitive dives.
With some multigas computers, if not inconsistant with the manu-

FOUR
facturer’s instructions, you can set the actual blends you’re using,
but set the computer for a higher altitude than actual. This renders
more conservative no stop limits while tracking oxygen exposure
accurately.

Safety Stops Within

Decompression Stops
As a recreational diver, you learned to
make safety stops — a stop at 5 metres/15
feet for three to five minutes not required
by your tables or computer for added
conservatism. You can do the same thing
as a tec diver on a decompression dive by
over staying your last deco stop by five
minutes. For example, if your table says
you require nine minutes at 3 metres/10
feet, you stay 14. Or, if your computer
clears you to surface, and you stay anoth- After surfacing from a particularly strenuous dive or long
er five minutes. Doing this with oxygen, deco dive, “safety stop” at the surface by resting in the
in particular, adds a good measure of water for another five to 15 minutes before exit.
conservatism.

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 After surfacing from a particularly strenuous dive or long deco dive,
“safety stop” at the surface by resting in the water for another five
to 15 minutes before exit. You may continue to breathe EANx or
oxygen. Remember that even though you’re at the surface, if you’re
breathing EANx50 or higher, the CNS clock is running and you’re
gathering OTUs; be sure to calculate these in your oxygen exposure.

Runtime
When following tables through a dive and decompression, the
traditional method is to arrive at a stop, time it for the required
minutes, go to the next stop, time it, and so on. Runtime is an easier
way to handle your dive schedule. Runtime is a continuous elapsed
schedule you follow from the beginning to the end of the dive when
following a table. It accounts for your descent, ascent, and decom-
pression time, and it tells you where you should be against elapsed
time. Rather than time each depth and phase separately, you fol-
low a continuous time. To use runtime, you simply depart from the
depth when you reach the elapsed time listed for that depth, and
head for the next depth at the predetermined ascent rate.
You create runtime by adding the times for each dive phase and
deco stop in sequence, including ascent time (round minutes to
closest whole minute, up or down). Usually, you include descent
time in your bottom time.
By now you might be sick of hearing how desk top deco software
makes life easier by all the things it does for you, and here’s anoth-
er one. Desk top deco software will generate runtime automatically,
sometimes with less rounding. The programs sometimes repeat a
depth to show arrival and departure times, but the concept’s the
same. When generating multiple tables, some programs will gener-
ate runtimes for alternative schedules as well as for your planned
one. That way, you can use runtime in a contingency situation.
Here’s an example of calculating runtime by hand: You’re making
a 30 minute dive to 30 m/100 ft using air and your table calls for a
stop for one minute at 6 m/20 ft and 15 minutes at 3 m/10 ft. Your
runtime would be:

Depth Time Runtime How derived

0 m/0 ft 0 0

30 m/100ft 30 30 (0 + 30)

6 m/20 ft 1 34 (30 + 3 min ascent + 1 min stop)

3 m/10 ft 15 49 (34 + 15 — ascent less than .5 minute ignored)

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 Runtime is simple to follow, but if you find yourself slightly ahead
of runtime, (you leave the bottom a bit early for example), adjust
to merge gradually with the runtime. For instance, using the previ-
ous runtime example, suppose you leave the bottom at 29 minutes
instead of at 30. You merge by ascending slightly slower than usual
so that you reach 6 m/20 ft in 3.5 minutes, and then stay 1.5 min-
utes at the stop to reach the 34 minute mark. Now you’re on the
runtime; ascend to 3 metres/10 feet and stay until runtime reach 49
(plus a safety stop if you want). If you get behind your runtime, you
usually need to switch to the next longer decompression schedule.
Air breaks and gas switches when you return to back gas don’t count
as decompression time. You can handle this several ways. One is by
using a dive watch with a stopwatch function and stopping the run-
time during air breaks/gas switches. If you’re calculating your run-
time manually, the easiest thing to do is to add them into your run-
time. Some desk top deco software will automatically add air breaks,
but others won’t and you have to put them in yourself.
Runtimes work well with gas-switch, extended no stop dives. Your
runtime shows the point by which you must ascend from each deep-
er level to the next shallower level. If you go up ahead of the time
indicated, no problem. The dive becomes more conservative than
planned, so you can still follow the runtime without adjustments.

FOUR
Gas Matching
In tec diving you’ll hear a fair bit about gas matching, particularly
in diving that involves overhead environments (caves and wrecks).
Gas matching is a technique that accounts for teams with members
who have different breathing rates and cylinder sizes. It helps assure
that should the diver with the highest SAC rate and gas supply have
complete gas loss at the furthest penetration point, a team mate
with a lower gas supply volume and lower SAC rate have sufficient
gas reserve for both divers to exit. The idea is for the diver with the
smaller gas volume/lower SAC rate to reserve a volume equal to
one-third of the larger gas supply.
Because you can usually ascend immediately or very soon in deep
open water tec diving, gas matching isn’t typically used in open
water tec diving. However, if you become qualified to make wreck
penetrations or cave/cavern dives, gas matching is very important.
For open water tec diving it’s sufficient to determine your actual
gas volume before each dive to be sure you have enough gas, plus
reserve, to make the dive as planned. However, you may find it
handy in situations in which you want to return to a particular

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 point before ascending, such as along an anchor line when there’s
a moderate surface current. In this case, you might plan to come
back before ascending, and gas matching provides the option of
doing so if assisting a team mate with more gas and a higher SAC.
(Obviously, you still should have your lift bag, deco cylinders and
be prepared to ascend directly).
When gas matching, the diver with the larger volume and SAC rate
plans to turn the dive upon reaching thirds (after using one third of
the gas supply). Then, you use what you’ve already learned about
determining tank base lines to match:
In metric:
1. Take the volume of the larger gas supply and divide by three.
This is the amount that must be reserved by the diver with the
smaller supply.
2. Divide the reserve by the capacity of the smaller gas supply
cylinders. The result is the reserve pressure that the diver with
the smaller gas supply should have left at the end of the dive if
there’s no emergency.
3. Subtract the reserve pressure from the actual pressure of the
smaller cylinders, divide that by two, and subtract the result from
the actual pressure to get the pressure turn around point for the
smaller gas supply.
Example: You’re diving with twin 11 litre cylinders with 200 bar.
Your team mate has twin 21 litre cylinders with 160 bar. What
should your reserve pressure be, and what’s your one-third turn
around pressure?
Answer: 102 bar reserve pressure; 151 bar turn around
Team mate’s volume = 21 x 2 x 160 = 6720 litres
Reserve = 6720 ÷ 3 = 2240 litres.
reserve divided by your tank capacity = 2240 ÷ 22* =
102 bar reserve you should have left
200-102 = 98 bar you can use; 98 ÷ 2 = 49; 200 - 49 = 151
*22 because double 11 litre cylinders

In imperial:
1. Take the volume of the larger gas supply and divide by three.
This is the amount that must be reserved by the diver with the
smaller supply.
2. Divide the reserve volume by the base line of the smaller cylin-
ders. The result is the reserve pressure the diver with the smaller
gas supply must maintain.

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 3. Subtract the reserve pressure from the actual pressure of the
smaller cylinders, divide that by two and subtract it from the
actual pressure of the smaller cylinders to get the turn around
point for the smaller gas supply.
Example: You’re diving with twin 80 cubic foot cylinders, working
pressure 3000 psi, with 2950 psi in them. Your team mate has twin
120 cubic foot cylinders, working pressure 2400 psi, with 2350 psi
in them. What should your reserve pressure be, and what’s your
one-third turn around pressure?
Answer: 1473 psi reserve pressure; 2213 turn pressure
Team mate’s baseline = .1 (240 ÷ 2400 = .1) ; Team mate’s volume
= 235 cf (2350 x .1); Team mate’s reserve = 235 ÷ 3 = 78.3.
Your baseline = .053 (160/3000 = .053).
78.3 ÷ .053=1477; 2950 - 1477 = 1473, 1473 ÷ 2 = 736.5;
2950-737=2213

Depending upon logistics and the environment you’re in, your

instructor may have you gas match on your dives. Keep in mind
that even if you don’t need to gas match, you always need to
determine actual gas supplies, reserves and turn points as you’ve
learned already.

FOUR
Tec Exercise – 4.2

1. When making gas-switch, extended no-stop dives 3. When using desk top deco software to plan a gas-
(check all that apply): switch, extended no-stop dive, if in doubt about the
a. choose your second blend based on your sec- second level’s depth, plan a ___________ level as
ond depth level. opposed to a ________ one.
b. after ascending to the second level and switch-
ing, you stay on the second blend for the rest of 4. Although the multigas computer calculates gas-
the dive. switch, extended no-stop dives automatically, you’ll
c. it’s crucial to observe the rule of thirds, or a still want to use ____ ____ _____ ______ to assist with
more conservative reserve. dive planning.
d. None of the above. 5. To make a gas-switch, extended no-stop dive more
conservative (check all that apply):
2. If you cannot switch to your shallower gas blend, or
a. dive with gases that have less oxygen than
if you must switch back to the deeper blend when
those you planned the dive with.
making a gas-switch, extended no-stop dive (check
all that apply): b. set a multigas computer for a lower altitude
a. switch your multigas computer accordingly, if than actual.
you’re using one. c. get as close as possible to the no stop limits.
b. assume the whole dive was made on back gas d. None of the above.
if using tables.
c. stay within no stop limits.
d. None of the above.

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 Tec Exercise – 4.2 continued

6. To make a safety stop within a decompression stop, 8. If you find yourself slightly ahead of runtime, you’ll
you over stay your required time on the last stop by have to abandon the runtime and use the deco
five minutes (or more). schedule for the next deeper depth and longer time.
True False True False

7. To use runtime, you simply _____ from the depth 9. Gas matching is a technique that accounts for teams
with members who have different breathing rates
when you reach the elapsed time listed for that
and cylinder sizes.
depth.
True False

Check it out:
1. a,b. c isn’t correct because you’re making a no stop dive and a less conservative reserve is usually acceptable. 2. a,b,c. 3.
deeper, shallower. 4. desk top deco software. 5. d. 6. True. 7. depart. 8. False. If you’re slightly ahead of runtime, adjust to
gradually merge with it. 9. True.

Emergencies IV
In the last chapter you learned to handle possible emergencies,
most of which could happen but are usually easy to prevent. Most
of the emergencies in this chapter fall into the same category. If
you emphasize good diving technique and adequate planning, you
should never face most of these — but you should still know what
to do, just in case.

TEC Objectives

Highlight or underline the answers to these questions as you find them:

1. How do you ensure that you don’t lose your 5. What should you do if you have a delay in your
deco cylinders, and what should you do if you ascent to a decompression stop?
do?
6. What should you do if you omit some or all of
2. What do you do if your dive goes deeper and/or your decompression?
longer than your planned dive?
7. What should you do if you run out of gas?
3. How can you use a single gas dive computer to
8. What is a “drift kit,” when you would you use it
back up a multigas computer?
and what items would you have in it?
4. What should you do if you miss a decompression
9. How do you handle a lift bag that spills as it
stop?
ascends but cannot be pulled back down to
redeploy?

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 Lost Decompression Cylinders
Losing your deco cylinders can leave you without a complete solu-
tion, so this is definitely a problem with the emphasis on preven-
tion. Never stage your cylinders if you have any question whether
you’ll be able to return to them and retrieve them. Be cautious at
popular dive sites so you don’t stage cylinders where other divers
might take the “lost” tanks they “found.” When you leave them,
be sure they’re where they won’t roll, float or get swept away. Clip
them to something or otherwise secure them if possible. As you
learned, confirm that the valve’s closed, but the regulator pressur-
ized, on the staged cylinder before you leave — an empty cylinder’s
no more useful than a lost one.
If you do lose your cylinders, how difficult your situation is depends
on how much decompression you have and whether it’s based on
accelerated decompression or not. The primary issue will be wheth-
er you have enough gas volume to decompress adequately.
If you’re following a single gas table or computer and using deco
cylinders with higher oxygen for conservatism, then you can decom-
press on back gas. Provided you have enough volume, you give up
the conservatism but you should still decompress adequately.
If you’re making an accelerated decompression, you can carry

FOUR
single gas back up tables (desk top deco software), or (multigas
computers) keep the computer set for your back gas. The problem
here is that accelerated deco dives tend to be long dives with lots of
decompression in the first place, so you may not have enough gas
to complete your decompression.
With support divers, things may be easier. They may be able to
bring down standby cylinders, or to locate your missing cylinders.
When making accelerated deco dives, if using a multigas computer
and your team mates have not lost their deco gases, they can give
you what’s left of theirs as they finish. They’ll finish before you, but
you should be able to complete your decompression.
If you don’t have enough gas in your doubles to complete your
decompression, decompress as long as you can. When you surface,
breathe emergency oxygen and contact emergency medical care if
you suspect DCI (either DCS or AGE) symptoms.

Exceeding Your Planned Depth/Time

Good buoyancy control and control in the water should make this
a rare situation, and should it happen, it shouldn’t be an “emer-

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 gency” so much as a “situation.” You should prepare for this as a
regular part of dive planning (as you’ve already been practicing).
For tables-based dives, desk top deco software will generate a table
series based on times and depths less than and greater than your
planned time and depth for contingency purposes. Dive computers
will automatically calculate based on your actual dive profile. The
rule of thirds will generally accommodate the next longer/deeper
schedule, but you should compare the gas requirements to be sure.
Be prepared to alter time to accommodate depth. If you find your-
self deeper than planned, turn the dive sooner. Precision diving is
the key — you must master buoyancy control and closely monitor
depth, time and gas supply. Dive well and this won’t be an issue.

Backing Up A Multigas Computer with a Single Gas

Computer (Continued)
As you learned, you back up a multigas computer with a single
gas computer by setting the single gas computer for your back gas.
Decompress as if using back gas, with the higher oxygen blends for
conservatism. That’s pretty straightforward.

How Do I Figure 1.5 Times With a Computer?

S
upposed you’re following a computer based total deco time remaining), you determine by
decompression and have to follow the pro- noting the beginning and ending elapsed bottom
cedure for extending the 6 metre/20 foot time.
and final stops by 1.5 because you had to assist
After you complete that, ascend to the final stop
a team mate and went above your stop depth
for 1.5 times the remaining deco time you noted
for two minutes. The problem is that when you
on your slate.
overstay the 6 metre/20 foot stop, the computer
shortens what it predicts for your final stop (5 Example: You’re following the procedure and
metres/15 feet or 3 metres/10 feet) — but, you your elapsed bottom time is 56 minutes when
need to stay for 1.5 times the original time. you reach 6 metres/20 feet. At 66 minutes, the
computer clears you to the final stop and shows
Do this: Stay at your 6 metre/20 foot stop
24 minutes of decompression remaining. You stay
until the computer clears you to the last stop.
at 6 metres/20 feet for an additional five minutes
Immediately note the decompression time
(1.5 x 10 minutes). Then ascend to the final stop
remaining on your slate, and the elapsed bot-
for 36 minutes (1.5 x 24 minutes).
tom time, but do not ascend. Instead, stay at 6
metres/20 feet until you complete the 1.5 times Note: Some computers automatically calculate
the 6 metre/20 foot stop time, which either the missed deco stop procedures. See the manufac-
computer tells you, or if not (some only show turer’s instructions.

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 However, circumstances might require accelerated decompression.
This could be due to water temperature or because you can’t decom-
press on the back gas schedule because you don’t have the gas vol-
ume require. In this case, you need to carry accelerated deco tables
(generated by desk top deco software) and use the single gas com-
puter (or a depth gauge/timer) for time and depth information only.

Missed Decompression Stop

This emergency usually results from another emergency, such as a
gas shortage forcing you to skip a stop and ascend shallow enough
to switch to your next, richer
oxygen blend. If you’re div-
ing with care and precision, it
shouldn’t happen by accident
by itself.
If you miss a decompres-
sion stop, how you handle it
depends on the situation. If
you can, immediately (within
one minute) redescend and
complete the stop, plus one

FOUR
minute, and then decompress
according to the normal sched- If you miss a decompression stop, how you handle it depends on the
situation. If you can, immediately (within one minute) redescend and
ule. This might be an instance complete the stop, plus one minute, and then decompress accord-
in which, for example, you ing to the normal schedule. This might be an instance in which, for
assist an overly buoyant diver example, you assist an overly buoyant diver arrest an ascent.
stop an ascent.
If you cannot redescend (such as with the gas supply problem), stay
at the next stop for the combined time of both stops. Extend your
6 metre/20 foot stop and your final stop by 1.5 times the normally
scheduled decompression. If you’re using a dive computer, it may
lock up if you skip a stop and cannot redescend to complete it. You
may need to decompress according to back up tables.

Delay in Ascent to Decompression Stop

Variations in ascent aren’t unusual, but you shouldn’t typically
have a substantial delay. The simplest action is that if you’re
delayed ascending to your first decompression stop, add the delay
to your bottom time and decompress according to the new sched-
ule. Between stops delays aren’t usually as critical unless they’re
excessive (more than two or three minutes). Do not count the delay
as decompression time when you resume decompression.

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 When diving with a computer, the computer calculates in delays
automatically, extending decompression if necessary, so you need
only continue to follow the computer’s deco schedule. When you’ve
had a delay in ascent, it’s always wise to extend your last stop as
much as practicable.

Omitted Decompression
As with missing a stop, omitted decompression should only hap-
pen when another emergency causes it to happen. Divers who omit
stops because they can’t maintain a stop depth or because they
can’t follow a schedule need more experience and training before
they take up tec diving. The seriousness of omitted
decompression depends on the situation. It can be
minor to life-threatening.
Omitting all required decompression has high DCS
risk, especially if it’s greater than five or ten minutes.
The more decompression you’ve completed, the less
risk (obviously). If decompressing with a single gas
computer/table and using EANx/oxygen for conser-
vatism, your risk is relatively low if you’ve completed
most of your decompression.
If you omit decompression from 6 metres/20 feet or
shallower, if you have no DCS symptions and it’s pos-
sible, return to depth within one minute and complete
your decompression as scheduled. As a precaution,
If you omit decompression from 6 extend your last stop several minutes or more.
metres/20 feet or shallower, and you
have no DCS symptoms but it takes lon- If you omit decompression from 6 metres/20 feet or
ger than one minute to return to your shallower, and you have no DCS symptoms but it
stop depth, extend your 6 metre/20 takes longer than one minute to return to your stop
foot stop and/or the final stop by 1.5
times the decompression normally depth, extend your 6 metre/20 foot stop and/or the
required (or longer on the final stop, as final stop by 1.5 times the decompression normally
possible). This might be the case if you required (or longer on the final stop, as possible).
have to surface for more deco gas due
to an emergency. If you omit decompression from deeper than 6
metres/20 feet, return to the first stop depth as quickly
as possible (ideally less than five minutes) and decom-
press according to schedule up to and including the 12 metre/40
foot stop. Extend the 9 metre/30 foot stop and all shallower stops
by 1.5 times their scheduled times.
If you cannot return to depth (no gas available, for instance),
breathe emergency oxygen, remain calm and monitor yourself for
DCS symptoms. If you surfaced owing more than a few minutes

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 decompression or skipped all your decompression, assume you will
get bent and have your team begin preparing for emergency evacu-
ation. Stay on 100 percent oxygen until reaching emergency medi-
cal care.

Running Out Of Gas

Running out of gas by breathing it down should not occur if you
plan your reserve appropriately and turn your dive at the right
point. Unexpected exertion or a sudden freeflow can cause you to
exhaust gas faster than expected, even with a quick valve shut-
down, but normally your reserve should cover these problems. You
should not run out of gas on the bottom because you should be
ascending to your first stop depth before that happens. However, it
is possible to have a gas shortage and perhaps run out following a
severe, difficult to control gas loss, such as a manifold failure when
you’re almost at your turn point.
Your first option is to see if your team mates or support divers can
help by sharing gas or bringing some down. If you exhaust a deco
gas using tables, ascend to the first stop where you can use your
next gas. Combine missed stops with the stop at that depth, unless
this will prematurely exhaust that gas, too. In that case, follow the

FOUR
decompression schedule and extend the shallower stops as much as
practicable.
If you exhaust a deco gas using a single gas computer or table,
simply complete decompression on back gas, (you have to have
enough volume to do so, of course). If you exhaust a deco gas using
a multigas computer, switch to
back gas and select that gas on
the computer. Decompress on the
new schedule the computer pro-
vides. The more decompression
you complete before you exhaust
the deco cylinder, the more likely
you’ll have sufficient back gas
volume to complete your decom-
pression.
As a general guideline, if gas
termination interferes with your
As a general guideline, if gas termination interferes with your decom-
decompression, decompress as
pression, decompress as long as you can as best you can with what
long as you can as best you can you have. Even if you end up getting DCS, the more decompression
with what you have. Stay down you completed, the less severe it should be.

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 with team mate’s high oxygen deco cylinders after they complete
decompression, if possible. Even if you end up getting DCS, the
more decompression you completed, the less severe it should be.

Drift Kits
A possible risk in open ocean diving, or even in some major lakes,
is ending up adrift in the current a considerable distance from the
boat. If diving where this could happen, you should carry a drift
kit, which is a kit with emergency items. The most elaborate are
watertight/pressure proof containers bracketed to the doubles; the
simplest are items in a pocket or pouch.
You use your drift kit if you surface and cannot see the dive boat,
or it is too far away to reach and you’re having trouble getting the
crew’s attention. At a minimum a drift kit contains an inflatable
signal tube (safety sausage) and a whistle. In higher risk current
environments, you may consider adding a signal mirror, watertight
flasher, and for the highest risk environments, a portable EPIRB
(Electronic Positions Indicating Radio Beacon — allows authorities
to find you electronically when activated) in a pressure proof cas-
ing. Flares, smoke flares and aircraft dye markers can also make
you easier to spot for pickup. In areas with cell service that extends
well out over the water, some divers carry mobile telephones in
small underwater housings so they can ring up help if they need to!

Partly Spilled Lift Bag

If you send up a lift bag without sufficient line tension, it can partly
spill at the surface, leaving it too buoyant to pull down and rede-
ploy, but insufficiently buoyant
for use as a firm decompression
line. Your first option is to send
up a team mate’s lift bag clipped
to the same line via a carabiner
or large bolt snap (small snaps
can hang up). Using the same
line combines their lift and avoids
entanglement from two lines in
water.
As a second option, your team
mate deploys a lift bag entirely If you can’t pull a partially spilled bag down, then there’s
separately. This means there are sufficient buoyancy to use the bag as is. You’ll need to
two lines to deal with, but it’s be careful with your buoyancy, but you should be able to
decompress along the line adequately.

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 an option if you have some doubt about what’s going on with the
line. Finally, if you can’t pull the bag down, then there’s sufficient
buoyancy to use the bag as is. You’ll need to be careful with your
buoyancy, but you should be able to decompress along the line
adequately.

Tec Exercise – 4.3

1. If you lose your deco cylinders (check all that apply): 6. To handle omitted decompression (check all that
a. how difficult your situation depends on how apply):
much deco you have. a. if no DCS symptoms, return to depth within five
minutes and complete your decompression, then
b. if using a single gas table/computer, decompress
extend your last stop as long as you can.
on back gas.
b. if you can’t return to depth, breathe emergency
c. your team mates may be able to give what’s left
oxygen and monitor yourself for DCS symptoms.
of their gases.
c. you don’t need to worry much if you omitted
d. if all else fails, decompress as long as you can
one hour or less decompression.
with whatever gas you have.
d. None of the above.
2. You should prepare for your dive going deeper and/
7. If you run out of gas underwater (check all that
or longer than planned as a regular part of _______
apply):
________.
a. see if your team mates or support divers can
share gas.

FOUR
3. If circumstances require accelerated decompression
when using a single gas computer to back up a multi- b. if possible, ascend to the first stop at which you
gas computer, you should carry ________ ____ ______ can switch to the next gas.
and use the single gas computer only for depth and c. finish using back gas, if possible and if using a
time information. single gas computer or table.
d. if all else fails, decompress as long as you can
4. If you miss a decompression stop (check all that
with whatever gas you have.
apply):
a. if possible, immediately redescend and complete 8. Items you might carry in a drift kit include (check all
your stop. that apply):
b. stay at the next stop for the combined time of a. inflatable signal tube c. EPIRB
both stops. b. signal mirror d. whistle
c. extend your final stop by ten minutes or more.
9. If your lift bag partially spills but you can’t retrieve and
d. None of the above. redeploy it, your first option is
a. to have your team mate send up a separate bag
5. To handle a delay while ascending to a decompression
and line.
stop (check all that apply):
a. if ascending to first stop, add delay to bottom b. to live with it as it is.
time and deco on new schedule. c. to wait for a support diver to reinflate it.
b. do not count delays between stops as decom- d. to send a team mate’s bag up on the same line
pression time. for additional flotation.
c. follow your computer’s schedule if you’re using
one.
Check it out:
d. it’s wise to extend your last stop as much as
1.a,b,c,d. 2. dive planning. 3. accelerated deco tables.
practicable.
4. a,b,c. 5. a,b,c,d. 6. a,b. 7. a,b,c,d. 8. a,b,c,d. 9. d.

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 Tec Objectives Thinking Like a Tec Diver IV
As tec diving continues to evolve, new technologies
Highlight or underline the and methodologies arise quickly. Competent tec div-
answers to these questions ers recognize that their learning never stops. Besides
as you find them:
continuing their education in diver training courses,
1. What do tec divers mean they avidly read dive magazines, underwater scien-
when they say they tific and technical literature, and other information
“never stop learning”?
sources that bring new developments into undersea
2. What four attitudes char- exploration.
acterize leading tec div-
ers? Successful tec divers pay attention to new ways of
doing things as they meet and interact with different
3. What is the biggest myth
told about diving with tec divers from different locals and environments.
certain methodologies or They analyze each dive after the fact and make a
in certain environments? conscious effort to distill new learning from it. Tec
4. Why is methodology situ- divers say “They never stop learning,” meaning that
ational? your education in technical diving never ends, and
that every tec dive is part of it.

Four Attitudes Characterize Leading Tec Divers

In considering your growth as a tec diver, it’s worth noting the
characteristics tend to typify leaders in not just tec diving, but in
most areas of exploration:
Humility. They realize that they don’t know everything, and that
there may be more than one right way to do something. Their ego
doesn’t get in the way of learning, doing or teaching.
Open Mindedness. They never reject something just because it’s
new or different, and they listen to other viewpoints. They don’t
fear change and they’re not threatened by differing opinions.
Analytical. They accurately and realistically weigh the merits of
a technology or procedures for themselves and never accept some-
thing just because it’s new or because someone else thinks it’s better
Competent. While they’re open to change and alternative ways to
do things, their own methodologies are solid and they can demon-
strate a rationale and realistic basis for each. They’re quietly confi-
dent about how they dive.

The Biggest Myth in Diving

The biggest myth in diving (tec or recreational) is that learning to
dive in a specific environment or with a specific methodology quali-

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 fies you to dive everywhere. There is no such
environment. There is no such methodology.
Methodology and its supporting technology
are, to varying extents, situational because
each situation imposes differing demands.
For instance, a three hour dive in 27°C/80°F
water wouldn’t require a dry suit, whereas in
10°C/50°F water it definitely would. Using a dry
suit, as opposed to not, dictates differing diving
techniques — so here at the most basic level
(you’re not even looking at tec diving specifi-
cally yet), methodologies differ.
The suggestion that mastering one methodol-
ogy or environment meets all diving circum-
stances presupposes that the methodology
addresses all possible variables, or that the
The suggestion that mastering one meth- environment imposes all possible variables.
odology or environment meets all diving This isn’t possible. A deep lake dive may be
circumstances presupposes that the meth-
odology addresses all possible variables, or very cold, dark and eerie, but it probably
that the environment imposes all possible doesn’t have the challenge of oceanic currents.
variables. This isn’t possible. No environ- Opposite conditions have their own challenges
ment can be both tropical and polar, lake
— no environment can be both tropical and

FOUR
and ocean, etc.
polar, lake and ocean, etc.
The basic methodologies and configurations you learn in this
course form the foundation for a wide variety of technical div-
ing circumstances. However, you must learn specifics for the tec
environment you actually dive from your instructor, the local tec
community and from experience gained by broadening your limits
slowly and carefully over many dives. And, when you go to tec dive
in another environment, as you’ve learned you’ll need to learn the
specific procedures and requirements for that environment.

Tec Exercise – 4.4

1. When they say they “never stop learning,” tec div- 3. The biggest ______ in diving is that learning to dive in
ers mean that your _____________ as a tec diver never a specific environment or with a specific methodologies
___________. qualifies you to dive __________.
2. F our attitudes that characterize leading tec divers 4. Methodology is situational because no environment can
include (check all that apply): impose all possible __________.
a. humility c. analytical
b. narrow mindedness d. critical

Check it out: 1. education, ends. 2. a,c. 3. myth, everywhere. 4. variables.

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 Performance Preview: Practical Application Four
Objectives During this practical application, you’ll work in teams
to plan Training Dives Six and Seven based on infor-
To successfully complete this mation your instructor provides. Consider A Good
Practical Application, you
will be able to: Diver’s Main Objective Is To Live and refer back to this
manual as you plan. They will both be gas-switch,
1. Working as a team, plan
extended no-stop dives. Dive Seven will include simu-
Training Dives Six and
Seven by appropriately lated decompression stops at 6 metres/20 feet and 3
and accurately account- metres/10 feet.
ing for logistics, runtime,
gas requirements for each Your instructor will provide the basis for determining
diver, OTUs, CNS% and your deco schedule and have you calculate, OTUs and
maximum depth based on CNS for each diver and gas, plus gas requirements
personal SAC rates, dive including one-third reserve, actual gas supplies, turn
profiles, gas blends to be points, equipment requirements, logistics, emergency
used, environmental details
procedures and other information from the A Good
and other information pro-
vided by the instructor as Diver’s Main Objective Is To Live planning process.
necessary about the dives.
Your plans should contain all information you would
need to make the dives.
You will also complete Exam One as part of your prac-
tical application. You must complete the exam independently (it’s
not a team exercise), and may use scratch paper, a calculator and
the tables in the appendix of this manual. Note that you will be
required to turn in the scratch paper with your calculations for the
dive planning problems. You must successfully complete the exam
prior to Training Dive Six.

A Word for the Apprentice Tec Diver

If you’re taking the Apprentice Tec Diver portion of the Tec Deep
Diver course, successfully completing Exam One and Training Dives
Six and Seven marks the end . . . for now. Congratulations for
accomplishing so much.
“Apprentice,” that is, “one who is learning,” tells you that the
Apprentice Tec Diver course is not, nor was never meant to be,
the completion of your training. Rather, the Apprentice Tec Diver
course opens the door for those who have the background to begin
training, but lack the qualifications to complete training.
Your Apprentice Tec Diver certification qualifies you to apply
some new skills. You’re qualified to use up to EANx60 to make
gas-switch, extended no-stop dives, and to pad your safety stops.

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 Obviously you’re qualified to make no stop dives in tec gear.
At the same time, it’s worth remembering that you’re not yet quali-
fied to make decompression dives, even though you’ve begun to
learn a bit about it. But there’s still more to learn, and more skills
to develop before attempting technical decompression dives. And,
by now you know better than to tempt fate by attempting dives
you’re not trained and qualified for.
Be patient. Gain experience in as many different environments as
you can. Listen and learn. When you complete the prerequisites
necessary for picking up here and completing the rest of the Tec
Deep Diver certification, you’ll be ready, and have the experience
you can apply.

Preview: Training Dive Six

Performance Objectives
To successfully complete this training dive, attaining neutral buoyancy, then ascend-
you will be able to: ing approximately 3 metres/10 feet and

FOUR
re descending to within one metre/three
1. Working in a team, plan the dive follow-
feet of, but not touching, the bottom by
ing the A Good Diver’s Main Objective Is
maintaining neutral buoyancy.
To Live procedure, and perform predive
checks following the Being Wary Reduces 5. As a team, deploy a lift bag, ascend along
All Failures procedure, the bubble checks its line and perform a 15 minute safety
and descent checks. stop/simulated decompression stop (gas
allowing) at 3 metres/10 feet.
2. Execute a real or simulated gas-switch,
extended no stop decompression dive. 6. While making a safety stop/simulated
decompression stop with a line as a ref-
3. Beginning approximately one to two
erence, perform the gas shutdown drill
metres/three to six feet off the bottom
while maintaining buoyancy control and
and neutrally buoyant, commence and
not ascending or descending from stop
swim at least 18 metres/60 feet sharing
depth more than one metre/three feet.
gas with the long hose, as both the donor
and receiver, without making any contact 7. Demonstrate time/depth/gas supply
with the bottom. awareness by recording on a slate the
time and SPG reading at each 15 minute
4. Respond to a simulated BCD failure by
interval.
switching to back up buoyancy control,

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 Predive briefing and gearing up

Training Dive Six

• Record depth and SPG reading at each 15 minute interval
throughout the dive.
Entry — appropriate for environment
Weight check (if needed)
Bubble check
Don stage cylinders at surface
Descent
Descent check
Stage cylinder at second level (if appropriate) — continue to deep-
est level.
Ascent to second level and NO TOX switch at interval
required by dive plan.
Long hose drill, no bottom contact
BCD failure drill
Free time in general area for experience and practice
Deploy lift bag from second level.
Ascend along lift bag line and make 15 minute safety/sim-
lated deco stop.
Air break practice — break for two minutes after 10 minutes.
Gas shutdown drill while neutrally buoyant at stop
Surface — remove stage cylinder at surface
Exit

Post Dive
Performance review
Disassemble and stow equipment
Log dive for instructor signature.

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 Preview: Training Dive Seven

Performance Objectives

To successfully complete this training dive, tion failure by completing the dive using
you will be able to: the back up system, as included in the
predive planning process.
1. Working in a team, plan the dive follow-
ing the A Good Diver’s Main Objective Is 5. As a team, deploy a lift bag and ascend
To Live procedure, and perform predive its line to 6 metres/20 feet, switch to a
checks following the Being Wary Reduces decompression cylinder following the NO
All Failures procedure, the bubble checks TOX procedure and make a 30 minute
and descent checks. safety/simulated decompression stop at
that depth.
2. Successfully perform a gas-switch,
extended no stop dive with a 30 minute 6. Perform the gas shutdown drill while
safety/simulated decompression stop at 6 neutrally buoyant without varying more
metres/20 feet. than one metres/three feet from the stop
depth.
3. Retrieve a stage/deco cylinder that has
been staged and while continuing to 7. Demonstrate time, depth and gas supply
swim, don it. awareness by writing the SPG reading
and depth on a slate a specific bottom
4. Respond properly to a simulated com-
time assigned by the instructor.
puter or primary decompression informa-

FOUR
Predive briefing and gearing up

Training Dive Seven

• Record depth and SPG reading at instructor-specified interval
throughout the dive.
Entry — appropriate for environment
Weight check (if needed)
Bubble check
Don stage/deco cylinders at surface
Descent
Descent check
Stage cylinders at deco level and at second level (if appropriate)
— continue to deepest level.
Group stays together and explores; free time.
Ascent to second level.
Retrieve stage cylinder on fly, NO TOX switch.

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 Free time in general area for experience and practice
Computer failure drill
Deploy lift bag from second level.
Ascend along lift bag line, NO TOX switch at 6 metres/20 feet —
30 minutes safety/simulated deco stop
Air break practice — break for five minutes
after 25 minutes.
Gas shutdown drill while neutrally buoyant at stop
Surface — remove stage/deco cylinders at surface
Exit

Post Dive
Performance review
Disassemble and stow equipment
Log dive for instructor signature.

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 Survival
depends on being able to suppress anxiety
and replace it with calm, clear, quick and correct
reasoning.
— Sheck Exley, cave diving pioneer,
1949-1994

C
hapter Five introduces new information to you,
but you should find it fairly easy to learn. At
this point, you’re refining what you know based
on what you’ve learned in previous chapters.
Some of what this chapter discusses will seem
like a review — that’s as it should be.

Chapter FIVE: The Refinements You’ll start out look-

ing at, yes, more

FIVE
about gas planning,
with an emphasis on oxygen, the “oxygen window,” and
why oxygen has so many advantages over EANx when
decompressing. After that, you’ll look quickly at the
techniques involved with making decompression dives
in a current, followed by handling the emergency of an
unresponsive diver at depth — something you’ve already
looked at to some extent in the discussion on how to
handle a convulsing diver underwater. Then you get more
on thinking like a tec diver, with a look at the rescue phi-
losophy and more on how your thinking can prevent prob-
lems. Finally, a section on mission planning takes you into
getting something done while you’re down there — the
whole point of what you’re learning to do!

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 Tec Objectives Gas Planning V
Oxygen Window and Accelerated
Highlight or underline the
answers to these questions
Decompression
as you find them: As you’ve learned, switching to a high oxygen EANx
1. What is the “oxygen win- or 100 percent oxygen when you decompress acceler-
dow”? ates your decompression time, largely because the
body consumes oxygen through metabolism and
2. How does the “oxygen
window” relate to accel- other reactions. It doesn’t contribute substantially to
erated decompression? DCS, so from a decompression point of view, it can
be ignored (within limits well within anything that
3. Why is it that when
decompressing with applies to real diving).
100 percent oxygen,
When you ascend, as you recall, the drop in ambi-
you can complete the
decompression time for a ent pressure causes a pressure differential (gradient)
3 metre/10 foot stop as between the pressure of the dissolved inert gas (nitro-
deep as 6 metres/20 feet gen) in your tissues and the pressure of the inert gas
without having to adjust in your lungs. This is what causes the nitrogen to dis-
your decompression time solve out of your tissues. However, as you know, you
for the depth change?
can’t ascend too far (on a decompression dive) or the
4. How do you use desk top ambient pressure drops so much that nitrogen may
decompression software form bubbles in your tissues before it can dissolve
and/or multigas comput-
harmlessly out through circulation and the lungs.
ers to calculate accelerat-
ed decompression dives? The shift to a higher oxygen gas or pure oxygen dur-
5. How do you plan back ing ascent and/or decompression, creates a higher
up decompression infor- gradient (pressure difference) between the dissolved
mation for an accelerated inert gas (nitrogen) in your tissues and in your lungs.
decompression dive?
This oxygen-derived gradient is called the oxygen win-
6. How do you choose dow. Oxygen contributes to DCS only minimally, so
which gas blends to the gas diffusion is one way — out of the tissues. This
use for an accelerated
is the basis for accelerated decompression.
decompression stop?
7. What are “deep stops,” This becomes really obvious if you look at it on an
how do you apply them, EAD basis. Suppose your first decompression stop is
and what might the ben- at 9 metres/30 feet. If you switch to EANx50 at that
efit be of doing so ? depth, your EAD is two metres/seven feet. Therefore,
nitrogen leaves your body as if you were only two
metres/seven feet deep breathing air. But, actually ascending that
shallow, would probably cause DCS.
This is more than a little bit of an advantage. From a practical
point of view, accelerated decompression reduces your exposure
to cold water and boredom. From a theoretical point of view, for a
given decompression model, the shorter the required decompression,
the more reliable it is. So, using EANx and oxygen to shorten your

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 required decompression reduces your theoretical risk. And, you can
enjoy these advantages while still padding your schedule to make it
more conservative. But, accelerated
decompression is never as conserva-
tive as switching to EANx or oxygen
while following a single gas (air)
decompression schedule.
Oxygen in Particular.
Decompression with 100 percent
oxygen offers some practical decom-
pression advantages over enriched
air. The greatest oxygen window
comes from breathing pure oxygen
(at 6 metres/20 feet and shallower
due to oxygen toxicity concerns, of
The greatest oxygen window comes from breathing pure oxy-
course). Note that with 100 percent gen; the EAD is always minus 10 metres/ minus 33 feet and
oxygen, the EAD is always minus you’re releasing nitrogen faster than if you were at the surface
10 metres/ minus 33 feet and you’re breathing air.

releasing nitrogen faster than if you

were at the surface breathing air. This means that using 100 percent
oxygen, for practical purposes you release nitrogen at the same
rate, no matter what your depth.
This means you have flexibility in choosing your decompression
stop depth. When using 100 percent oxygen, you can complete
stops that are supposed to be shallower than 6 metres/20 feet at
6 metres/20 feet without having to recalculate the decompression
time. With any EANx, a stop depth change alters the decompression
requirements. But, note that you cannot ascend from the 6 metre/20
foot stop earlier than scheduled just because you’re using oxygen.

FIVE
This can provide logistical advantages, because staying deeper
allows you to stay in calmer water if it’s rough, or below traffic if
you have unexpected boats criss-crossing above. You may have the
perfect decompression spot to rest and relax at 6 metres/20 feet, but
nothing at all at 3 metres/10 feet — so you just stay.
There’s also some theoretical benefit to staying a bit deeper than
the typical last stop of 3 metres/10 feet. Using 100 percent oxygen,
it’s typical to ascend to 5 metres/15 feet for the 3 metre/10 foot stop
time. This keeps you deeper than 3 metres/10 feet but drops the PO2
to keep your oxygen exposure somewhat more conservative com-
pared to 6 metres/20 feet. A 5 metre/15 foot stop has become com-
mon in place of the 3 metre/10 foot stop to the point that even when
not using oxygen, you can take your stop at 5 metres/15 feet when

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 using a dive computer, or by setting your desk top deco software to
create the final stop at 5 metres/15 feet instead of 3 metres/10 feet.
(This is why you’ve been making 5 metre/15 foot stops in training
dives.)
Planning Accelerated Decompression Dives. As you probably
know by now, to plan an accelerated decompression dive you’re
going to use desk top deco software and/or a multigas computer.
It’s much like calculating a gas-switch, extended no stop dive —
actually simpler with most desk top deco software.
With most software, you enter your bottom
depth, time and gas, and also enter the blend
or blends (or pure oxygen) you’ll use during
decompression. The software generates your
deco tables showing you gas switches, times, etc.
You compare depth/time possibilities until you
find the combination that’s workable with the
gases and volumes you have available. With a
multigas computer, you simply enter the gases
you’ll be using and then tell the computer when
you’re using what during the dive.
Watch gas supplies closely; you have a shorter
decompression compared to a single gas profile,
but you must have sufficient volume of each
deco gas to decompress adequately. It’s best to
have desk top deco software to estimate what
schedule you get from your multigas dive com-
puter, because with most multigas computers
there’s no way to easily determine what the deco
requirements will be.

When making an accelerated decompression If you’re stuck using a multigas computer with-
out desk top deco software, then plan your dives
dive with a multigas computer, you simply enter
the gases you’ll be using and then tell the com-
based on your back gas — planning as a single
puter when you’re using what during the dive.
gas dive with respect to the gas volumes you take
— but then noting the actual deco times on the
dive when you switch. Keep these in your log book and stick with
the same deco gases as much as possible. Over time, you’ll learn to
estimate how much you need to take of each gas to complete your
deco and still surface with one third of each gas remaining.
Again, with air, enriched air and oxygen, the optimum way to plan
an accelerated decompression dive is to use a multigas computer on
the dive and plan with desk top deco software.

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 Making Accelerated Deco Dives More Conservative. Although
accelerated decompression gives up the “pad” of basing your dive
on a single gas computer or table and then switching to higher
oxygen, you can still pad your schedule for added conservatism.
When following tables generated by desk top deco software you
can:
• use the tables for the next greater depth and/or time than actu-
ally called for.
• generate the tables based on blends with less oxygen than actual
(note that you will need to determine actual max depths and
oxygen exposure).
• make a safety stop within the last decompression stop.

When using a multigas computer you can:

• set the computer for an altitude higher than actual.
• set the blends for less oxygen than actual (note that you will
need to determine actual max depths and oxygen exposure
yourself)
• stay well within all limits given by the computer.
• make a safety stop within the last decompression stop.
Planning Back Up For Accelerated Decompression Dives. A draw-
back to an accelerated deco dive compared to one based on a single
gas is that you must have your deco cylinders to decompress. This
adds another dimension to contingency planning. At the simplest,
you can use desk top deco software to write alternative emergency
tables for doing your hang without your deco cylinders. With multi-
gas computers, you simply stay on the blend you’re using.
In lost gas situations, however, it’s quite possible that you won’t
have enough gas to complete your decompression. If so, account-

FIVE
ing for this and planning for it is crucial in going through A Good
Diver’s Main Objective Is To Live. If there’s any doubt, it’s less risk
to keep your deco cylinders with you because you must have them.
In some instances, you can plan your dive as a single gas dive and
take sufficient back gas to complete the decompression. Then, you
dive following the accelerated decompression schedule; if you have
a problem, your contingency plan is to use the single gas schedule.
Choosing Deco Blends. Using desk top deco software, you’ll find
that the shortest decompression comes from switching to the high-
est possible oxygen at each stop. If you have four stops, that would
mean four different gas blends — but that’s usually impractical
and you usually don’t gain much for having to haul four cylinders
instead of one or two.

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 For dives to 50 metres/165 feet, you seldom benefit much by having
more than two deco blends. For shorter dives, a deco single cylinder
may be fine. Remember the KISS (Keep It Super Simple) principle
— simpler is usually better, especially if taking one cylinder ver-
sus two, or two versus three, only means a few more minutes deco
time. It’s that much less to haul and deal with. Remember that you
and your team mates want to use the same or compatible blends.

Deep Decompression Stops

In recent years, anecdotal evidence suggests that
planning a deeper stop than normally required
when making a decompression dive enhances the
effectiveness of the decompression. This is a called a
deep stop. While this appears to relate most directly
to diving with helium blends, the practice has been
adopted by most tec divers even when making air
and enriched air dives.
You make a deep stop for two min-
45/150 utes at the halfway point between
28.5/95 (ascent) the bottom depth and the first
28.5/95 (deep stop)
“required” deco stop. For example,
if you were diving at 45 metres/150
12/40
feet and your first stop is at 12
9/30 metres/40 feet, you make a deep
6/20 stop at 28.5 metres/95 feet. Note
3/10 that this exactly the same way you
find the midpoint you use for calcu-
lating your ascent from the bottom
45/150
to the first required stop.
37/122 (ascent to deep stop)
Listing your deep stop and ascent at the
If you make your deep stop on your
28.5/95 (deep stop)
midpoint between your bottom depth and bottom gas, you typically list the
the first stop. ascent and the deep stop separately 20/67 (ascent to 40 feet)
(different SAC rates) on the dive 12/40
planning workslate, though the same depth. 9/30
If you make a gas switch at the deep stop, calcu- 6/20
late ascent based on the midpoint from the bot- 3/10
tom to the deep stop, then the midpoint between
the deep stop to the first required stop. (See exam-
ple) This gives you three different depths between
Listing your ascent as midpoints
the bottom and the required stop. Do this if you
between the bottom depth and the
change gases at your deep stop, which affects your deep stop, and the deep stop and the
oxygen exposure and gas requirements. first stop.

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 Some desk top deco software will
automatically add deep stops if
you want. If not, you must enter
the deep stop as a way point in the
profile it calculates. Don’t make
a deep stop unless it’s in your
schedule because, on a decompres-
sion model level, you’re taking up
nitrogen in slower compartments
that you’ll have to account for on
shallower stops. Dive computers
automatically account for this on Some desk top deco software will automatically add deep stops if
deep stops when you make them. you want. If not, you must enter the deep stop as a way point in
the profile it calculates. Don’t make a deep stop unless it’s in your
schedule because, on a decompression model level, you’re taking
up nitrogen in slower compartments that you’ll have to account for
on shallower stops.

Tec Exercise – 5.1

1. The oxygen-derived gradient that accelerates nitro- 4. To calculate an accelerated decompression dive (check all
gen diffusion out of your body is called the _________ that apply):
_______. a. you enter the gases you’re using into desk top deco
software and/or a multigas computer.
2. The __________ _________ is what makes _________
b. you use the EADs of each deco depth on a single
_________ possible.
gas table.
a. oxygen window, nitrogen uptake
c. you must assume you’ll only have one decompres-
b. oxygen window, accelerated decompression sion gas.
c. nitrogen window, nitrogen uptake d. None of the above.
d. nitrogen window, accelerated decompression
5. To back up your deco information for an accelerated
3. When decompressing with 100 percent oxygen, you decompression dive, at the simplest, you can use desk

FIVE
can complete the decompression time for a 3 metre/10
top deco software to write alternative __________
foot stop as deep as 6 metres/20 feet without having to
adjust your decompression time for the depth change ________ for doing your hang without your deco cylin-
because (check all that apply): ders.
a. your EAD is always minus 10 metres/minus 33 feet, 6. When choosing which gas blends to use for an acceler-
b. there is no oxygen window above 6 metres/20 feet. ated decompression dive (check all that apply):
c. oxygen is more narcotic than nitrogen. a. remember the KISS principle.

d. breathing pure oxygen, for practical purposes you b. there may be little real benefit to taking one more
lose nitrogen at the same rate regardless of depth. gas blend.
c. you and your team mates need to choose compati-
ble blends.
d. None of the above.

Check it out: 7. At its simplest, a deep stop is a stop made for ______
1. oxygen window. 2.b. 3. a,d. 4. a. 5. emergency tables 6. _______ at the _________ point between the bottom
a,b,c. 7. two minutes, halfway, required deco stop. depth and the first _______ ______ _______.

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 Tec Objectives
Techniques IV
Decompressing in Currents.
Highlight or underline the Much of what you’ve already learned and practiced
answers to these questions
as you find them: involves diving in currents, making stops in them,
and emergency procedures. These include using jon
1. What are some of the
lines, lift bag procedures, descending and ascend-
procedures and con-
siderations for making ing along lines (boat, mooring, lift bag), carrying
decompression dives in a a drift kit, not staging cylinders if a current can
current? keep you from returning to them, and using boat
2. What is a “drift hang” lines such as swim lines and trail lines like you use
and what are the advan- in recreational diving. Some of your training dives
tages and disadvantages may have involved some current. From previous
of it? discussions you know that before making decom-
pression dives in an area with currents, you should
gain experience and be thoroughly familiar with the
local techniques by making no stop dives first. It’s easy to overex-
ert yourself trying to out swim a current wearing just recreational
equipment; in tec gear it’s even easier. Use your brain, not your
back, to work a current.
Drift Hangs. Decompressing in a current is a pain in the rump.
Even using a jon line, it’s often tiring, especially when you’re in
strong current and have a long hang. In some situations you don’t
have a choice, so you deal with it.
But often an alternative is a “drift hang” (also called “blue water
decompression”) in which divers decompress along a line from a
float or boat while adrift in the current. The procedures vary, but in
general:
1. All divers return to mooring/anchor line and start decompression
maintaining place in current.
2. The boat lowers (or has in place) a weighted line.
3. On signal, support divers release the boat from the mooring/
anchor, and all divers swim to weighted line while maintaining
their stop depth.
4. Divers complete decompression on the weighted line.
There are variations, such as the breakaway hang. In this case,
the team releases a line with a float ball from a mooring or other
anchor point. Team decompresses drifting with the boat following
the float ball. Essentially, decompressing under your lift bag, as
either a planned primary procedure or as a back up procedure, is a
variation of the breakaway hang.

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 Drift hangs have several
advantages, the first being
that once you’re adrift, for
all practical purposes there
is no current. Everyone
moves with the water, so it’s
much more restful. Another
advantage is that it’s easier
to maintain your stop depth.
And, if you have surface sup-
port they can more easily
take your unneeded gear, or
bring down extra gas, etc.
Drift hangs do have some
Drift hangs have several advantages, the first being that once you’re adrift,
disadvantages. First, they for all practical purposes there is no current. Everyone moves with the
require close coordination water, so it’s much more restful. Another advantage is that it’s easier to
of all teams in the water. maintain your stop depth.

Second, is that typically,

everyone must dive together — you often can’t stagger teams com-
ing out and going in (this isn’t an absolute — in some areas, there
are ways to do this, though this isn’t typical). Another potential
issue is that waiting for one diver can hold up the drift for several
teams; procedures need to include actions for disoriented div-
ers (usually requires sending up a bag and drifting under it) and
accounting for them by surface support. You almost always have
to have surface support, at least minimally. Finally, you need to
account for how far and in which direction you’ll drift so you don’t
get pushed into sea lanes (ship traffic hazard) or water too shallow
to decompress in.

Tec Exercise – 5.2

FIVE
1. Before making decompression dives in an area with 2. Disadvantages of a drift hang include (check all that
currents, you should gain experience and be thor- apply):
oughly familiar with the _______ _______ by making a. that they need close coordination.
_____ _____ dives first. b. one diver can hold up the entire drift hang.
c. you almost always need surface support.
d. you have to beware of which way and how
Check it out: far you’ll drift.
1 local techniques, no stop. 2. a,b,c,d.

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 Tec Objectives Emergencies V
As discussed earlier with respect to a diver who
Highlight or underline convulses underwater, an unresponsive diver at
the answers to this depth is one of the most serious emergencies you
question when you can face. Having required decompression makes
find them:
a rescue complicated. As a technical diver, you accept the
1. What is the prior- risk and responsibility that something could cause you to
ity and how do become unresponsive, and that decompression require-
you respond to an
unresponsive diver
ments and the distance from the surface may make it diffi-
at depth during a cult or impossible to effect a rescue before you drown.
decompression dive?
If a team mate becomes unresponsive, the priority is get-
ting the victim to the surface (but remember the recom-
mendation is to wait for a convulsing diver to finish the convulsion).
Hold the regulator in if it is in and the victim is breathing. If you need to
tow the victim underwater to an appropriate ascent area to make a res-
cue possible (due to current, proximity of surface support, etc.), make the
victim neutrally buoyant and hold the mouthpiece in while towing.
As soon as possible, get the victim to surface. Take the diver up yourself
if possible and if, based on your decompression situation, you judge the
risk of DCS isn’t excessive. As discussed earlier, the recommendation is to
not drop the victim’s weights until reaching the surface so that you don’t
put yourself at risk from an uncontrolled ascent. Try to maintain a neu-
tral airway that allows expanding gas to escape from the diver’s lungs.
Signal surface support divers if available. If you owe a lot of stop time,
but other divers completing or almost complete with their decompression
are present, they may be able to take over the rescue with minimal DCS
risk.
Whether to risk DCS yourself is a difficult call, but one you may have to
make. If you owe relatively little decompression, the victim is breathing
and has the regulator in, and there’s assistance at the surface, the prob-
ability of the victim surviving is high and the probability of severe DCS
is low. If you have a lot of decompression due, the victim is unbreathing
and unresponsive and has been for some time, and there’s little or no
surface support, the DCS risk is high and the probability of bringing the
victim back low.
As you know from your PADI Rescue Diver course, there are no hard
rules — you can only make the best decision you can given the circum-
stances. Remember that you shouldn’t take unreasonable risks yourself to
help the victim — if you’re in trouble, you can’t help anyone else.

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 Tec Exercise – 5.3

1. If a team mate becomes unresponsive, the priority is

______ ____ _______ _____ _________ ________.

Check it out:
1. getting the victim to the surface.

Thinking Like a Tec Diver V

The previous discussion made it clear that in tec diving as in rec-
reational diving, you don’t always have easy answers in an emer-
gency. You have to make decisions, not only about how to help
someone, but even if you will help someone — because you don’t if
it will put you at unacceptable risk. Professional rescuers sometimes
call this “Better thee than me.”
To the uninformed, “better thee than me” might sound uncaring
or mercenary, but the reality is the opposite for both you and the
victim: You can’t help someone if you’re in
trouble, too. You can’t even go get more help.
Tec Objectives When help does show up, two divers in trouble
splits the emergency resources.
Highlight or underline the In team tec diving, a similar situation may
answers to these questions
as you find them: arise in which a team mate enters a situation

FIVE
that poses an unacceptable risk for you. You
1. Professionals involved
may have to decide whether to accept the risk
with rescue sometimes
cite the philosophy, to help your team mate manage it, or whether
“Better thee than me.” to leave your team mate to manage solo. As
What does this mean and a team member, you accept that you will take
how does it apply to tec some risk (tec diving involves risk) for each
diving?
other.
2. How do you plan for
“specific” mistakes and But, at the extreme it is better to have only one
emergencies? diver hurt or dead than two or three. Should
you take the risk? As with the unresponsive
diver, there are no hard rules, only hard deci-
sions. You’ll have to use good judgment and make the best decision
you can under the circumstances.

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 Foreseeing the Foreseeable
Most of your training in the Tec Deep Diver course prepares you
for common, reasonably foreseeable risks in deep tec diving to 50
metres/165 feet. But that’s not all there is to it. Skilled tec divers
learn to look at each dive and plan for reasonably foreseeable mis-
takes and emergencies specific to that dive.
This isn’t that hard. For example, in poor visibility, you note that
team separation is a foreseeable mistake and agree on what to do
if it happens. In current, you realize that you may have to work
harder, causing higher gas consumption that you have to prepare
for. In cold water, you plan for the problems of working your gear
with thick gloves and some narcosis. Diving in a new environment
raises reasonably foreseeable issues. Haven’t worn cold water gloves
in awhile? Then maybe you should practice with them in the pool
before making a tec dive in them. Been diving in cool water dry
and now you’re going to make a tropical tec dive in a wet suit?
Then maybe you should gear up and get wet in a pool or controlled
conditions in that configuration before making the tec jump.
Teach yourself to be specific to the dive when covering A Good
Diver’s Main Objective Is To Live. You do this by asking, as you
already learned, “What about this can hurt or kill me?” Before you
dive, have a way to handle every reasonable problem you come up
with.

Tec Exercise – 5.4

1. The “better thee than me” philosophy considers that 2. Planning for “specific” mistakes and emergencies
(check all that apply): (check all that apply):
a. staying out of trouble yourself is best for the vic- a. is handled by looking at possible mistakes and
tim, too. emergencies specific to each dive.
b. you may have to judge whether the risk of help- b. is not necessary because fundamental training
ing someone is acceptable. covers it.
c. you should take no risk at all for someone else. c. is really not practical.
d. you have to make the best decision you can d. is something that asking “What about this can
under the circumstances. hurt or kill me?” helps you do.

Check it out:
1. a,b,d. c is incorrect — you want to avoid unacceptable risk when helping someone, not necessarily all risk. 2. a,d.

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 Mission Planning Tec Objectives
“Main” in A Good Diver’s Main Objective Is To Live
stands for “mission.” This is your dive objective, Highlight or underline the
which is usually more than simply going for a look. answers to these questions
as you find them:
Without a mission, you’re nothing more than an
underwater gear manager — and that accomplishes 1. What is your dive “mis-
nothing. You’ll quickly find it unsatisfying. The sion” and why do you
have one?
whole point of learning to tec dive is so you can do
something. Possible missions are limitless, but some 2. Where does your dive
examples are: mission “objective” rank
in priority with the other
• Checking out new sites to see whether they’re aspects of a tec dive?
worth further exploration. 3. What is the most com-
• Mapping (ships, caves, reefs) mon mistake in mission
planning?
• Recovering something. 4. How can you simplify a
• Photo/video. dive mission?
5. How does mission plan-
• Taking samples/recording observations (science
ning usually affect dive
related) planning?
• Evaluating equipment or procedure performance
for future application.
• Team practice for a more complex dive.
Your dive has a mission for two primary reasons: First, it helps
assure that the dive is worth the time and money you put into it.
Second, it coordinates the dive team’s planning and dive execution
by providing a common purpose. Those are pretty good reasons
to have a mission — but guess what: the mission ranks last amid
all other dive planning considerations. As you learned, everyone

FIVE
returning unharmed is the first priority on a tec dive. Or put anoth-
er way, a good diver’s main objective is to live. (That should sound
familiar.)

Mission Planning
The most common mistake in mission planning, and the most
common reason missions fail, is trying to accomplish more than is
reasonable in a single dive. Since tec diving is itself complex, missions
must be simple and realistic.
It’s easy to recognize the need to simplify when the objective is
obviously broad and complex, such as “map an entire shipwreck.”
For a major wreck, that’s not a dive — that’s not even a couple
dives. It may be a dive season worth of dives.

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 The ones that trip you up are the ones that
are more complex than they sound. “Locate
and recover a flooded DPV abandoned at 50
metres/165 feet” may not sound complex at
first. But it is.
Simplifying Your Mission. The key to simpli-
fying is analyzing the objective and deter-
mining the subtasks it involves. If there are
few and they’re simple, then maybe it’s rea-
sonable to accomplish in a single dive. On
the other hand, you may find that each sub-
task is a project requiring its own dive, or a
separate team. For instance, bringing up the
DPV might require 1) a search, 2) rigging the
flooded DPV to lift and 3) actually bringing it
up. That may be two dives.
After breaking into subtasks, you have
to consider whether subtasks are simple
enough. Subtasks may have subtasks.
Simplify by planning subtasks as dive mis-
sions based on time and what a team can
reasonably accomplish on a single dive. As
The key to simplifying is analyzing the objective and
determining the subtasks it involves. If there are few appropriate, divide subtasks among team
and they’re simple, then maybe it’s reasonable to members, according to qualifications. Or,
accomplish in a single dive. On the other hand, you divide subtasks among different teams, or
may find that each subtask is a project requiring its
own dive, or a separate team. accomplish the objective by handling the
subtasks as several missions on several dives.
If you can, organize so that a team can leave
in mid-task and resume (or have another team resume) where they
left off.
Don’t forget that another way to simplify the complex is to train
for it. If you can’t break a mission into separate subtasks, your
team rehearses what it’s going to do (perhaps in shallow water)
until it’s down pat.

Mission Planning Amid Dive Planning

You’ll find that a clear mission usually simplifies dive planning
because it determines depth, time and location. Your team has a
focus, so it’s easier to reach a consensus about logistics, emergency
plans, etc.

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 At times, logistics and conditions will change the mission. For
example, when recovering the DPV with two dive teams, you plan
to have one team search and the second team recover. But on the
day of the dive, you find the visibility half its usual clarity, mean-
ing the search will be more difficult and time consuming than
expected. You revise the mission so both teams go in for the search,
with the recovery rescheduled for the next day.
Beware of Task Focus Instead of Dive Focus. Your/the team’s
attention should always be on the dive first, the mission second.
The dive ends at the required turn time or turn pressure, no matter
how close or far from accomplishing the mission. This can be frus-
trating if you’re so close to finishing you mission that if you push
into your reserve just a hair. . . . Don’t. This is where discipline
comes in. Your first priority is the dive plan, not the mission. A
good diver’s main objective is to live.

FIVE
Tec Exercise – 5.5

1. You have a mission because without it, you’re nothing 4. The key to simplifying is analyzing the objective and
more than an underwater _______ _______. determining the _________ it involves.

2. The mission ranks _____ amid all other dive planning 5. A clear mission usually _________ dive planning.
considerations.

3. The most common mistake in mission planning is try-

ing to accomplish _______ ______ ______ ______ in a Check it out:
single dive. 1. gear manager. 2. last. 3. more than is reasonable. 4. sub-
tasks. 5. simplifies

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 Performance Preview: Practical Application Five
Objective This Practical Application gives you hands on experi-
ence calculating and comparing the practical and
To successfully complete this
theoretical advantages and disadvantages of using
Practical Application, you
will be able to: differing gas combinations for the same accelerated
decompression dive. You’ll work with desk top deco
1. Working as a team, plan
and compare the decom- software, or if it’s unavailable, with tables derived for
pression requirements, accelerated decompression dives.
oxygen exposure and gas
You’ll calculate several versions of a dive to 50
requirements for several
possible ways to execute an metres/165 feet for 45 minutes, assuming switches to
accelerated decompression the deco gases at the depth where the blend has a PO2
dive based on a dive profile of 1.6 ata (rounded to the next shallowest “normal” 2
to 50 metres/165 feet for metre/10 foot stop depth is acceptable).
45 minutes.

You’ll calculate and compare this dive made with:

• Air , EANx32 and EANx40
• EANx23, EANx32 and EANx40
• Air, EANx36 and EANx80
• EANx23, EANx36 and EANx80
• Air, EANx36 and oxygen
• EANx23, EANx36 and oxygen
• Air, EANx50 and oxygen
• EANx23, EANx50 and oxygen
Your instructor will have you provide a printed/written analysis of
the decompression requirements, gas requirements based on your
personal SAC rates, the CNS clock and OTUs for each scenario.
Be prepared to discuss the trade offs and relative pros and cons of
the different gas blend combinations when used for this dive. Your
instructor will want to know:
• Which combination produced the shortest and longest dive
times?
• Which gas seemed to be least useful, for this dive, in providing
an advantage.
• Would you need more than one cylinder of the same gas in
some of the profiles you calculate?
• Would you use so little of one gas that it hardly seems worth the

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 trouble to carry it? Does it help to change the ranges over which
you use each deco gas (switch to higher oxygen gas shallower so
you use a deeper deco gas longer).
• Which combination would you choose in cold water?
• Is there a significant oxygen exposure advantage? What if you
were making several dives like this over several days in a row?
• Is there a cost advantage, such as using air instead of EANx23
with little increase in deco time?

Performance
Preview:
Objective Practical Application Six
During this practical application, you’ll work
To successfully complete this
in teams to plan Training Dives Eight and Nine
Practical Application, you
will be able to: based on information your instructor provides.
Consider A Good Diver’s Main Objective Is To
1. Working as a team, plan
Live and refer back to this manual as you plan.
Training Dives Eight and
Nine following the A Good Dive Eight will be a simulated accelerated decom-
Diver’s Main Objective Is To pression dive based on depth and time your
Live procedure, including instructor will provide (you actually make the
mission planning in Dive dive within the no stop limits).
Nine, based on the dive
specifics (depths, environ- Dive Nine will be your first actual decompression
ment, etc.) and mission pro- dive, made based on using a single gas table/
vided by the instructor. computer, with a single decompression gas as a
pad for conservatism. You should plan the dive
requiring only a single stop at 3 metres/10 feet or
5 metres/15 feet. If it will be a repetitive dive to Dive Eight, you’ll

FIVE
need to account for residual nitrogen and oxygen exposure. (OTUs
may be a factor for both dives if you’ve been diving for several days
in a row.)
Dive Nine will also have a mission component that your instructor
will assign. Your dive plan should include how you will attempt to
accomplish this mission. Note: Since the mission is your last prior-
ity, you do not necessarily have to complete the mission. If you’re
unable to complete the task, your instructor will consider how effec-
tive you and your team were amid the other dive requirements.
Accomplishing as much as would be reasonably possible without
violating safety guidelines or the dive plan is what your instructor
will be interested in. When working on this mission and future mis-
sions, pay attention to narcosis; this is an opportunity to learn how
narcosis can affect you, even if you don’t “feel narked.”

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 Your instructor will provide the basis for determining your deco
schedule and have you calculate, OTUs and CNS for each diver and
gas, plus gas requirements including one-third reserve, tank base
lines, turn points, equipment requirements, logistics, emergency
procedures and other information from the A Good Diver’s Main
Objective Is To Live planning process.
Your written plans should contain all information you would need
to make the dives.

Preview: Training Dive Eight

Performance Objectives

To successfully complete this training dive, sion dive, making appropriate NO TOX
you will be able to: gas switches as necessary to follow the
schedule.
1. Working in a team, plan and execute a
simulated accelerated decompression 5. As a team, respond properly to a failed
dive following the A Good Diver’s Main lift bag/lift bag line by maintaining stop
Objective Is To Live procedure, and per- depth while deploying a second bag,
form predive checks following the Being and completing the simulated decom-
Wary Reduces All Failures procedure, the pression.
bubble checks and descent checks.
6. Perform the gas shutdown drill while
2. Tow a simulated unresponsive, breath- neutrally buoyant at the stop depth
ing diver 6 metres/20 feet horizontally while not varying more than one metre/
underwater. three feet from the stop depth.
3. Perform the gas shutdown drill on the 7. Demonstrate time, depth and gas supply
bottom in 45 seconds. awareness by recording the depth and
time on a slate upon reaching a back gas
4. Decompress following the schedule for
pressure assigned by the instructor.
a simulated accelerated decompres-

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 Predive briefing and gearing up

Training Dive Eight

• Record depth and time reading upon reaching an instructor-
specified back gas pressure.
Entry — appropriate for environment
Weight check (if needed)
Bubble check
Don stage/deco cylinders at surface
Descent
Descent check
Stage deco cylinders
Unresponsive diver tow at depth — 6 metres/20 feet
Gas shutdown drill — 45 seconds
Retrieve and don deco cylinders
Free time as bottom time and gas allows
Deploy lift bag — ascent, NO TOX switch and begin simulated
accelerated decompression
Failed bag drill
Continue decompression — air breaks
Gas shutdown drill while neutrally buoyant
Surface — remove stage/deco cylinders at surface

FIVE
Exit

Post Dive
Performance review
Disassemble and stow equipment
Log dive for instructor signature.

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 Preview: Training Dive Nine

Performance Objectives

To successfully complete this training dive, mission, carrying it out to the team’s
you will be able to: ability within the limits of the dive plan.
1. Working in a team, plan and execute a 3. Demonstrate time, depth and gas sup-
decompression dive based on a single ply awareness by recording the depth
gas table or computer with an enriched and time upon reaching an SPG read-
air blend for added conservatism follow- ing assigned by the instructor, and by
ing the A Good Diver’s Main Objective Is recording the depth and SPG reading
To Live procedure, and perform predive upon reaching a bottom time assigned
checks following the Being Wary Reduces by the instructor.
All Failures procedure, the bubble checks
and descent checks. 4. Perform a timed task at the surface, and
then again at depth, to observe the
2. Working in a team execute the dive’s effect of narcosis.

Predive briefing, timed task at surface, and

gearing up

Training Dive Nine

Deploy lift bag — ascent, NO TOX
• Record depth and time reading upon reaching
switch and begin simulated accelerated
an instructor-specified back gas pressure, and
decompression
record depth and SPG reading upon reaching
a bottom time assigned by the instructor. Ascend, retrieve deco cylinder (if staged)
and decompress with NO TOX switch at
Entry — appropriate for environment
5 metres/15 feet or 3 metres/10 feet —
Weight check (if needed) air breaks.
Bubble check Surface — remove stage/deco cylinder at
Don stage/deco cylinder at surface surface

Descent Exit

Descent check Post Dive

Stage deco cylinder at deco level Performance review
(if appropriate) Disassemble and stow equipment
Gas shutdown drill Log dive for instructor signature.
Mission objective — timed task

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 Instructor Guide 45 Handouts Tec Deep Diver
Digital Manual

Appendix

Tec 45
Other Delivery Content, Tec 45-1
Study assignment: Tec 45 Handout 1

Learning Objectives
By the end of this section, you should be able to answer these questions:
1. Why is the standard practice to use two multigas dive computers on the dive, and to plan
with desk top decompression software?
2. Why are DSMBs replacing lift bags in many tec diving situations?
3. Why has failure of quick releases on harness shoulders proved not to be a serious issue?
What would you do if it were to happen?
4. What is perhaps the most common weighting error in tec diving?
5. Why is backup buoyancy critical in most open water, open circuit technical diving?
6. What are the problems with trying to use a lift bag or DSMB as a backup buoyancy system?
7. What is the policy of virtually every lift bag and dry suit manufacturer with respect to
backup buoyancy?
8. Why is the redundant (double bladder) BCD the most realistic approach to providing
backup buoyancy control?

A. The standard of practice in deep decompression tec diving is to use multigas dive
computers during the dive, with decompression software for overall planning. You
may use a single gas computer and/or depth gauge and timer with tables in this
course, but this is the recommended approach. There are several reasons why:
1. Multigas computers now handle up to seven gas mixes (including trimix),
and also calculate CCR (closed circuit rebreather) diving, making them suit-
ed to your future as well as present tec diving.
2. A multigas computer maximizes your options in an emergency, allowing
you, for example, to switch to a lower oxygen gas (even back gas) should
you lose or exhaust your primary deco gas.
a. Some of the newest models allow you to enter entirely new gases
during the dive and recalculate your decompression. This provides
more options in an emergency.

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3. Many multigas computers have PC interfaces, allowing you to adjust stop

depths, conservatism factors, etc. Some let you choose the decompression
model you prefer.
4. Multigas computers track your actual dive profile, adjusting your decom-
pression requirements based on your actual dive. This makes it easier to
adjust to circumstances. Example: You accidentally exceed your planned
depth slightly; you leave the bottom sooner based on your computer so that
your decompression time is the same as planned, keeping you within your
gas plan.
5. With a multigas computer, you can choose to decompress based on a single
gas and switch to a higher oxygen gas for added conservatism (as you
learned to do as a Tec 40 diver). Should circumstances require (emergency),
however, you can switch to accelerated decompression to get to the surface
faster with less gas used.
6. You still use deco software to plan the dive – oxygen exposure, decompres-
sion and gas requirements. Use the computer within the dive you plan.
7. Multigas computers are more sophisticated than single gas, so they’re more
complex to use. But, they are not difficult to use and getting easier.

B. DSMBs (Delayed Surface Marker Buoys) are replacing lift bags in many tec diving
situations.
1. DSMBs stand higher in the water, making them preferred for rough condi-
tions.
2. DSMBs are more compact on your rig, making them popular when used as
an emergency alert only.
3. DSMBs have no-spill designs (though several lift bags have these, too,
now), so accidentally losing tension on the line isn’t likely to result in a
spilled buoy.
4. The highest capacity DSMBs are essentially tall, thin lift bags and work
well for drift decompression.
5. Several types of DSMBs (and lift bags) have LP inflation ports that allow
you to fill them with an LP inflator hose, away from your body or mouth,
without using a second stage. This minimizes the chance of regulator freeze,
as well as minimizing reel tangle issues.

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C. At one time, some people thought failure of shoulder quick release buckles on tec
harnesses would be a serious issue. This hasn’t proven true.
1. Quick release buckles are designed to withstand hundreds of kg/lbs direct
stress. This explains why stress failure is virtually unheard of.
2. Were the release to fail, you would only have to pass the lower part of the
harness strap through the D-ring on the upper part and tie it.

D. Weighting
1. Proper weighting and adequate backup buoyancy remain two areas com-
monly addressed inadequately in open circuit technical divers.
2. Perhaps the most common weighting error in tec diving is under weighting.
a. Proper weighting means you’re able to maintain your final stop
depth with nearly empty back cylinders and either no or near-empty
deco cylinders – this is what would happen if you had a major prob-
lem forcing you into a long deco using your gas reserve, and/or
decoing on back gas.
b. If you were not weighted for this, you face a high DCS risk, because
you would not be able to remain at stops.
c. As an example, a properly weighted tec diver wearing high capacity
doubles and two deco cylinders will be about 14 kg/30 lbs negatively
buoyant at the start of a dive, and 4.5 kg/10 lbs or more negative at
the end if dive goes as planned.
d. In this example, inadequate weighting would mean that in an emer-
gency situation, besides the original problem, you also have to deal
with between 4.5 kg/10lbs and 14 kg/30 lbs positive buoyancy while
trying to decompress.

E. Backup buoyancy is critical in most open water, open circuit technical diving
because a diver is substantially negatively buoyant throughout the dive.
1. Failure of the primary BCD without a backup leaves no alternative but to
drop equipment (deco cylinders, weights, etc.). This can make the situation
worse if the diver must discard deco gases to attain buoyancy.
2. Discarding gear may result in too much buoyancy. If the diver is already in
deco, the ability to decompress effectively becomes compromised, growing
worse as the diver consumes gas.

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3. There is a high likelihood of surfacing with omitted decompression if the

diver cannot maintain stop depths, or lacks the required decompression
gases, or both.
4. A dry suit may work as a backup buoyancy device.
a. This is primarily an option when the dive will be relatively short and
shallow, with short decompression – the gas requirement is low, so
the diver is not substantially negatively buoyant (such as when using
aluminum cylinders).
b. Limited option – most dry suits will not hold more than small
amount of excess gas. Beyond a certain point, it escapes through
neck/wrist seals.
c. Several manufacturers caution against inflating their dry suits to gain
large amounts of buoyancy because of zipper failure issues.
d. A large volume of expanding gas is harder to control in a dry suit.
e. With deeper/longer tec dives, backup buoyancy control other than
the dry suit is generally necessary.
5. Some have advocated using a lift bag or DSMB as a backup buoyancy
device. This has several problems:
a. DSMBs and lift bags are not designed as buoyancy devices and are
difficult to control in that role.
• They are even more difficult to control while trying to per-
form gas switches, handle a gas shutdown, etc.
• Even if learned and practiced, it is not a skill one would
expect a diver to perform reliably in a real failed BCD emer-
gency over the course of a real decompression. If it has not
been practiced at all, it would be especially difficult.
• DSMBs/lift bags do not provide a realistic buoyancy system
for positive buoyancy at the surface after completing decom-
pression.
• Using a DSMB/lift bag as back up buoyancy would require
the diver to hold on to the bag while dealing with other tasks,
or it would have to be clipped to the harness. Either would
compromise safety.
b. If the DSMB/lift bag is used for backup buoyancy, then it is not
available to send to the surface.

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c. Sending the DSMB/bag to the surface and hanging on the line for
buoyancy is not a good option either.
• In all but flat seas, this will cause the diver to rise and fall,
compromising the quality of the decompression.
• Once sent up, there is no way to adjust the bag’s buoyancy.
• It is not a technique that transfers well to other environments.
• Stress on the line and reel is a major issue. For this to be reli-
able, the diver would need to carry much heavier line and a
larger reel than most tec divers prefer.
d. Trying to use a lift bag or DSMB as a backup buoyancy system
unnecessarily complicates an emergency situation, and provides
inadequate benefit.
6. It’s worth noting that no dry suit manufacturer and no lift bag manufacturer
sanctions the use of their products as tec diving backup buoyancy devices.
Some specifically warn against it.
7. The redundant (double bladder) BCD is the most realistic approach to pro-
viding backup buoyancy control.
a. They are designed for the job and endorsed by the manufacturers.
b. They are used the same way as your primary BCD – a well practiced
skill you use on every dive, exactly what you want in an emergency
situation.
c. They are applicable to virtually all dive environments.
d. Other than a slightly higher investment, there are no meaningful
drawbacks.
e. They are the only real option for open water tec diving in a wet suit.

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Exercise, Other Delivery Content, Tec 45-1

1. Multigas computers have become the standard of practice in tec diving because (choose
all that apply)
q a. they handle multiple gases and CCR diving.
q b. they maximize your options in an emergency.
q c. their decompression models are newer than those in single gas computers.
q d. they are smaller than single gas computers.
2. DSMBs are replacing lift bags in many tec diving situations because (choose all that apply)
q a. they don’t stick so far up into the wind.
q b. they are more compact on your rig.
q c. they have no-spill designs.
q d. some have special inflation systems.
3. It is unlikely that a quick release on your harness shoulder would fail, but if it did, you
would only need to tie off the loose end.
q True
q False
4. Perhaps the most common weighting error in tec diving is
q a. under weighting.
q b. over weighting.
q c. neutral weighting.
q d. None of the above.
5. Backup buoyancy control is critical in open water, open circuit tec diving because if
you’re properly weighted and your primary BCD fails, you risk being unable to decom-
press adequately.
q True
q False
6. Problems with trying to use a lift bag or DSMB as a backup buoyancy system include
(choose all that apply)
q a. it is a complex skill with low reliability for use under stress after disuse.
q b. it is difficult to conduct that skill and other complex skills at the same time.
q c. hanging from a floating DSMB/lift bag may compromise the quality of decom-
pression.
q d. hanging from a floating DSMB/lift bag requires a heavier line/reel than tec divers
like to use.

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7. Several manufacturers endorse the use of the lift bags/DSMBs are emergency backup
buoyancy devices.
q True
q False
8. The redundant (double bladder) BCD is the most realistic approach to providing backup
buoyancy control because (choose all that apply)
q a. they were designed specifically for this purpose.
q b. you use them exactly like you use your primary BCD – a practiced skill.
q c. it is applicable to almost all dive environments.
q d. other than a slightly higher cost, it has no meaningful drawbacks.

How did you do?

1. a, b. 2. b, c, d. 3. True. 4. a. 5. True. 6. a, b, c, d. 7. False. 8. a, b, c, d.

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Other Delivery Content, Tec 45-2

Study assignment: Tec 45 Handout 2

Learning Objectives
By the end of this section, you should be able to answer this question:
1. Why may you set a multigas computer for gas blends you don’t plan to use on a dive?

L. More on using multigas computers in emergency situations

1. You do not have to use a gas just because you set your multigas dive com-
puter for it.
2. Dive computers that support a large number of gases can be set for gases
you don’t plan to use, but that would be available for use in an emergency.
This gives you more gas options in the event of an emergency.
a. Example: Deco gases used by another team that will be diving along
with your team may be different from your team’s, but available for
sharing.
b. Example: Air is readily available in many dive environments, so
support divers could bring it for decompression use if nothing else
were quickly obtainable.
3. The main drawback to having your multigas computer set for gases you
don’t plan to use is that you have to be sure you don’t select one of the con-
tingency gases by accident.
4. Some of the newest computers will allow you to enter a new gas during the
dive should you need to do so in an emergency situation. The computer can
then calculate your decompression accordingly.

Exercise, Other Delivery Content, Tec 45-2

1. You might set a multigas computer for gas blends you don’t plan to use during a dive so
your computer can calculate your decompression with them in an emergency situation.
q True
q False

How did you do?

1. True.

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Other Delivery Content, Tec 45-3

Study assignment: Tec 45 Handout 3

Learning Objectives
By the end of this section, you should be able to answer this question:
1. What are your two options for conducting deep stops?
2. What is the current thinking regarding deep stops?
3. What approach to deep stops seems to be the most prudent?

G. More on deep stops

1. There are two primary options for conducting deep stops.
a. The first is to use a conventional dissolved gas decompression model
and then add deep stops as discussed previously and in the Tec Deep
Diver Manual.
b. The second is to use a decompression model that inherently stops
you deeper than other models. Most “bubble” models fit into
this category.
2. Although deep stops had a lot of anecdotal support at one time, the current
thinking based on US Navy Experimental Diving Unit research is that they
may not be as beneficial as once thought.
a. The USN compared a bubble model and conventional dissolved gas
model on manned test dives. Dives were to the same depth for the
same duration with the same decompression time distributed over a
deep stops (bubble) schedule and a conventional (dissolved gas)
schedule.
b. The tests were terminated due to an unacceptable DCS rate in
subjects decompressed with the bubble schedule.
3. Other data are less conclusive.
a. Some no stop diving tests find a minor benefit to deep stops.
b. Many divers have been using bubble models without
difficulties.
c. Deep stops and bubble models are common practices widely used in
the tec community, again, without widespread
problems.

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4. The prudent approach to deep stops at the moment seems to be:

a. Use a conventional dissolved gas model and add deep
stops as you learned. The deep stops will lengthen your shallower
stops.
b. If you wish to use a decompression bubble model, choose one that is
well supported by human test data.
c. Whatever model you use, stay well within limits and pad your decom-
pression to make it conservative. Don’t be in a hurry to leave your last
stop – extend it beyond the required time.
d. Stay up to date on the latest findings in decompression research.
Know your sources – just because someone says something on an
internet forum doesn’t make it true.

Exercise, Other Delivery Content, Tec 45-3

1. Your two options for deep stops include (choose all that apply)
q a. using a deep stops bubble model.
q b. adding deep stops to a bubble model.
q c. using a conventional dissolved gas model.
q d. adding deep stops to a conventional dissolved gas model.
2. The current thinking on deep stops is
q a. they are unquestionably beneficial.
q b. they are unquestionably without benefit.
q c. there is some doubt about whether they’re as beneficial as once thought.
3. To use deep stops prudently (choose all that apply)
q a. use a conventional model, add deep stops and complete the extra deco they add.
q b. if you use a bubble model, use one well supported with human test data.
q c. use any model conservatively.
q d. stay informed about the latest findings in decompression theory.

How did you do?

1. a, d. 2. c. 3. a, b, c, d.

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Manual Supported Content
45 Knowledge
Study assignment: Tec Deep Diver Manual, pgs 173-175, Team Diving III, Tec
Exercise 3.5
Reviews
Tec Deep Diver
Digital Manual

Tec 45 Knowledge Review One

Appendix Instructor
Please complete this review to hand in to your instructor. If there’s something you Guide
don’t understand, review the related material. If you still don’t understand, be sure to have
your instructor explain it to you.
2. What are your responsibilities during the Tec 45 course?
1. What are the limits of your training as a Tec 45 diver?

Appendix Instructor Guide

2. What are your responsibilities during the Tec 45 course?

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3. What is meant by “standardized technical rig” and why do you need to apply it?

3. What is meant by “standardized technical rig” and why do you need to apply it?

4. Describe the proper types, number, location and configuration within your rig of
the following equipment components and how your gear will look when worn:

Manifold (if applicable) -

4. Describe the proper types, number, location and configuration within your rig of
the following equipment components and how your gear will look when worn:
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Manifold (if applicable) -
 Instructor Guide Appendix

Right regulator and accessories –

Sidemount –

Left regulator and accessories –

BCD and harness -

Instruments –

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 Appendix Instructor Guide

Compass –

Timing Device & Depth Gauge –

Cutting tools –

Pockets and clips -

5. Describe a suitably rigged stage/deco bottle.

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 Instructor Guide Appendix

6. List three reasons why tec divers consider a slate standard equipment.

7. List three types of dive computers you can use for technical diving with air and
enriched air, along with the advantages and disadvantages of each.

8. Name two buoyancy control devices and explain what is meant by “appropriate
back up buoyancy. ”

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 Appendix Instructor Guide

9. How does a technical dive in dry suit differ from a recreational dive? What is the
recommended number of recreational dives in a dry suit that you should have
before using it on a technical dive?

10. What are four different weighting options for tec diving and list the advantages
and disadvantages of each.

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 Instructor Guide Appendix

11. What is the primary hazard of diving negatively buoyant, and how do you manage
this hazard?

12. List the guidelines regarding material and equipment compatibility using enriched
air and oxygen. What do you risk if you fail to follow these guidelines?

13. List four reasons why DSMBs are replacing lift bags in tec diving situations.

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 Appendix Instructor Guide

14. (Metric) If your SAC rate is 24 litres/minute, how much gas volume do you need
for 20 minutes at 30 metres? What would your total volume be with a reserve
based on the rule of thirds?

14. (Imperial) If you SAC rate is . 8 cfm, how much gas volume do you need for 20
minutes at 90 feet?

15. (Metric) What is your turn pressure for your back gas based on the dive profile
information below? Do you have enough back gas to do the dive and return with a
one-third reserve?

15. (Imperial) What is your turn pressure for your back gas based on the dive profile
information below? Do you have enough back gas to do the dive and return with a
one-third reserve?

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 Instructor Guide Appendix

16. Explain how you determine your required decompression stops using a single gas
computer or table, and how to use switches to enriched air or oxygen to make the
decompression more conservative.

17. What is a gas-switch, extended no-stop dive?

18. What should you do if you find narcosis affecting your or your team mate’s ability
to accomplish the mission and/or dive safely?

19. What is your END with enriched air and why?

20. What is the “ideal” oxygen in a gas mix for a dive to 25 metres/83 feet?

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 Appendix Instructor Guide

21. List your responsibilities as a team member when technical diving.

22. Where is your team mates rank in your chain of back ups? What is the one back up your
team mates provide that you cannot provide?

23. What are four guidelines to consider when planning to tec dive in an unfamiliar
environment?

24. What is the myth about learning to dive with certain methodologies or in certain
environments?

Student Diver statement: I’ve reviewed the questions I answered incorrectly or incompletely
and I now understand what I missed.

Signature _________________________________________ Date ________________

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 Instructor Guide Appendix

Tec 45 Knowledge Development Two

Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 176-179, Thinking Like a
Tec Diver III, Tec Exercise 3.6
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 194-201, Gas Planning IV,
Tec Exercise 4.2
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 202-209, Emergencies IV,
Tec Exercise 4.3
Other Delivery Content, Tec 45-2
Study assignment: Tec 45 Handout 2

Tec 45 Knowledge Review Two

Please complete this review to hand in to your instructor. If there’s something you
don’t understand, review the related material. If you still don’t understand, be sure to have
your instructor explain it to you.

1. Define a “trust me dive” and explain why you should not make them.

2. List the six principals for surviving a tec dive.

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 3. What is run time? How do you use it?

4. Explain what you should do if you cannot switch to your shallower gas blend when
making a gas switch extended no-stop dive.

5. Gas matching (optional): You are diving double 18 litre/104 cubic foot (working
pressure 2400) cylinders filled to 150 bar/2200 psi. Your team mate will use double
21 litre/120 cubic foot (working pressure 2400) cylinders filled to 160 bar/2350 psi.
If you gas match, what pressure should you have remaining at the end of the dive,
and at what pressure should you turn the dive?

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 6. What should you do to ensure you don’t lose your decompression cylinders?

Appendix Instructor Guide

7. What do you do if your dive goes deeper and/or longer than planned?

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8. What should you do if you miss a decompression stop?

9. What should you do if you have a delay in your ascent to a decompression stop?

10. What should you do if you omit some or all of your decompression?

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 Instructor Guide Appendix

11. What should you do if you run out of gas?

12. How do you handle a lift bag that spills as it ascends be cannot be pulled back down
to be redeployed?

13. What is a drift kit? What items would you have in it, and when would you use it?

Student Diver statement: I’ve reviewed the questions I answered incorrectly or incompletely
and I now understand what I missed.

Signature _________________________________________ Date ________________

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 Instructor Guide Appendix

Tec 45 Knowledge Development Three

Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 192-194, Equipment IV, Tec
Exercise 4.1
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 210-211, Thinking Like a Tec
Diver IV, Tec Exercise 4.4
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 222-227, Oxygen Window and
Accelerated Decompression, Deep Stops, Tec Exercise 5.1
Other Delivery Content, Tec 45-3
Study assignment: Tec 45 Handout 3
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs 228-229, Techniques IV, Tec
Exercise 5.2

Tec 45 Knowledge Review Three

Please complete this review to hand in to your instructor. If there’s something you
don’t understand, review the related material. If you still don’t understand, be sure to have
your instructor explain it to you.

1. Explain the difference and give examples of acceptable and unacceptable home-
made gear. What is the most common homemade item used by tec divers?

2. List four attitudes that characterize leading tec divers.

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 3. What is the oxygen window?

4. List three techniques you can use to make accelerated deco dives more conservative.

5. What are two primary options for conducting deep stops?

6. Define a “drift hang,” and list four disadvantages of using it.

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 7. What is the most important resource in a tec diving emergency and what provides
this resource?

8. What is an air break and how is it performed?

Student Diver statement: I’ve reviewed the questions I answered incorrectly or incompletely
and I now understand what I missed.

Signature _________________________________________ Date ________________

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 Tec Deep Diver
Digital Manual

50

Independent
Study
Assignments

Chapter 6

Handouts

Knowledge
Reviews

Appendix

Main Menu

Tec 50 » Chapter Six

 Instructor Guide 50 Tec Deep Diver
Digital Manual
Independent
Appendix
Study Assignments
Tec 50
Tec 50 Knowledge Development One
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pg 230, Equipment V,
Tec Exercise 5.3
Other Delivery Content, Tec 50-1
Study assignment: Tec 50 Handout 1
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pg 231-232, Thinking Like a
Tec Diver V, Tec Exercise 5.4.
Other Delivery Content, Tec 50-2
Study assignment: Tec 50 Handout 2
Manual Supported Content
Study assignment: Tec Deep Diver Manual, pg 233-235, Mission Planning,
Tec Exercise 5.5.

Tec 50 Knowledge Review One

Please complete this review to hand in to your instructor. If there’s something you
don’t understand, review the related material. If you still don’t understand, be sure to have
your instructor explain it to you.

1. What are the limits of your training as a Tec 50 diver?

2. What is the priority and how do you respond to an unresponsive diver at depth
during a decompression dive?

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 Decompression in any form, was, is,

and will always be, a necessary pain in

the [rear end].

Bob Barth, The Sea Dwellers, 1999
US Navy Diver, Aquanaut,
Sealabs I, II & III

Chapter SIX: The Polish

C
hapter Six — last but not least. Well, it is least
in that it’s the shortest. Chapter Six puts the
final polish on the knowledge you’ve been
developing and applying in this course. You
start with emergencies and a detailed review of
decompression illness and its first aid. Then, thinking like a
tec diver goes into some final thoughts and advice for you,
SIX
the soon-to-be Tec Deep Diver.
And that’s it. After you master the Tec Objectives in this
chapter, you should be ready for the final two practical
applications (including the second exam), and for your
final three training dives.

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 Tec Objectives Emergencies VI
If there’s anything you’ve picked up in this course,
Highlight or underline the it’s that technical divers face risks that recreational
answers to these questions divers don’t, and face some of the same risks to a
as you find them: greater degree. One of the latter is decompression ill-
1. How do you define ness (DCI). This is an issue important enough that
decompression sickness, it’s worth reviewing what you’ve already learned
arterial gas embolism and about DCI.
decompression illness?
As you learned in the PADI Rescue Diver course, arte-
2. What are the signs and
symptoms of decompres- rial gas embolism (AGE) is the condition in which air
sion illness? bubbles enter the bloodstream through a lung rup-
ture, usually the result of holding the breath during
3. What is the first aid for
suspected decompression ascent. Decompression sickness (DCS) is the condition
illness? in which inert gas (nitrogen) forms bubbles in the tis-
sues and bloodstream as it comes out of solution due
4. How does administering
oxygen benefit a patient to high supersaturation following ascent.
with decompression ill-
Decompression illness is the field term for both DCS
ness?
and AGE together. The first aid and emergency man-
5. How do you administer a agement for both is identical, so it’s not important —
field neurological exam?
and sometimes impossible — to distinguish between
6. How can having diver DCS and AGE. In a first aid situation, you only need
accident insurance make think about the one, broader condition — DCI.
treatment for decompres-
sion illness more effective? Signs and symptoms of DCI include pain in the
joints or mid limb, undue fatigue, inability to uri-
nate, blurred vision, blotchy skin rash, tingling in
the extremities, swelling, vertigo, hearing or speech impairment,
paralysis, numbness, unconsciousness, bloody froth from the
mouth, loss of coordination, personality change and respiratory/
cardiac arrest. The symptoms can be immediate (usually when AGE
related), or delayed (when DCS related).

First Aid for DCI

At this writing, the recommendations for DCI first aid are as follows,
but it’s your responsibility to keep up with the latest findings on
DCI first aid, and follow the most up to date protocols. It’s also your
responsibility to include preparing to handle DCI in dive planning,
including both first aid and steps for getting a patient into emer-
gency medical care.
• Keep the patient lying down; on the back is fine for a responsive
patient, left side down (recovery position) is the position to use
for an unresponsive breathing patient.

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 • Monitor airway, breathing and cir-
culation (ABCs) and administer CPR
as necessary.
• Administer emergency oxygen to a
breathing patient, ideally 100 per-
cent via a demand system.
A very weak patient may not be
able to breathe with a demand sys-
tem — use freeflow oxygen with a
nonrebreather mask and reservoir
bag set at 15 litres per minute flow
The primary first aid for suspected DCI is to administer emer-
rate. Remember to inflate the bag gency oxygen to a breathing patient, ideally 100 percent via
before placing the mask on the a demand system.
patient’s face; if the bag deflates
completely when the patient
inhales, set the flow at 25 litres per minute.
For a nonbreathing patient, use freeflow oxygen while provid-
ing rescue breaths through a pocket mask. If the patient resumes
breathing, switch to the demand or nonrebreather mask.
Continue oxygen until you get the patient into emergency
medical care, or until you run out.
Monitor the oxygen pressure gauge;
don’t let the cylinder run empty
with the mask still on the patient.
If you run out of oxygen, as a tec
diver you may have EANx80 or
other high oxygen blend to use if
the patient can breathe through a
standard regulator.
You may give a fully responsive
patient fluids to help maintain
hydration. Keep the patient lying A very weak patient may not be able to breathe with a
down, with water the preferred demand system — use freeflow oxygen with a nonrebreather
fluid. Isotonic fluids and fruit juices mask and reservoir bag set at 15 litres per minute flow rate.

are acceptable; avoid anything with

caffeine or alcohol.
SIX
• Contact emergency medical care and the diver emergency ser-
vice (DAN, DES) that serves the area and get the patient into
emergency medical care, and ultimately to a recompression
facility as guided by the diver emergency service and the local
medical system. Statistics show that the sooner recompression

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 treatment begins, the more probable is complete
resolution of symptoms. Delays, on the other hand,
are more prone to leave permanent or extended
residual symptoms.

The Importance of Oxygen

After all you’ve learned about oxygen’s role in
decompression, it’s logical that it can play a big
part in managing DCI. Oxygen administration
has proved to reduce DCI symptom severity and
improve the probability of a successful treatment.
Sometimes, symptoms disappear entirely while the
patient is on oxygen (though it doesn’t usually
replace recompression therapy).
Once DCI manifests itself, breathing pure oxygen
helps oxygenate tissues suffering from restricted
blood flow due to bubble formation. This helps
For a nonbreathing patient, use freeflow oxy- protect these tissues until the patient receives
gen while providing rescue breaths through a
pocket mask. recompression, and is a benefit that has little rela-
tionship to the benefits of breathing oxygen while
decompressing.
On the other hand, just as it does in decompression, the oxygen
window speeds dissolved nitrogen out of the body faster, minimiz-
ing and slowing further bubble growth to reduce further and wors-
ening symptoms. The longer you keep the oxygen window open,
the better.
Plan your emergency
oxygen supply based on
how long it would take
to get a diver into emer-
gency medical care. You
can extend your oxy-
gen supply by adding a
rebreather emergency
oxygen unit to your
emergency oxygen kit.
This unit recycles unused
oxygen and greatly
expands how long your
You can extend your oxygen supply by adding a rebreather emer-
supply lasts, though it gency oxygen unit to your emergency oxygen kit. This unit recycles
takes a little bit of addi- unused oxygen and greatly expands how long your supply lasts,
tional training to use. though it takes a little bit of additional training to use.

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 Field Neurological Examination
DCI symptoms and signs can be ambiguous. If unsure whether symp-
toms suggest DCI, you can use a field neurological exam to look for pos-
sible effects on the nervous system. If you find any irregularities, assume
DCI, begin first aid and contact emergency medical care.
To perform a field neurological exam:
1. Have the patient follow your finger with both eyes. They should track
together.
2. Have the patient use both hands to squeeze yours. Weakness on one
side suggests a problem.
3. Ask the patient to close both eyes, stretch out the arms and then bend
at the elbows to touch the nose with fingertips. The inability to do this
with both or either hand suggests a problem.
4. The patient should be able to stand on one foot.
5. Snap your fingers on either side of the patient’s head. Ask if there’s
any significant difference in loudness. A significant difference can sug-
gest nerve damage, though with this test ear squeeze or water in the
ear canal could be at fault. Obviously, a field examination by a lay
rescuer isn’t intended to replace diagnosis by emergency medical pro-
fessionals.

The Role of Diver Accident Insurance

Besides emergency oxygen and recompression, one of the best tools for a
more effective DCI treatment is diver accident insurance. At first it might
not seem that helping pay for treatment should make the treatment any
better, but it can.
Because the more quickly a patient begins treatment the more likely a
favorable outcome, you want to minimize anything that would delay
treatment should you ever need it — especially as a tec diver. Delays
sometimes result from questions about payment for a recompression
treatment, especially because most conventional medical policies do not
cover recompression. Diver accident insurance minimizes these delays by
establishing the financial coverage. This is why some dive charter boats
and dive sites, especially those catering to tec divers, require diver acci-
dent insurance.
SIX
Therefore, carrying diver accident insurance that covers tec diving (be
sure it’s stipulated in the coverage you get) such as offered by PADI and
DAN, reduces or eliminates recompression delays that would stem from
financial concerns. Compared to your overall investment in tec diving,
diver accident insurance costs very little, yet can potentially benefit treat-
ment outcome and the financial picture if you should experience DCI.

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 The truth is, given the higher risks you face as a tec diver, you’re
not being very responsible if you don’t carry diver accident insur-
ance coverage.

Tec Exercise – 6.1

1. Decompression illness (check all that apply): 4. Administering oxygen benefits a patient by oxygenating
a. may be caused by inert nitrogen coming out of tissues with restricted blood flow, and by helping speed
solution in the tissues. dissolved nitrogen out of the tissues.
True False
b. may be caused by air entering the bloodstream
through a lung rupture. 5. Steps in administering a field neurological exam include
c. exactly the same thing as DCS. (check all that apply):
d. is a term used in the field for both DCS and AGE. a. having the patient follow your finger with both
eyes.
2. Signs and symptoms of DCI include (check all that apply): b. having the patient squeeze your hands.
a. pain in the joints/mid limb
c. having the patient listen for your fingers to snap on
b. paralysis either side of the head.
c. unconsciousness d. having the patient jump up and down on one foot
d. undue fatigue with the eyes closed.

3. The first aid for a suspected DCI patient includes (check 6. Diver accident insurance benefits recompression treat-
all that apply): ment by allowing you to afford therapies that are expen-
sive and considered optional.
a. 100 percent oxygen.
True False.
b. keep the patient seated.
c. CPR and rescue breathing as needed.
d. contact emergency medical care and the local diver
emergency service.

Check it out:
1. a,b,d. 2.a,b,c,d. 3. a,c,d. b is incorrect because the patient should be kept lying down. 4. True. 5. a,b,c. 6. False. Diver
accident insurance benefits recompression by reducing delays associated with questions about payment.

Tec Objectives Thinking Like a Tec Diver VI

The Tec Deep Diver course qualifies you to enter the
Highlight or underline the initial ranks of deep tec diving. Hopefully, the one
answers to these questions thing you’ve learned as you’ve gone through your
as you find them:
training is that there’s quite a difference between
1. How do prudent tec div- knowing what a tec dive requires and doing the
ers broaden their abilities dive. The difference lies in the gap between theory
and limits within tec div-
and practice, between going through the steps to a
ing?
procedure for a first run, and enacting the same pro-
2. What quality do you find cedure automatically when you or a team mate’s life
in tec divers who extend
depends on it. You only get where you need to be
their personal limits at an
appropriate pace? through practice and experience.

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 Consider that when astronauts and cosmonauts train, they may
train for three or four years for a single mission. They practice the
procedures for every conceivable emergency, ranging from minor
equipment failure to having their space craft begin to disintegrate
around them as they launch. Many of the procedures are simple to
describe — but not so simple to apply amid a thousand other tasks
they have to manage. Space travel makes it clear that knowing and
doing are two things, and the training has to reflect that. No one
goes into space until entirely trained and qualified. The stakes are
(Photo courtesy of NASA)
way too high.
“Sure, but that’s for space,” you might say, “Tec div-
ing doesn’t take all that.”
Astronauts and cosmonauts do train for a more
demanding environment using far more complex
technology, but they and tec divers face similar chal-
lenges, albeit on different complexity scales. Both
enter an extreme environment where humans cannot
live without life support. Both do so in a manner in
which they depend utterly on that life support. Both
go where there’s no rescue possible (most of the time,
anyway).
The quantity of knowledge and number of skills need- Astronauts and cosmonauts, and tec
ed for space travel far surpasses tec diving, but the divers face similar challenges, albeit on
required mastery level and the psychological stresses different complexity scales. Both enter
an extreme environment where humans
are surprisingly similar. And, an astronaut crew has
cannot live without life support. Both do
an advantage over a tec dive team — when there’s a so in a manner in which they depend
problem, the crew has more than a thousand experts utterly on that life support. Both go
from every field on the ground standing by to create where there’s no rescue possible.

a solution and talk them through it. When you face

a problem in tec diving, your team faces it alone.
With these similarities, it should be no surprise to learn that the Tec
Deep Diver course and astronaut/cosmonaut training have paral-
lels, and in fact in many ways this course draws directly upon what
the US National Aeronautics and Space Administration (NASA) has
learned in almost four decades of training humans for space flight.
What’s the point of all this? Simple: Even before they finish the
course, it’s not unusual for many divers entering tec diving to be
SIX
thinking ahead to their next course and extending beyond the lim-
its this course qualifies them for. But getting ahead of yourself in
tec diving is the recipe for getting hurt or killed — you may know
the theories, you may be able to explain an emergency proce-
dure, but in tec diving as in space travel, there’s often a huge gap
between knowing and doing.

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 Here’s how prudent tec divers (which includes you, right?) expand
their abilities:
Gain Experience. The most important immediate step is to gain
experience within your current qualifications. Experience now
forms the foundation you need to build on to go forward. The Tec
Deep Diver course develops skills that you’ll need to enact innately
during more complex dives. Dive, dive, dive and make these skills
as routine as your recreational dive skills are.
Push Your Comfort Zone Gently. It’s acceptable to extend your
limits a bit as you gain experience — if it weren’t, there would be
no way to grow. Prudent tec divers extend themselves
carefully, only slightly beyond their experience, and are
always prepared to pull back.
Learn From Those With Experience. Hang out with
and dive with experienced tec divers, especially teams.
You’ll learn a lot and get a lot of guidance. Although
you typically start as a support diver, as you prove your
mettle, gain experience and broaden your qualifications,
you’ll find yourself on increasingly exciting dives.
Respect the Limits. Although you’re extending your lim-
its, you’ve been taught the outside limits to your quali-
fications. Respect these. They’re the line between where
experience ends and training has to pick up for you to
move on without unreasonable risk.

Keep in mind that the top names Continue Training. In some types of tec diving, such as
cave diving or inside wrecks, learning by experience is
and leaders in tec diving, almost as
a rule, reached their current status
extremely hazardous. The way to move past the outside
over a period of years and hundreds
of dives and by sharing a common
limits to your qualifications, once you’ve gained experi-
quality: patience. ence, is to train for a new set of limits and gain experi-
ence with them. Yes, before there was training others
had to go through the limits without it, but that’s done. No need to
repeat their mistakes (some of which killed people).
Keep in mind that the top names and leaders in tec diving, almost
as a rule, reached their current status over a period of years and
hundreds of dives. Some grew faster than others, depending on
their aptitude and the state of the art at the time, but they came to
the forefront of tec diving by sharing a common quality: patience.
They didn’t move on before they were prepared and qualified. To
be blunt, if you don’t have patience, you don’t belong in tec diving.
If you do, best of success to you and the teams you work with.

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 Tec Exercise – 6.1

1. Prudent tec divers expand their limits by (check all that 2. The quality tec divers who extend their limits prudent
apply): share is ___________.
a. gaining experience.
b. pushing their comfort zone gently.
c. learning from those with experience.
Check it out:
d. respecting the limits of their training. 1. a,b,c,d. 2. patience.

Performance
Preview:
Objectives Practical Application Seven
To successfully complete this
During this practical application, you’ll work in
Practical Application, you teams to plan Training Dives Ten and Eleven
will be able to: based on information your instructor provides.
1. Working as a team, plan
By now, complete dive planning should be
Training Dives Ten and becoming routine for you. Consider A Good
Eleven following the Diver’s Main Objective Is To Live and refer
A Good Diver’s Main back to this manual as you plan. Dive Ten is a
Objective Is To Live pro- decompression dive based on a single gas table/
cedure, including mission
computer, with at least two decompression stops
planning, based on the
dive specifics (depths, envi- using enriched air and/or oxygen to make the
ronment, etc.) and mission decompression more conservative. Dive Eleven is
provided by the instructor. an accelerated decompression dive with at least
two decompression stops.
Both dives will also have a mission component
that your instructor will assign. Your dive plan should include how
you will attempt to accomplish this mission. Note: As before, since
the mission is your last priority, you do not necessarily have to
complete the mission. If you’re unable to complete the task, your
instructor will consider how effective you and your team were amid
the other dive requirements. Accomplishing as much as would be
reasonably possible without violating safety guidelines or the dive
plan is what your instructor will be interested in.
Your instructor will provide the basis for determining your deco
SIX
schedule and have you calculate, OTUs and CNS for each diver and
gas, plus gas requirements including one-third reserve, tank base
lines, turn points, equipment requirements, logistics, emergency
procedures and other information from the A Good Diver’s Main
Objective Is To Live planning process.

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 Your written plans should contain all information you would need
to make the dives.

Preview: Training Dive Ten

Performance Objectives

To successfully complete this training dive, To Live procedure, and perform predive
you will be able to: checks following the Being Wary Reduces
All Failures procedure, the bubble checks
1. Working in a team, plan and execute a
and descent checks.
decompression dive based on a single
gas table or computer with an enriched 2. Working in a team execute the dive’s
air blend for added conservatism follow- mission, carrying it out to the team’s
ing the A Good Diver’s Main Objective Is ability within the limits of the dive plan.

Predive briefing and gearing up

Training Dive Ten

Entry — appropriate for environment
Weight check (if needed)
Bubble check
Don stage/deco cylinders at surface
Descent
Descent check
Mission
Ascent — NO TOX switches and decompression — air breaks
Surface — remove stage/deco cylinders at surface
Exit

Post Dive
Performance review
Disassemble and stow equipment
Log dive for instructor signature.

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 Preview: Training Dive Eleven Performance
Training Dive Eleven Objectives
Entry — appropriate for environment To successfully complete this
training dive, you will be able to:
Weight check (if needed)
1. Working in a team, plan and
Bubble check execute an accelerated decom-
Don stage/deco cylinders at surface pression dive based on table
and/or multigas computer fol-
Descent lowing the A Good Diver’s Main
Objective Is To Live procedure,
Descent check and perform predive checks fol-
lowing the Being Wary Reduces
Mission
All Failures procedure, the bub-
Ascent — NO TOX switches and decompression ble checks and descent checks.
— air breaks 2. Working in a team execute the
dive’s mission, carrying it out
Surface — remove stage/deco cylinders at sur- to the team’s ability within the
face limits of the dive plan.
Exit

Post Dive
Performance review
Disassemble and stow equipment
Log dive for instructor signature.

Performance
Preview:
Objectives Practical Application Eight
To successfully complete this During this practical application, you’ll work in
Practical Application, you teams to plan Training Dive Twelve based on
will be able to: information your instructor provides. Dive plan-
1. Working as a team, plan ning should be becoming routine for you. Your
Training Dive Twelve fol- written plan should contain all information you
lowing the A Good Diver’s would need to make the dive.
Main Objective Is To Live
procedure, including mis- You will also complete Exam Two. As with Exam
One, this is not a team exercise. You may use a
SIX
sion planning, based on
the dive specifics (depths, calculator, and refer to the tables in the appen-
environment, etc.) and dix of this manual, but no other section. As with
mission provided by the
Exam One, you’ll be required to hand in your
instructor.
scatch paper. You must earn 80 percent or better
on both sections to be successful.

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 Preview: Training Dive Twelve

Performance Objectives

To successfully complete this training dive, form predive checks following the Being
you will be able to: Wary Reduces All Failures procedure, the
bubble checks and descent checks.
1. Working in a team, plan and execute
a two or more stop decompression 2. Working in a team execute the dive’s
dive based on table and/or a com- mission, carrying it out to the team’s
puter following the A Good Diver’s Main ability within the limits of the dive plan.
Objective Is To Live procedure, and per-

Training Dive Twelve

Entry — appropriate for environment
Weight check (if needed)
Bubble check
Don stage/deco cylinders at surface
Descent
Descent check
Mission
Ascent — NO TOX switches and decompression — air breaks
Surface — remove stage/deco cylinders at surface
Exit

Post Dive
Performance review
Disassemble and stow equipment
Log dive for instructor signature.

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 Instructor Guide 50 Handouts Tec Deep Diver
Digital Manual

Appendix

Tec 50
Other Delivery Content, Tec 50-1
Study assignment: Tec 50 Handout 1

Learning Objectives
By the end of this section, you should be able to answer this question:
1. What are the options and considerations for long hose gas sharing during the decom-
pression phase of a technical dive?

D. Sharing gas with the long hose is usually a procedure that closes the gap between
when the victim loses the gas supply and reaches another independent gas supply or
the surface.
1. On a deco dive, if there are stops before the first gas switch, it may be nec-
essary to supply gas to the affected diver on those stops.
2. One advantage of a three person team is that it provides two people to help
the one – both divers can provide gas to the victim at various intervals so
that neither one has a severely depleted supply.
3. At the first gas switch, the victim can usually dive independently through
the rest of the dive.
a. At the Tec 50 level, air breaks will not usually be needed until after
the second gas switch; the affected diver can usually break on the
lower oxygen deco gas.
b. If the first deco gas is EANx50 or higher, however, the diver may
need to share gas for air breaks.
c. At the surface after completing decompression, the victim will usual-
ly breathe from a deco cylinder while orally inflating the BCD, but
it’s a good idea for a team mate to stay ready with the long hose until
the victim is out of the water.

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Exercise, Other Delivery Content, Tec 50-1

1. Considerations and options for long hose gas sharing on a decompression dive include
(choose all that apply):
q a. the depth at which the victim switches to the first deco gas.
q b. whether the victim will need long hose gas sharing for air breaks.
q c. whether the long hose is oxygen compatible.
q d. being ready to provide assistance at the surface after completing
decompression.

How did you do?

a, b, d.

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Other Delivery Content, Tec 50-2

Study assignment: Tec 50 Handout 2

Learning Objectives
By the end of this section, you should be able to answer this question:
1. What are three reasons you may want to “tec dive” in a pool or shallow water?

C. Practice, practice, practice

1. Tec diving involves a lot of motor procedures. A motor procedure is a series
of motor skills that you carry out in sequence in response to a need of some
kind (routine or emergency).
2. Motor skills erode with disuse, but usually refresh quickly with practice.
3. New situations may call for creating new motor procedures.
4. As a tec diver, you may find it a good idea to practice your tec diving skills
in a pool or other shallow, no stop dive situation for these reasons:
a. To refresh your skills – You already know you need to do this as a
recreational diver if you’ve not been active in awhile. Even if you’re
active as a tec diver, however, you may want to refresh seldom-used
emergency skills. These may include long hose drills, send up lift
bags/DSMBs, drift decompression, etc. – whatever skills you may
need in an emergency, but have not actually practiced in quite a few
dives.
b. To extend your skills – You may need to apply what already know in
a new situation; practicing first may help. For example, if you may
have to don and remove deco cylinders in reduced visibility and
heavy surface chop while hanging onto a current line, it may be
worth practicing doing this with your face entirely underwater and
your eyes closed, while hanging onto a line.
c. To invent mission specific skills – Your dive plan may call for doing
something highly specific, such as recovering a lost object. If you
don’t know the best way to rig the object for recovery, you may want
to invent the procedure using a duplicate of it in shallow water.

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Exercise, Other Delivery Content, Tec 50-2

1. Reasons you may want to “tec dive” in a pool or shallow water include (choose all that
apply):
q a. refreshing your skills.
q b. teaching yourself to cave dive.
q c. to extend your skills to specific situations.
q d. to invent mission specific skills.

How did you do?

a, c, d.

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 Instructor Guide Appendix

Other Delivery Content, Tec 50-3

Study assignment: Tec 50 Handout 3

Learning Objectives
By the end of this section, you should be able to answer these questions:
1. What is trimix?
2. What are the advantages and disadvantages of diving with trimix?
3. What will your qualifications be with respect to diving with trimix as a Tec 50 diver?

A. At depths beyond 30 metres/100 feet, trimix is increasingly advantageous.

1. Trimix is a blend of oxygen, helium and nitrogen.
a. Much as enriched air nitrox is abbreviated “EANx,” trimix is abbre-
viated “TMx.”
b. Trimix nomenclature is to label a blend with the oxygen and helium
content. Example: TMx10.5/50 is 10.5 percent oxygen, 50 percent
helium, balance nitrogen
2. The prevailing view is that you use trimix for open water dives deeper than
50 metres/165 feet .
a. Deeper than 40 metres/130 feet, the prevailing view is that trimix is
required for overhead environments or complex open water environ-
ments.
b. Although using air as deep as 50 metres/165 feet for open water div-
ing has a long-standing record of being acceptable, the trend is
toward using trimix beginning at shallower depths.
c. However, air/EANx remains a viable option in the 30 metre/100 foot
to 50 metre/165 foot range in open water and reasonable conditions.

B. Advantages and disadvantages of trimix

1. Advantages
a. Reduced narcosis – Helium is not narcotic, so trimix greatly reduces
narcosis. This is particularly important for dives below 50
metres/165 feet, but is useful as shallow as 30 metres/100 feet for
complex dives, dealing with poor conditions. It is considered manda-
tory for overhead environment diving beyond 40 metres/130 feet.

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b. Reduced gas density – Helium is a lighter than oxygen and nitrogen

so it is easier to breathe under pressure. This reduction in respiratory
load is thought to help reduce carbon dioxide buildup by improving
respiratory exchange, as well by reducing the muscular effort
required to breathe.
c. Reduced oxygen exposure – At depths below 50 metres/165 feet, it
becomes increasingly important to reduce the oxygen in a breathing
gas. Helium is a better choice than nitrogen for reducing the fraction
of oxygen for both its non narcotic and its low gas density proper-
ties.
2. Disadvantages
a. Decompression times and schedules – Because helium diffuses more
rapidly than nitrogen, you need to use tables or mixed gas dive com-
puters set for the specific trimix you’re using.
• All else being equal, within typical tec diving limits, a trimix
dive requires more decompression than an air/EANx dive.
• You cannot simply use an air or EANx schedule for trimix,
even if the oxygen content is the same.
• Trimix almost always requires accelerated decompression
with higher oxygen deco gases.
• Most software and many high end tec diving computers sup-
port trimix, so planning your dives does not differ much from
what you do as a Tec 50 diver – but you must plan
for helium.
b. Theoretical DCS risk – Because helium diffuses rapidly, in theory
DCS is more likely with helium, particularly following a rapid
ascent, a poorly executed or omitted decompression stop, or similar
error.
• Recent examination of data does not find that this is clearly
the case. There may be more risk of DCS Type II (neurologi-
cal), though this isn’t clearly the case either.
• Some argue that helium’s rapid diffusion makes it more effi-
cient during decompression.

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 Instructor Guide Appendix

• Until we know more, the prudent practice is to assume it has

less error tolerance and higher risk; tight, well executed dive
skills and conservative schedules are part of reducing DCS
risk regardless of what gases you’re using.
• Although there is some question whether the helium diving
has a higher DCS risk, until we know more it is a risk you
must accept if you dive trimix.
c. Cost and availability – Helium is expensive, and in some areas, near-
ly impossible to get.
• Using open circuit scuba, the cost of helium can be significant.
• In some areas, helium isn’t available even at a high price.
• For this reason, in some areas trimix isn’t commonly used, or
used less frequently, for open water dives in the 30 metre/100 foot to
50 metre/165 foot range.
d. Heat loss – Helium absorbs heat rapidly and insulates poorly com-
pared to nitrogen-oxygen. For that reason (among others), you can-
not use it in a dry suit. The most common solution is to use a small
cylinder with an inflation gas (typically argon) to inflate the dry suit.
3. Note: Using trimix does not make an unsafe dive safe!
a. Trimix helps offset some of the disadvantages of air/EANx in deep
diving, but it does not eliminate risk.
b. Using trimix does not make it acceptable to dive in poor conditions
or situations beyond your experience and skill level. If the site is
unsafe for diving with air within air depth limits, pick another site
regardless of what gases you’re using.

C. Trimix and the Tec 50 certification

1. If your instructor is a DSAT Tec Trimix instructor, you may have the option
of using trimix on Tec 50 Training Dive Four.
2. Realize that this does not certify you or qualify you to dive trimix indepen-
dently.
3. To dive trimix, continue your training with the Tec Trimix 65 course and/or
the Tec Trimix Diver course.

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Exercise, Other Delivery Content, Tec 50-3

1. Trimix is a blend of oxygen, helium and nitrogen.
q True
q False
2. Advantages of diving with trimix include (choose all that apply):
q a. reduced narcosis.
q b. that it is a better insulator in your dry suit.
q c. it has less density.
q d. reduced oxygen exposure
3. Disadvantages of diving with trimix include (choose all that apply):
q a. theoretical DCS risk.
q b. cost and availability.
q c. longer decompression times.
q d. oxygen toxicity.

How did you do?

1. True. 2. a, c, d. 3. a, b, c.

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 50 Knowledge Tec Deep Diver
Manual Supported Content
Digital Manual
Study assignment: Tec Deep Diver Manual, pg 233-235, Mission Planning,
Tec Exercise 5.5.
Reviews
Tec 50 Knowledge Review One
Please complete this review to hand in to your instructor. If there’s something you
don’t understand, review the related material. If you still don’t understand, be sure to have
your instructor explain it to you.

1. What are the limits of your training as a Tec 50 diver?

2. What is the priority and how do you respond to an unresponsive diver at depth
during a decompression dive?

Appendix Instructor Guide

3. In what situation could long hose gas sharing be necessary in the decompression
phase of a technical dive? PADI
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4. Professionals involved with rescue sometimes cite the philosophy “Better thee than
me.” What does this mean and how does it apply to tec diving?

5. How do you plan for “specific” mistakes and emergencies?

6. What are three reasons may you want to “tec dive” in a pool or shallow water?

Tec 50 » Knowledge Main Menu Tec 50 Menu Tec 50 Handouts Tec 50 Independent Study Assignments 50KR-1
Reviews
 5. How do you plan for “specific” mistakes and emergencies?

6. What are three reasons may you want to “tec dive” in a pool or shallow water?

Instructor Guide Appendix

7. What is the most common mistake in mission planning? Where does mission planning
rank with the other aspects of a tec dive?

8. For a presentation that you are going to give to local biologists on invertebrate pop-
ulations on a local reef that about 2 kilometers/1 mile long, you are interested in
estimating the number of sea stars per square metre/yard at depths between 30
meters/100 feet and 42 meters/140 feet. Your team plans to get this number; what
subtasks might this mission entail? Would it be reasonable to do this in a single
dive? How many dives might it take assuming a single team of three divers?
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and I now understand what I missed.

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 Instructor Guide Appendix

Tec 50 Knowledge Development Two

Manual Supported Content
Study assignment: Tec Deep Diver Manual, pgs245-252, Chapter Six, all
Tec Exercises.
Other Delivery Content, Tec 50-3
Study assignment: Tec 50 Handout 3

Tec 50 Knowledge Review Two

Please complete this review to hand in to your instructor. If there’s something you don’t
understand, review the related material. If you still don’t understand, be sure to have your
instructor explain it to you.

1. Define decompression sickness, arterial gas embolism and decompression illness:

2. List the signs and symptoms of decompression illness.

3. Explain the procedure for first aid for suspected decompression illness.

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 4. Explain how to administer a field neurological exam.

5. Explain how having diver accident insurance can make treatment for decompres-
sion illness more effective.

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 Instructor Guide Appendix

6. How does administering oxygen benefit a patient with decompression illness?

7. List the steps you will take as a prudent tec diver to broaden your abilities and lim-
its within tec diving.

8. What quality should you have to extend your personal limits at an appropriate pace?

9. What is trimix?

10. What are the advantages and disadvantages of diving with trimix?

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 Appendix Instructor Guide

11. What will your qualifications be with respect to diving with trimix as a
Tec 50 diver?

12. (Metric) You plan a dive to 44 metres using a single gas enriched air computer set
for EANx26. You plan to decompress using EANx80 from 9 metres to the surface.
You estimate that your bottom time will be 40 minutes. Your dive tables for
EANx26 show that 40 minutes at 44 metres requires 3 minutes decompression at
12 metres, 10 at 9 metres, 17 at 6 metres and 43 at 3 metres. Your ascent rate is 10
mpm. Your SAC rate is 19 litres per minute on the working part of the dive, and
16 lpm (litres per minute) when decompressing.

• Following the rule of thirds, how much of each gas do you need for this dive?

• If you have twin 18 litre cylinders with 170 bar of EANx26 do you have enough
EANx26 for the dive? If you have a 13 litre cylinder with 205 bar of EANx80, do you
have enough EANx80 for the dive? How much do you have of each?

What are your OTUs and “CNS clock” after the dive?

• If you’ll be diving again in two and a half hours, and you’ll be staying within the
mission averages for three days of diving, how much “CNS clock” time and how
many OTUs can you have on the second dive?

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 12. (Imperial) You plan a dive to 145 feet using a single gas enriched air computer set
for EANx26. You plan to decompress using EANx80 from 30 feet to the surface.
You estimate that your bottom time will be 40 minutes. Your dive tables for
EANx26 show that 40 minutes at 145 feet requires 3 minutes decompression at 40
feet, 10 at 30 feet, 17 at 20 feet and 43 at 10 feet. Your ascent rate is 30 fpm. Your
SAC rate is .8 cubic feet per minute on the working part of the dive, and .65 cf
when decompressing.

• Following the rule of thirds, how much of each gas do you need for this dive?

• If you have twin 104 cf cylinders, working pressure 2400 psi, with 2500 psi of
EANx26 do you have enough EANx26 for the dive? If you have a 104 cf cylinder,
working pressure 2400, with 2300 psi of EANx80, do you have enough EANx80 for
the dive? How much do you have of each?

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®

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• What are your OTUs and “CNS clock” after the dive?

• If you’ll be diving again in two and a half hours, and you’ll be staying within the mis-
sion averages for three days of diving, how much “CNS clock” time and how many
OTUs can you have on the second dive?

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 13. (Metric) You plan a dive to 50 metres using a single gas enriched air computer set
for air. You plan to decompress using oxygen from 6 metres to the surface. Using
desk top software you estimate that your bottom time will be 25 minutes. Using desk
top deco software, you generate air dive tables that show that 25 minutes at 50
metres requires 2 minutes decompression at 9 metres, 4 at 6 metres and 13 at 3
metres. Your ascent rate is 10mpm. Your SAC rate is 22 litres/min on the working
Instructor
part of theGuide
dive, and 18 l /min when decompressing. Appendix

PADI
®

• Following the rule of thirds, how much of each gas do you need for this dive?
A-144 padi.com

If you have twin 21 litre cylinders with 150 bar of air, how much gas volume do you have?

Is it enough for the dive?

At what back gas pressure should you leave the bottom to assure you can complete your
decompression and have a one-third reserve left?

If you have a 7 litre cylinder with 195 bar of oxygen, how much gas volume do you have?

Is it enough for the dive?

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 Appendix Instructor Guide

If
• Ifyou have
you willabe
7 litre cylinder
diving againwith 195 bar
in three of oxygen,
hours, and youhow
willmuch gas volume
be staying dothe
within youmission
have? aver-
ages for five day of diving, how much “CNS clock” time and how many OTUs can you
have on the second dive?

Is it enough for the dive?

• What are your OTUs and “CNS clock” after the dive?
Appendix Instructor Guide

• If you will be diving again in three hours, and you will be staying within the mission aver-
ages for five day of diving, how much “CNS clock” time and how many OTUs can you
have on the second dive? PADI
®

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13. (Imperial) You plan a dive to 165 feet using a single gas enriched air computer set for
air. You plan to decompress using oxygen from 20 feet to the surface. You estimate that
your bottom time will be 25 minutes. Using desk top deco software, you generate air dive
tables that show that 25 minutes at 165 feet requires 2 minutes decompression at 30 feet,
4 at 20 and 13 at 10 feet. Your ascent rate is 30 fpm. Your SAC rate is .78 cf/min on the
working part of the dive and .64 during decompression.

• Following the rule of thirds, how much of each gas do you need for the dive?

13. (Imperial) You plan a dive to 165 feet using a single gas enriched air computer set for
air. You plan to decompress using oxygen from 20 feet to the surface. You estimate that
your bottom time will be 25 minutes. Using desk top deco software, you generate air dive
PADI
®

tables that show that 25 minutes at 165 feet requires 2 minutes decompression at 30 feet,
4 at 20 and 13 at 10 feet. Your ascent rate is 30 fpm. Your SAC rate is .78 cf/min padi.com
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 Instructor Guide Appendix

• If you have twin 120 cubic foot cylinders with a working pressure of 2400 with 2200
psi of air, how much gas volume do you have?

Is it enough for the dive?

At what back gas pressure should you leave at the bottom to assure you can complete
your decompression and have one third reserve left?

If you have a 50 cf cylinder, working pressure 3000, with 2870psi of oxygen, how
much gas volume do you have?

Is it enough for the dive?

• What are your OTUs and “CNS clock” after the dive?

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 Appendix Instructor Guide

• If you will be diving in three hours, and you will be staying within mission averages for
five days of diving, how much “CNS clock” time and how many OTUs can you have on
the second dive?

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 Tec Deep Diver
Digital Manual

Appendix

TEC 40

TEC 45

TEC 50

Main Menu

Tec Deep » Appendix

 APPENDIX
260 Key Formulas
264 CNS Surface Interval Credit Table
264 Oxygen Exposure Limits
265 SAC Conversion Factors
266 Maximum Depths in Feet of Seawater
267 Maximum Depths in Metres of Seawater
268 Equivalent Air Depth and Oxygen
Management Table – Imperial
281 Equivalent Air Depth and Oxygen
Management Table – Metric
295 Tec Deep Diver Statement of
Understanding and Learning Agreement

Appendix 259

APPENDIX
260 Key Formulas
264 CNS Surface Interval Credit Table
264 Oxygen Exposure Limits
265 SAC Conversion Factors
266 Maximum Depths in Feet of Seawater
267 Maximum Depths in Metres of Seawater
268 Equivalent Air Depth and Oxygen
Management Table – Imperial
281 Equivalent Air Depth and Oxygen
Management Table – Metric
295 Tec Deep Diver Statement of
Understanding and Learning Agreement

Appendix 259

Tec Deep » Appendix Main Menu Tec 40 Menu Tec 45 Menu Tec 50 Menu APX-259
 Key Formulas

Equivalent Air Depth (EAD) Formula

METRIC

(1-fraction of oxygen) x (Depth in metres+10)

EAD = -10
.79

IMPERIAL

(1-fraction of oxygen) x (Depth in feet+33)

EAD = -33
.79

Maximum Depth Formulas

METRIC

Bottom max depth (1.4 ata) = ( fraction 14of oxygen ) - 10

Deco max depth (1.6 ata) = (
fraction of oxygen )
16 - 10

IMPERIAL

Bottom max depth (1.4 ata) = ( fraction46.2

of oxygen )
- 33

Deco max depth (1.6 ata) = (

fraction of oxygen )
52.8 - 33

The T Formula
Where:
PO2 PO2 = partial pressure of oxygen in ata
FO2 P FO2 = the fraction of oxygen in the blend
and P = absolute pressure in ata

260 Tec Deep Diver Manual

Tec Deep » Appendix Main Menu Tec 40 Menu Tec 45 Menu Tec 50 Menu APX-260
 Finding Your Surface Air Consumption (SAC) Rate Formula
METRIC

litres per minute SAC = bar used x total cylinder capacity litres ÷ min
(depth in metres + 10) ÷ 10
Example: You use 25 bar with twin 12 litre cylinders (total 24 litres capacity) while
swimming at 15 metres for 10 minutes.
25 x 24 600 ÷ 10 = 24 litres per minute SAC rate
÷ 10 =
(15 + 10) ÷ 10 2.5

IMPERIAL

cf per min SAC = (psi used ÷ working pressure) x total cylinder capacity ÷ min
(depth in feet + 33) ÷ 33
Example: You use 370 psi with twin 71 cubic foot cylinders (142 total capacity, work-
ing pressure 2475 psi) while swimming at 50 feet for 10 minutes.
(370 ÷ 2475) x 142 ÷ 10 = 21.2 ÷ 10 = .84 cubic feet per minute SAC rate
(50 + 33) ÷ 33 2.5

Gas Requirement Estimate Formulas

METRIC
litres required
= (min x SAC rate) x ((depth in metres + 10) ÷ 10)

Example: If your SAC rate is 22 litres per minute, how much gas supply do you
need for 15 minutes at 33 metres?
litres required = (15 x 22) x ((33 + 10) ÷ 10)
litres required = 330 x 4.3
litres required = 1419

IMPERIAL
cubic feet required
= (min x SAC rate) x ((depth in feet + 33) ÷ 33)

Example: If your SAC rate is .77 cubic feet per minute, how
much gas supply do you need for 15 minutes at 110 feet?
cubic feet required = (15 x .77) x ((110 + 33) ÷ 33)
cubic feet required = 11.6 x 4.3
cubic feet required = 49.9

Appendix 261

Tec Deep » Appendix Main Menu Tec 40 Menu Tec 45 Menu Tec 50 Menu APX-261
 Gas Reserve Formula
gas volume required = total gas
(1 - reserve)
METRIC
For example: If you estimate you need 1419 litres of a gas, what’s your gas
requirement with a 33 percent reserve?
1419 = 1419 = 2150 litres
(1 - .33) .66
IMPERIAL
For example: If you estimate you need 49.9 cubic feet of a gas, what’s your gas
requirement with a 33 percent reserve?
49.9 49.9
= = 75.6 cubic feet
(1 - .33) .66

Rule of Thirds “Shortcut” Formula

gas volume required x 1.5 = total gas

Actual Gas Supply Formulas

METRIC
designated volume in litres x pressure in bar = available volume in litres

IMPERIAL
actual pressure in psi ÷ working pressure in psi x capacity in cubic feet = available
volume in cubic feet

Actual Gas Supply, Imperial Baseline Method

capacity in cubic feet ÷ working pressure in psi = baseline

baseline x actual pressure in psi = available volume in cubic feet

Ascent Depth Formula

ascent depth = ((bottom depth - first stop depth) ÷ 2) + first stop depth

262 Tec Deep Diver Manual

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 Ascent Time To First Stop Forumla
ascent time = (bottom depth - first stop depth) ÷ ascent rate

Gas Requirement Estimate Using Conversion Factor Formula

gas required = SAC x minutes x conversion factor

Back Gas Turn Pressure Formula

METRIC
turn pressure = start pressure - (bottom volume ÷ cylinder capacity)

IMPERIAL
turn pressure = start pressure - (bottom volume ÷ cylinder baseline)

Gas Matching Formulas

METRIC

small supply reserve pressure = (large supply volume ÷ 3) ÷ small supply cylin-
der capacity

small supply turn pressure = small supply actual pressure - ((small supply
actual pressure - small supply reserve pressure) ÷ 2)

IMPERIAL

small supply reserve pressure = (large supply volume ÷ 3) ÷ small supply cylin-
der baseline

small supply turn pressure = small supply actual pressure - ((small supply
actual pressure - small supply reserve pressure) ÷ 2)

Appendix 263

Tec Deep » Appendix Main Menu Tec 40 Menu Tec 45 Menu Tec 50 Menu APX-263
 CNS SURFACE INTERVAL CREDIT TABLE
Starting 0:00 – 0:31 – 1:01 – 1:31 – 2:01 – 3:01 – 4:01 – 6:01 –
CNS% 0:30 1:00 1:30 2:00 3:00 4:00 6:00 9:00
10% 10% 8% 6% 5% 4% 3% 2% 1%
20% 20% 16% 13% 10% 8% 5% 3% 1%
30% 30% 24% 19% 15% 12% 8% 5% 2%
40% 40% 32% 25% 20% 16% 10% 6% 2%
50% 50% 40% 32% 25% 20% 13% 8% 3%
55% 55% 44% 35% 28% 22% 14%  9% 3%
60% 60% 48% 38% 30% 24% 15% 10% 4%
65% 65% 52% 41% 33% 26% 16% 10% 4%
70% 70% 56% 44% 35% 28% 18% 11% 4%
75% 75% 60% 47% 38% 30% 19% 12% 5%
80% 80% 64% 50% 40% 32% 20% 13% 5%
85% 85% 68% 54% 43% 34% 21% 14% 5%
90% 90% 72% 57% 45% 36% 23% 14% 5%
95% 95% 76% 60% 48% 38% 24% 15% 6%
100% 100% 80% 63% 50% 40% 25% 16% 6%

OXYGEN EXPOSURE LIMITS

Oxygen Tolerance Units
NOAA Oxygen Exposure Limits Exposure Limits
Single Total in Average
PO2 Total OTUs
Exposure 24 Hours Days OTUs
for Mission Per Day
0.6 720 720
0.7 570 570 1 850 850
0.8 450 450 2 1400 700
0.9 360 360 3 1860 620
1 300 300 4 2100 525
1.1 240 270 5 2300 460
1.2 210 240 6 2520 420
1.3 180 210 7 2660 380
1.4 150 180 8 2800 350
1.5 120 180 9 2970 330
1.6 45 150 10 3100 310
11 3300 300
12 3600 300
13 3900 300
14 4200 300
15-30 as required 300
264 Tec Deep Diver Manual

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 SAC CONVERSION FACTORS
Multiply your SAC rate by the factor to determine your gas comsumption rate at depth.

Metric Imperial
Depth (m) Conversion Factor Depth (ft) Conversion Factor
3 1.3 10 1.3
5 1.5 15 1.5
6 1.6 20 1.6
9 1.9 30 1.9
12 2.2 40 2.2
15 2.5 50 2.5
18 2.8 60 2.8
21 3.1 70 3.1
24 3.4 80 3.4
27 3.7 90 3.7
30 4.0 100 4.0
33 4.3 110 4.3
36 4.6 120 4.6
39 4.9 130 4.9
42 5.2 140 5.2
45 5.5 150 5.5
48 5.8 160 5.8
50 6.0 165 6.0
54 6.4 170 6.2
57 6.7 180 6.5

Appendix 265

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 MAXIMUM DEPTHS IN FEET OF SEAWATER
BLEND @1.4 @1.6 BLEND @1.4 @1.6
21% 187 218 60% 44 55
22% 177 207 61% 43 54
23% 168 197 62% 42 52
24% 160 187 63% 40 51
25% 152 178 64% 39 50
26% 145 170 65% 38 48
27% 138 163 66% 37 47
28% 132 156 67% 36 46
29% 126 149 68% 35 45
30% 121 143 69% 34 44
31% 116 137 70% 33 42
32% 111 132 71% 32 41
33% 107 127 72% 31 40
34% 103 122 73% 30 39
35% 99 118 74% 29 38
36% 95 114 75% 29 37
37% 92 110 76% 28 36
38% 89 106 77% 27 36
39% 85 102 78% 26 35
40% 83 99 79% 25 34
41% 80 96 80% 25 33
42% 77 93 81% 24 32
43% 74 90 82% 23 31
44% 72 87 83% 23 31
45% 70 84 84% 22 30
46% 67 82 85% 21 29
47% 65 79 86% 21 28
48% 63 77 87% 20 28
49% 61 75 88% 20 27
50% 59 73 89% 19 26
51% 58 71 90% 18 26
52% 56 69 91% 18 25
53% 54 67 92% 17 24
54% 53 65 93% 17 24
55% 51 63 94% 16 23
56% 49 61 95% 16 23
57% 48 60 96% 15 22
58% 47 58 97% 15 21
59% 45 56 98% 14 21
99% 14 20
266 Tec Deep Diver Manual 100% 13 20

Tec Deep » Appendix Main Menu Tec 40 Menu Tec 45 Menu Tec 50 Menu APX-266
 MAXIMUM DEPTHS IN METRES OF SEAWATER
BLEND @1.4 @1.6 BLEND @1.4 @1.6
21% 57 66 60% 13 17
22% 54 63 61% 13 16
23% 51 60 62% 13 16
24% 48 57 63% 12 15
25% 46 54 64% 12 15
26% 44 52 65% 12 15
27% 42 49 66% 11 14
28% 40 47 67% 11 14
29% 38 45 68% 11 14
30% 37 43 69% 10 13
31% 35 42 70% 10 13
32% 34 40 71% 10 13
33% 32 38 72% 9 12
34% 31 37 73% 9 12
35% 30 36 74% 9 12
36% 29 34 75% 9 11
37% 28 33 76% 8 11
38% 27 32 77% 8 11
39% 26 31 78% 8 11
40% 25 30 79% 8 10
41% 24 29 80% 8 10
42% 23 28 81% 7 10
43% 23 27 82% 7 10
44% 22 26 83% 7 9
45% 21 26 84% 7 9
46% 20 25 85% 6 9
47% 20 24 86% 6 9
48% 19 23 87% 6 8
49% 19 23 88% 6 8
50% 18 22 89% 6 8
51% 17 21 90% 6 8
52% 17 21 91% 5 8
53% 16 20 92% 5 7
54% 16 20 93% 5 7
55% 15 19 94% 5 7
56% 15 19 95% 5 7
57% 15 18 96% 5 7
58% 14 18 97% 4 6
59% 14 17 98% 4 6
99% 4 6
100% 4 6 267

Tec Deep » Appendix Main Menu Tec 40 Menu Tec 45 Menu Tec 50 Menu APX-267
 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE IMPERIAL
OXYGEN CONTENT 21% OXYGEN CONTENT 22%
OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 10 0.27 –– 0.00% 10 9 0.29 –– 0.00%
15 15 0.31 –– 0.00% 15 14 0.32 –– 0.00%
20 20 0.34 –– 0.00% 20 19 0.35 –– 0.00%
30 30 0.40 –– 0.00% 30 29 0.42 –– 0.00%
40 40 0.46 –– 0.00% 40 39 0.49 –– 0.00%
50 50 0.53 0.09 0.14% 50 49 0.55 0.16 0.14%
60 60 0.59 0.24 0.14% 60 59 0.62 0.31 0.17%
70 70 0.66 0.38 0.17% 70 69 0.69 0.44 0.17%
80 80 0.72 0.50 0.22% 80 79 0.75 0.57 0.22%
90 90 0.78 0.62 0.22% 90 88 0.82 0.69 0.28%
100 100 0.85 0.74 0.28% 100 98 0.89 0.81 0.28%
110 110 0.91 0.85 0.33% 110 108 0.95 0.92 0.33%%
120 120 0.97 0.96 0.33% 120 118 1.02 1.03 0.42%
130 130 1.04 1.06 0.42% 130 128 1.09 1.14 0.42%
140 140 1.10 1.16 0.42% 140 138 1.15 1.25 0.48%
150 150 1.16 1.27 0.48% 150 148 1.22 1.35 0.55%
160 160 1.23 1.37 0.55% 160 158 1.29 1.46 0.55%
170 170 1.29 1.46 0.55% 170 167 1.35 1.56 0.67%
180 180 1.36 1.56 0.67% 180 177 1.42 1.66 0.83%

OXYGEN CONTENT 23% OXYGEN CONTENT 24%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 8 0.31 –– 0.00%
10 9 0.30 –– 0.00%
15 13 0.35 –– 0.00%
15 14 0.33 –– 0.00%
20 18 0.39 –– 0.00%
20 19 0.37 –– 0.00%
30 28 0.46 –– 0.00%
30 28 0.44 –– 0.00%
40 37 0.53 0.10 0.14%
40 38 0.51 0.03 0.14%
50 47 0.60 0.27 0.14%
50 48 0.58 0.22 0.14%
60 56 0.68 0.42 0.17%
60 58 0.65 0.36 0.17%
70 66 0.75 0.56 0.22%
70 67 0.72 0.50 0.22%
80 76 0.82 0.69 0.28%
80 77 0.79 0.63 0.22%
90 85 0.89 0.82 0.28%
90 87 0.86 0.76 0.28%
100 95 0.97 0.95 0.33%
100 97 0.93 0.88 0.33%
110 105 1.04 1.07 0.42%
110 106 1.00 0.99 0.33%
120 114 1.11 1.18 0.48%
120 116 1.07 1.11 0.42%
130 124 1.19 1.30 0.48%
130 126 1.14 1.22 0.48%
140 133 1.26 1.41 0.55%
140 136 1.21 1.33 0.55%
150 143 1.33 1.52 0.67%
150 145 1.28 1.44 0.55%
160 153 1.40 1.63 0.67%
160 155 1.35 1.55 0.67%
170 162 1.48 1.74 0.83%
170 165 1.41 1.65 0.83%
180 172 1.55 1.85 2.22%
268 180 175 1.48 1.75 0.83%

Tec Deep » Appendix Main Menu Tec 40 Menu Tec 45 Menu Tec 50 Menu APX-268
 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – IMPERIAL (continued)

OXYGEN CONTENT 25% OXYGEN CONTENT 26%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 8 0.33 –– 0.00% 10 7 0.34 –– 0.00%
15 13 0.36 –– 0.00% 15 12 0.38 –– 0.00%
20 17 0.40 –– 0.00% 20 17 0.42 –– 0.00%
30 27 0.48 –– 0.00% 30 26 0.50 –– 0.00%
40 36 0.55 0.16 0.14% 40 35 0.58 0.21 0.14%
50 46 0.63 0.32 0.17% 50 45 0.65 0.38 0.17%
60 55 0.70 0.48 0.17% 60 54 0.73 0.53 0.22%
70 65 0.78 0.62 0.22% 70 63 0.81 0.68 0.28%
80 74 0.86 0.75 0.28% 80 73 0.89 0.81 0.28%
90 84 0.93 0.89 0.33% 90 82 0.97 0.95 0.33%
100 93 1.01 1.01 0.42% 100 92 1.05 1.08 0.42%
110 103 1.08 1.14 0.42% 110 101 1.13 1.21 0.48%
120 112 1.16 1.26 0.48% 120 110 1.21 1.33 0.55%
130 122 1.23 1.38 0.55% 130 120 1.28 1.45 0.55%
140 131 1.31 1.49 0.67% 140 129 1.36 1.57 0.67%
150 141 1.39 1.61 0.67% 150 138 1.44 1.69 0.83%
160 150 1.46 1.72 0.83% 160 148 1.52 1.81 2.22%
170 160 1.54 1.83 2.22% 170 157 1.60 1.92 2.22%
180 169 1.61 1.94 2.22%

OXYGEN CONTENT 27% OXYGEN CONTENT 28%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 7 0.35 –– 0.00% 10 6 0.36 –– 0.00%
15 11 0.39 –– 0.00% 15 11 0.41 –– 0.00%
20 16 0.43 –– 0.00% 20 15 0.45 –– 0.00%
30 25 0.52 0.06 0.14% 30 24 0.53 0.11 0.14%
40 34 0.60 0.26 0.14% 40 34 0.62 0.30 0.17%
50 44 0.68 0.43 0.17% 50 43 0.70 0.48 0.17%
60 53 0.76 0.58 0.22% 60 52 0.79 0.63 0.22%
70 62 0.84 0.73 0.28% 70 61 0.87 0.79 0.28%
80 71 0.92 0.87 0.33% 80 70 0.96 0.93 0.33%
90 81 1.01 1.01 0.42% 90 79 1.04 1.07 0.42%
100 90 1.09 1.14 0.42% 100 88 1.13 1.21 0.48%
110 99 1.17 1.27 0.48% 110 97 1.21 1.34 0.55%
120 108 1.25 1.40 0.55% 120 106 1.30 1.47 0.55%
130 118 1.33 1.53 0.67% 130 116 1.38 1.60 0.67%
140 127 1.42 1.65 0.83% 140 125 1.47 1.73 0.83%
150 136 1.50 1.77 0.83% 150 134 1.55 1.86 2.22%
160 145 1.58 1.89 2.22%

Appendix 269

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – IMPERIAL (continued)

OXYGEN CONTENT 29% OXYGEN CONTENT 30%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 6 0.38 –– 0.00% 10 5 0.39 –– 0.00%
15 10 0.42 –– 0.00% 15 10 0.44 –– 0.00%
20 15 0.47 –– 0.00% 20 14 0.48 –– 0.00%
30 24 0.55 0.16 0.14% 30 23 0.57 0.20 0.14%
40 33 0.64 0.35 0.17% 40 32 0.66 0.40 0.17%
50 42 0.73 0.52 0.22% 50 41 0.75 0.57 0.22%
60 51 0.82 0.69 0.28% 60 49 0.85 0.74 0.28%
70 60 0.91 0.84 0.33% 70 58 0.94 0.89 0.33%
80 69 0.99 0.99 0.33% 80 67 1.03 1.05 0.42%
90 78 1.08 1.13 0.42% 90 76 1.12 1.19 0.48%
100 87 1.17 1.27 0.48% 100 85 1.21 1.34 0.55%
110 96 1.26 1.41 0.55% 110 94 1.30 1.48 0.55%
120 105 1.34 1.55 0.67% 120 103 1.39 1.62 0.67%
130 113 1.43 1.68 0.83% 130 111 1.48 1.75 0.83%
140 122 1.52 1.81 2.22% 140 120 1.57 1.88 2.22%
150 131 1.61 1.94 2.22%

OXYGEN CONTENT 31% OXYGEN CONTENT 32%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 5 0.40 –– 0.00% 10 4 0.42 –– 0.00%
15 9 0.45 –– 0.00% 15 8 0.47 –– 0.00%
20 13 0.50 –– 0.00% 20 13 0.51 0.05 0.14%
30 22 0.59 0.24 0.14% 30 21 0.61 0.29 0.17%
40 31 0.69 0.44 0.17% 40 30 0.71 0.48 0.22%
50 39 0.78 0.62 0.22% 50 38 0.80 0.66 0.22%
60 48 0.87 0.79 0.28% 60 47 0.90 0.83 0.28%
70 57 0.97 0.95 0.33% 70 56 1.00 1.00 0.33%
80 66 1.06 1.10 0.42% 80 64 1.10 1.16 0.42%
90 74 1.16 1.25 0.48% 90 73 1.19 1.31 0.48%
100 83 1.25 1.40 0.55% 100 81 1.29 1.46 0.55%
110 92 1.34 1.54 0.67% 110 90 1.39 1.61 0.67%
120 101 1.44 1.68 0.83% 120 99 1.48 1.75 0.83%
130 109 1.53 1.82 2.22% 130 107 1.58 1.90 2.22%

270 Tec Deep Diver Manual

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – IMPERIAL (continued)

OXYGEN CONTENT 33% OXYGEN CONTENT 34%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 3 0.43 –– 0.00% 10 3 0.44 –– 0.00%
15 8 0.48 –– 0.00% 15 7 0.49 –– 0.00%
20 12 0.53 0.10 0.14% 20 11 0.55 0.14 0.14%
30 20 0.63 0.33 0.17% 30 20 0.65 0.37 0.17%
40 29 0.73 0.52 0.22% 40 28 0.75 0.57 0.22%
50 37 0.83 0.71 0.28% 50 36 0.86 0.75 0.28%
60 46 0.93 0.88 0.33% 60 45 0.96 0.93 0.33%
70 54 1.03 1.05 0.42% 70 53 1.06 1.10 0.42%
80 63 1.13 1.21 0.48% 80 61 1.16 1.27 0.48%
90 71 1.23 1.37 0.55% 90 70 1.27 1.43 0.55%
100 80 1.33 1.52 0.67% 100 78 1.37 1.58 0.67%
110 88 1.43 1.67 0.83% 110 86 1.47 1.74 0.83%
120 97 1.53 1.82 2.22% 120 95 1.58 1.89 2.22%

OXYGEN CONTENT 35% OXYGEN CONTENT 36%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 2 0.46 –– 0.00% 10 2 0.47 –– 0.00%
15 6 0.51 0.04 0.14% 15 6 0.52 0.08 0.14%
20 11 0.56 0.18 0.14% 20 10 0.58 0.21 0.14%
30 19 0.67 0.40 0.17% 30 18 0.69 0.44 0.17%
40 27 0.77 0.61 0.22% 40 26 0.80 0.65 0.22%
50 35 0.88 0.80 0.28% 50 34 0.91 0.84 0.33%
60 44 0.99 0.98 0.33% 60 42 1.01 1.02 0.42%
70 52 1.09 1.15 0.42% 70 50 1.12 1.20 0.48%
80 60 1.20 1.32 0.48% 80 59 1.23 1.37 0.55%
90 68 1.30 1.48 0.55% 90 67 1.34 1.54 0.67%
100 76 1.41 1.64 0.83% 100 75 1.45 1.70 0.83%
110 85 1.52 1.80 2.22% 110 83 1.56 1.87 2.22%

Appendix 271

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – IMPERIAL (continued)

OXYGEN CONTENT 37% OXYGEN CONTENT 38%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 1 0.48 #NUM! 0.00% 10 1 0.50 #NUM! 0.00%
15 5 0.54 0.12 0.14% 15 5 0.55 0.15 0.14%
20 9 0.59 0.25 0.14% 20 9 0.61 0.29 0.17%
30 17 0.71 0.48 0.22% 30 16 0.73 0.52 0.22%
40 25 0.82 0.69 0.28% 40 24 0.84 0.73 0.28%
50 33 0.93 0.88 0.33% 50 32 0.96 0.93 0.33%
60 41 1.04 1.07 0.42% 60 40 1.07 1.12 0.42%
70 49 1.15 1.25 0.48% 70 48 1.19 1.30 0.48%
80 57 1.27 1.43 0.55% 80 56 1.30 1.48 0.55%
90 65 1.38 1.60 0.67% 90 64 1.42 1.65 0.83%
100 73 1.49 1.76 0.83% 100 71 1.53 1.82 2.22%
110 81 1.60 1.93 2.22%

OXYGEN CONTENT 39% OXYGEN CONTENT 40%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 0 0.51 0.03 0.14% 10 0 0.52 0.07 0.14%
15 4 0.57 0.19 0.14% 15 3 0.58 0.22 0.14%
20 8 0.63 0.32 0.17% 20 7 0.64 0.35 0.17%
30 16 0.74 0.55 0.22% 30 15 0.76 0.59 0.22%
40 23 0.86 0.77 0.28% 40 22 0.88 0.80 0.28%
50 31 0.98 0.97 0.33% 50 30 1.01 1.01 0.42%
60 39 1.10 1.16 0.42% 60 38 1.13 1.21 0.48%
70 47 1.22 1.35 0.55% 70 45 1.25 1.40 0.55%
80 54 1.34 1.53 0.67% 80 53 1.37 1.58 0.67%
90 62 1.45 1.71 0.83% 90 60 1.49 1.76 0.83%
100 70 1.57 1.88 2.22% 100 68 1.61 1.94 2.22%

272 Tec Deep Diver Manual

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – IMPERIAL (continued)

OXYGEN CONTENT 41% OXYGEN CONTENT 42%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -1 0.53 0.11 0.14% 10 -1 0.55 0.14 0.14%
15 3 0.60 0.25 0.14% 15 2 0.61 0.29 0.17%
20 7 0.66 0.39 0.17% 20 6 0.67 0.42 0.17%
30 14 0.78 0.62 0.22% 30 13 0.80 0.66 0.22%
40 22 0.91 0.84 0.33% 40 21 0.93 0.88 0.33%
50 29 1.03 1.05 0.42% 50 28 1.06 1.09 0.42%
60 36 1.16 1.25 0.48% 60 35 1.18 1.30 0.48%
70 44 1.28 1.45 0.55% 70 43 1.31 1.49 0.67%
80 51 1.40 1.63 0.67% 80 50 1.44 1.69 0.83%
90 59 1.53 1.82 2.22% 90 57 1.57 1.87 2.22%

OXYGEN CONTENT 43% OXYGEN CONTENT 44%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -2 0.56 0.17 0.14% 10 -3 0.57 0.20 0.14%
15 2 0.63 0.32 0.17% 15 1 0.64 0.35 0.17%
20 5 0.69 0.45 0.17% 20 5 0.71 0.48 0.22%
30 12 0.82 0.69 0.28% 30 12 0.84 0.73 0.28%
40 20 0.95 0.92 0.33% 40 19 0.97 0.96 0.33%
50 27 1.08 1.13 0.42% 50 26 1.11 1.17 0.48%
60 34 1.21 1.34 0.55% 60 33 1.24 1.38 0.55%
70 41 1.34 1.54 0.67% 70 40 1.37 1.59 0.67%
80 49 1.47 1.74 0.83% 80 47 1.51 1.79 2.22%
90 56 1.60 1.93 2.22%

OXYGEN CONTENT 45% OXYGEN CONTENT 46%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -3 0.59 0.23 0.14% 10 -4 0.60 0.26 0.14%
15 0 0.65 0.38 0.17% 15 0 0.67 0.41 0.17%
20 4 0.72 0.51 0.22% 20 3 0.74 0.54 0.22%
30 11 0.86 0.76 0.28% 30 10 0.88 0.79 0.28%
40 18 1.00 0.99 0.33% 40 17 1.02 1.03 0.42%
50 25 1.13 1.21 0.48% 50 24 1.16 1.25 0.48%
60 32 1.27 1.43 0.55% 60 31 1.30 1.47 0.55%
70 39 1.40 1.64 0.67% 70 37 1.44 1.68 0.83%
80 46 1.54 1.84 2.22% 80 44 1.58 1.89 2.22%

Appendix 273

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – IMPERIAL (continued)

OXYGEN CONTENT 47% OXYGEN CONTENT 48%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -4 0.61 0.29 0.17% 10 -5 0.63 0.32 0.17%
15 -1 0.68 0.44 0.17% 15 -1 0.70 0.46 0.17%
20 3 0.75 0.57 0.22% 20 2 0.77 0.60 0.22%
30 9 0.90 0.83 0.28% 30 8 0.92 0.86 0.33%
40 16 1.04 1.07 0.42% 40 15 1.06 1.10 0.42%
50 23 1.18 1.29 0.48% 50 22 1.21 1.33 0.55%
60 29 1.32 1.51 0.67% 60 28 1.35 1.56 0.67%
70 36 1.47 1.73 0.83% 70 35 1.50 1.78 0.83%
80 43 1.61 1.94 2.22%

OXYGEN CONTENT 49% OXYGEN CONTENT 50%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -5 0.64 0.34 0.17% 10 -6 0.65 0.37 0.17%
15 -2 0.71 0.49 0.22% 15 -3 0.73 0.52 0.22%
20 1 0.79 0.63 0.22% 20 1 0.80 0.66 0.22%
30 8 0.94 0.89 0.33% 30 7 0.95 0.92 0.33%
40 14 1.08 1.14 0.42% 40 13 1.11 1.17 0.48%
50 21 1.23 1.37 0.55% 50 20 1.26 1.41 0.55%
60 27 1.38 1.60 0.67% 60 26 1.41 1.64 0.83%
70 33 1.53 1.82 2.22% 70 32 1.56 1.87 2.22%

OXYGEN CONTENT 51% OXYGEN CONTENT 52%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -6 0.66 0.40 0.17% 10 -7 0.68 0.42 0.17%
15 -3 0.74 0.55 0.22% 15 -4 0.76 0.57 0.22%
20 0 0.82 0.69 0.28% 20 -1 0.84 0.72 0.28%
30 6 0.97 0.96 0.33% 30 5 0.99 0.99 0.33%
40 12 1.13 1.21 0.48% 40 11 1.15 1.24 0.48%
50 18 1.28 1.45 0.55% 50 17 1.31 1.49 0.67%
60 25 1.44 1.68 0.83% 60 24 1.47 1.73 0.83%
70 31 1.59 1.91 2.22%

274 Tec Deep Diver Manual

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – IMPERIAL (continued)

OXYGEN CONTENT 53% OXYGEN CONTENT 54%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -7 0.69 0.45 0.17% 10 -8 0.70 0.47 0.17%
15 -4 0.77 0.60 0.22% 15 -5 0.79 0.63 0.22%
20 -1 0.85 0.75 0.28% 20 -2 0.87 0.77 0.28%
30 4 1.01 1.02 0.42% 30 4 1.03 1.05 0.42%
40 10 1.17 1.28 0.48% 40 10 1.19 1.31 0.48%
50 16 1.33 1.53 0.67% 50 15 1.36 1.57 0.67%
60 22 1.49 1.77 0.83% 60 21 1.52 1.81 2.22%

OXYGEN CONTENT 55% OXYGEN CONTENT 56%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -9 0.72 0.50 0.22% 10 -9 0.73 0.52 0.22%
15 -6 0.80 0.65 0.22% 15 -6 0.81 0.68 0.28%
20 -3 0.88 0.80 0.28% 20 -3 0.90 0.83 0.28%
30 3 1.05 1.08 0.42% 30 2 1.07 1.11 0.42%
40 9 1.22 1.35 0.55% 40 8 1.24 1.38 0.55%
50 14 1.38 1.60 0.67% 50 13 1.41 1.64 0.83%
60 20 1.55 1.85 2.22% 60 19 1.58 1.89 2.22%

OXYGEN CONTENT 57% OXYGEN CONTENT 58%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -10 0.74 0.55 0.22% 10 -10 0.76 0.57 0.22%
15 -7 0.83 0.71 0.28% 15 -7 0.84 0.73 0.28%
20 -4 0.92 0.86 0.33% 20 -5 0.93 0.88 0.33%
30 1 1.09 1.14 0.42% 30 0 1.11 1.18 0.48%
40 7 1.26 1.42 0.55% 40 6 1.28 1.45 0.55%
50 12 1.43 1.68 0.83% 50 11 1.46 1.72 0.83%
60 18 1.61 1.93 2.22%

Appendix 275

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – IMPERIAL (continued)

OXYGEN CONTENT 59% OXYGEN CONTENT 60%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -11 0.77 0.60 0.22% 10 -11 0.78 0.62 0.22%
15 -8 0.86 0.76 0.28% 15 -9 0.87 0.78 0.28%
20 -5 0.95 0.91 0.33% 20 -6 0.96 0.94 0.33%
30 0 1.13 1.21 0.48% 30 -1 1.15 1.24 0.48%
40 5 1.31 1.49 0.67% 40 4 1.33 1.52 0.67%
50 10 1.48 1.75 0.83% 50 9 1.51 1.79 2.22%

OXYGEN CONTENT 61% OXYGEN CONTENT 62%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

10 -12 0.79 0.65 0.22% 10 -12 0.81 0.67 0.28%

15 -9 0.89 0.81 0.28% 15 -10 0.90 0.83 0.28%
20 -7 0.98 0.97 0.33% 20 -8 1.00 0.99 0.33%
30 -2 1.16 1.27 0.48% 30 -3 1.18 1.30 0.48%
40 3 1.35 1.55 0.67% 40 2 1.37 1.59 0.67%
50 8 1.53 1.83 2.22% 50 7 1.56 1.86 2.22%

OXYGEN CONTENT 63% OXYGEN CONTENT 64%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Mi

10 -13 0.82 0.69 0.28% 10 -13 0.83 0.72 0.28%

15 -11 0.92 0.86 0.33% 15 -11 0.93 0.88 0.33%
20 -8 1.01 1.02 0.42% 20 -9 1.03 1.05 0.42%
30 -3 1.20 1.33 0.48% 30 -4 1.22 1.36 0.55%
40 1 1.39 1.62 0.67% 40 0 1.42 1.65 0.83%
50 6 1.58 1.90 2.22% 50 5 1.61 1.94 2.22%

OXYGEN CONTENT 65% OXYGEN CONTENT 66%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

10 -14 0.85 0.74 0.28% 10 -14 0.86 0.76 0.28%

15 -12 0.95 0.91 0.33% 15 -12 0.96 0.93 0.33%
20 -10 1.04 1.07 0.42% 20 -10 1.06 1.10 0.42%
30 -5 1.24 1.39 0.55% 30 -6 1.26 1.42 0.55%
40 -1 1.44 1.69 0.83% 40 -2 1.46 1.72 0.83%

276 Tec Deep Diver Manual

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – IMPERIAL (continued)

OXYGEN CONTENT 67% OXYGEN CONTENT 68%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -15 0.87 0.78 0.28%
10 -16 0.89 0.81 0.28%
15 -13 0.97 0.96 0.33%
15 -14 0.99 0.98 0.33%
20 -11 1.08 1.12 0.42%
20 -12 1.09 1.15 0.42%
30 -7 1.28 1.45 0.55%
30 -7 1.30 1.47 0.55%
40 -3 1.48 1.75 0.83%
40 -3 1.50 1.78 0.83%

OXYGEN CONTENT 69% OXYGEN CONTENT 70%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

10 -16 0.90 0.83 0.28% 10 -17 0.91 0.85 0.33%

15 -14 1.00 1.01 0.33% 15 -15 1.02 1.03 0.42%
20 -12 1.11 1.18 0.48% 20 -13 1.12 1.20 0.48%
30 -8 1.32 1.50 0.67% 30 -9 1.34 1.53 0.67%
40 -4 1.53 1.82 2.22% 40 -5 1.55 1.85 2.22%

OXYGEN CONTENT 71% OXYGEN CONTENT 72%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -17 0.93 0.87 0.33% 10 -18 0.94 0.90 0.33%
15 -15 1.03 1.05 0.42% 15 -16 1.05 1.08 0.42%
20 -14 1.14 1.23 0.48% 20 -14 1.16 1.25 0.48%
30 -10 1.36 1.56 0.67% 30 -11 1.37 1.59 0.67%
40 -6 1.57 1.88 2.22% 40 -7 1.59 1.91 2.22%

OXYGEN CONTENT 73% OXYGEN CONTENT 74%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -19 0.96 0.94 0.33%
10 -18 0.95 0.92 0.33%
15 -17 1.08 1.13 0.42%
15 -17 1.06 1.10 0.42%
20 -16 1.19 1.30 0.48%
20 -15 1.17 1.28 0.48%
30 -12 1.41 1.65 0.83%
30 -11 1.39 1.62 0.67%
40 -8 1.61 1.95 2.22%

Appendix 277

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – IMPERIAL (continued)

OXYGEN CONTENT 75% OXYGEN CONTENT 76%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -19 0.98 0.96 0.33%
10 -20 0.99 0.98 0.33%
15 -18 1.09 1.15 0.42%
15 -18 1.11 1.17 0.48%
20 -16 1.20 1.33 0.48%
20 -17 1.22 1.35 0.55%
30 -13 1.43 1.68 0.83%
30 -14 1.45 1.70 0.83%

OXYGEN CONTENT 77% OXYGEN CONTENT 78%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

10 -20 1.00 1.01 0.33% 10 -21 1.02 1.03 0.42%

15 -19 1.12 1.20 0.48% 15 -20 1.13 1.22 0.48%
20 -18 1.24 1.38 0.55% 20 -18 1.25 1.40 0.55%
30 -15 1.47 1.73 0.83% 30 -15 1.49 1.76 0.83%

OXYGEN CONTENT 79% OXYGEN CONTENT 80%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -22 1.04 1.07 0.42%
10 -22 1.03 1.05 0.42%
15 -21 1.16 1.26 0.48%
15 -20 1.15 1.24 0.48%
20 -20 1.28 1.45 0.55%
20 -19 1.27 1.43 0.55%
30 -17 1.53 1.82 2.22%
30 -16 1.51 1.79 2.22%

OXYGEN CONTENT 81% OXYGEN CONTENT 82%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

10 -23 1.06 1.09 0.42% 10 -23 1.07 1.11 0.42%

15 -21 1.18 1.29 0.48% 15 -22 1.19 1.31 0.48%
20 -20 1.30 1.48 0.55% 20 -21 1.32 1.50 0.67%
30 -18 1.55 1.85 2.22% 30 -19 1.57 1.87 2.22%

OXYGEN CONTENT 83% OXYGEN CONTENT 84%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min
Min
10 -24 1.08 1.13 0.42% 10 -24 1.09 1.15 0.42%
15 -23 1.21 1.33 0.55% 15 -23 1.22 1.36 0.55%
20 -22 1.33 1.53 0.67% 20 -22 1.35 1.55 0.67%
30 -19 1.58 1.90 2.22% 30 -20 1.60 1.93 2.22%

278 Tec Deep Diver Manual

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – IMPERIAL (continued)

OXYGEN CONTENT 85% OXYGEN CONTENT 86%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

10 -25 1.11 1.18 0.48% 10 -25 1.12 1.20 0.48%

15 -24 1.24 1.38 0.55% 15 -24 1.25 1.40 0.55%
20 -23 1.37 1.58 0.67% 20 -24 1.38 1.60 0.67%

OXYGEN CONTENT 87% OXYGEN CONTENT 88%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -26 1.13 1.22 0.48% 10 -26 1.15 1.24 0.48%
15 -25 1.27 1.42 0.55% 15 -26 1.28 1.45 0.55%
20 -24 1.40 1.62 0.67% 20 -25 1.41 1.65 0.83%

OXYGEN CONTENT 89% OXYGEN CONTENT 90%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

10 -27 1.16 1.26 0.48% 10 -28 1.17 1.28 0.48%

15 -26 1.29 1.47 0.55% 15 -27 1.31 1.49 0.67%
20 -26 1.43 1.67 0.83% 20 -26 1.45 1.70 0.83%

OXYGEN CONTENT 91% OXYGEN CONTENT 92%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

10 -28 1.19 1.30 0.48% 10 -29 1.20 1.32 0.48%

15 -28 1.32 1.51 0.67% 15 -28 1.34 1.54 0.67%
20 -27 1.46 1.72 0.83% 20 -28 1.48 1.74 0.83%

OXYGEN CONTENT 93% OXYGEN CONTENT 94%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

10 -29 1.21 1.34 0.55% 10 -30 1.22 1.36 0.55%

15 -29 1.35 1.56 0.67% 15 -29 1.37 1.58 0.67%
20 -28 1.49 1.77 0.83% 20 -29 1.51 1.79 2.22%

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – IMPERIAL (continued)

OXYGEN CONTENT 95% OXYGEN CONTENT 96%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -30 1.24 1.38 0.55% 10 -31 1.25 1.40 0.55%
15 -30 1.38 1.60 0.67% 15 -31 1.40 1.62 0.67%
20 -30 1.53 1.82 2.22% 20 -30 1.54 1.84 2.22%

OXYGEN CONTENT 97% OXYGEN CONTENT 98%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

10 -31 1.26 1.42 0.55% 10 -32 1.28 1.44 0.55%

15 -31 1.41 1.65 0.83% 15 -32 1.43 1.67 0.83%
20 -31 1.56 1.86 2.22% 20 -32 1.57 1.89 2.22%

OXYGEN CONTENT 99% OXYGEN CONTENT 100%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
10 -33 1.30 1.48 0.55%
10 -32 1.29 1.46 0.55%
15 -33 1.45 1.71 0.83%
15 -32 1.44 1.69 0.83%
20 -33 1.61 1.93 2.22%
20 -32 1.59 1.91 2.22%

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE
METRIC

OXYGEN CONTENT 21% OXYGEN CONTENT 22%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 2.8 0.29 –– 0.00%
3 3.0 0.27 –– 0.00%
5 4.8 0.33 –– 0.00%
5 5.0 0.32 –– 0.00%
6 5.8 0.35 –– 0.00%
6 6.0 0.34 –– 0.00%
9 8.8 0.42 –– 0.00%
9 9.0 0.40 –– 0.00%
12 11.7 0.48 –– 0.00%
12 12.0 0.46 –– 0.00%
15 14.7 0.55 0.15 0.14%
15 15.0 0.53 0.08 0.00%
18 17.6 0.62 0.30 0.17%
18 18.0 0.59 0.24 0.14%
21 20.6 0.68 0.43 0.17%
21 21.0 0.65 0.37 0.17%
24 23.6 0.75 0.56 0.22%
24 24.0 0.71 0.49 0.22%
27 26.5 0.81 0.68 0.28%
27 27.0 0.78 0.61 0.22%
30 29.5 0.88 0.80 0.28%
30 30.0 0.84 0.73 0.28%
33 32.5 0.95 0.91 0.33%
33 33.0 0.90 0.84 0.28%
36 35.4 1.01 1.02 0.42%
36 36.0 0.97 0.94 0.33%
39 38.4 1.08 1.13 0.42%
39 39.0 1.03 1.05 0.42%
42 41.3 1.14 1.23 0.48%
42 42.0 1.09 1.15 0.42%
45 44.3 1.21 1.34 0.55%
45 45.0 1.16 1.25 0.48%
48 47.3 1.28 1.44 0.55%
48 48.0 1.22 1.35 0.55%
51 50.2 1.34 1.54 0.67%
51 51.0 1.28 1.45 0.55%
54 53.2 1.41 1.64 0.83%
54 54.0 1.34 1.54 0.67%
57 56.2 1.47 1.74 0.83%
57 57.0 1.41 1.64 0.83%

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE
METRIC
OXYGEN CONTENT 23% OXYGEN CONTENT 24%
OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 2.7 0.30 –– 0.00% 3 2.5 0.31 –– 0.00%

5 4.6 0.35 –– 0.00% 5 4.4 0.36 –– 0.00%
6 5.6 0.37 –– 0.00% 6 5.4 0.38 –– 0.00%
9 8.5 0.44 –– 0.00% 9 8.3 0.46 –– 0.00%
12 11.4 0.51 0.03 0.14% 12 11.2 0.53 0.09 0.14%
15 14.4 0.58 0.21 0.14% 15 14.1 0.60 0.26 0.14%
18 17.3 0.64 0.36 0.17% 18 16.9 0.67 0.41 0.17%
21 20.2 0.71 0.49 0.22% 21 19.8 0.74 0.55 0.22%
24 23.1 0.78 0.62 0.22% 24 22.7 0.82 0.68 0.28%
27 26.1 0.85 0.75 0.28% 27 25.6 0.89 0.81 0.28%
30 29.0 0.92 0.87 0.33% 30 28.5 0.96 0.93 0.33%
33 31.9 0.99 0.98 0.33% 33 31.4 1.03 1.05 0.42%
36 34.8 1.06 1.10 0.42% 36 34.3 1.10 1.17 0.42%
39 37.8 1.13 1.21 0.48% 39 37.1 1.18 1.28 0.48%
42 40.7 1.20 1.32 0.48% 42 40.0 1.25 1.40 0.55%
45 43.6 1.27 1.42 0.55% 45 42.9 1.32 1.51 0.67%
48 46.5 1.33 1.53 0.67% 48 45.8 1.39 1.62 0.67%
51 49.5 1.40 1.63 0.67% 51 48.7 1.46 1.72 0.83%
54 52.4 1.47 1.74 0.83% 54 51.6 1.54 1.83 2.22%
57 55.3 1.54 1.84 2.22% 57 54.5 1.61 1.94 2.22%

282 Tec Deep Diver Manual

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – METRIC (continued)

OXYGEN CONTENT 25% OXYGEN CONTENT 26%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 2.3 0.33 –– 0.00% 3 2.2 0.34 –– 0.00%

5 4.2 0.38 –– 0.00% 5 4.1 0.39 –– 0.00%
6 5.2 0.40 –– 0.00% 6 5.0 0.42 –– 0.00%
9 8.0 0.48 –– 0.00% 9 7.8 0.49 –– 0.00%
12 10.9 0.55 0.15 0.14% 12 10.6 0.57 0.20 0.14%
15 13.7 0.63 0.32 0.17% 15 13.4 0.65 0.37 0.17%
18 16.6 0.70 0.47 0.17% 18 16.2 0.73 0.52 0.22%
21 19.4 0.78 0.61 0.22% 21 19.0 0.81 0.67 0.28%
24 22.3 0.85 0.74 0.28% 24 21.8 0.88 0.80 0.28%
27 25.1 0.93 0.87 0.33% 27 24.7 0.96 0.94 0.33%
30 28.0 1.00 1.00 0.33% 30 27.5 1.04 1.07 0.42%
33 30.8 1.08 1.12 0.42% 33 30.3 1.12 1.19 0.48%
36 33.7 1.15 1.24 0.48% 36 33.1 1.20 1.32 0.48%
39 36.5 1.23 1.36 0.55% 39 35.9 1.27 1.44 0.55%
42 39.4 1.30 1.48 0.55% 42 38.7 1.35 1.56 0.67%
45 42.2 1.38 1.59 0.67% 45 41.5 1.43 1.67 0.83%
48 45.1 1.45 1.70 0.83% 48 44.3 1.51 1.79 2.22%
51 47.9 1.53 1.81 2.22% 51 47.1 1.59 1.90 2.22%
54 50.8 1.60 1.92 2.22%

OXYGEN CONTENT 27% OXYGEN CONTENT 28%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 1.8 0.36 –– 0.00%
3 2.0 0.35 –– 0.00%
5 3.7 0.42 –– 0.00%
5 3.9 0.41 –– 0.00%
6 4.6 0.45 –– 0.00%
6 4.8 0.43 –– 0.00%
9 7.3 0.53 0.10 0.14%
9 7.6 0.51 0.05 0.14%
12 10.1 0.62 0.30 0.17%
12 10.3 0.59 0.25 0.14%
15 12.8 0.70 0.47 0.17%
15 13.1 0.68 0.42 0.17%
18 15.5 0.78 0.63 0.22%
18 15.9 0.76 0.57 0.22%
21 18.3 0.87 0.78 0.28%
21 18.6 0.84 0.72 0.28%
24 21.0 0.95 0.92 0.33%
24 21.4 0.92 0.86 0.33%
27 23.7 1.04 1.06 0.42%
27 24.2 1.00 1.00 0.33%
30 26.5 1.12 1.20 0.48%
30 27.0 1.08 1.13 0.42%
33 29.2 1.20 1.33 0.48%
33 29.7 1.16 1.26 0.48%
36 31.9 1.29 1.46 0.55%
36 32.5 1.24 1.39 0.55%
39 34.7 1.37 1.59 0.67%
39 35.3 1.32 1.51 0.67%
42 37.4 1.46 1.71 0.83%
42 38.1 1.40 1.63 0.67%
45 40.1 1.54 1.84 2.22%
45 40.8 1.49 1.76 0.83%
48 42.9 1.62 1.96 2.22%
48 43.6 1.57 1.87 2.22%
283

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – METRIC (continued)

OXYGEN CONTENT 29% OXYGEN CONTENT 30%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 1.7 0.38 –– 0.00%
3 1.5 0.39 –– 0.00%
5 3.5 0.44 –– 0.00%
5 3.3 0.45 –– 0.00%
6 4.4 0.46 –– 0.00%
6 4.2 0.48 –– 0.00%
9 7.1 0.55 0.15 0.14%
9 6.8 0.57 0.20 0.14%
12 9.8 0.64 0.34 0.17%
12 9.5 0.66 0.39 0.17%
15 12.5 0.73 0.52 0.22%
15 12.2 0.75 0.56 0.22%
18 15.2 0.81 0.68 0.28%
18 14.8 0.84 0.73 0.28%
21 17.9 0.90 0.83 0.28%
21 17.5 0.93 0.88 0.33%
24 20.6 0.99 0.98 0.33%
24 20.1 1.02 1.03 0.42%
27 23.3 1.07 1.12 0.42%
27 22.8 1.11 1.18 0.48%
30 25.9 1.16 1.26 0.48%
30 25.4 1.20 1.32 0.48%
33 28.6 1.25 1.40 0.55%
33 28.1 1.29 1.46 0.55%
36 31.3 1.33 1.53 0.67%
36 30.8 1.38 1.60 0.67%
39 34.0 1.42 1.66 0.83%
39 33.4 1.47 1.73 0.83%
42 36.7 1.51 1.79 2.22%
42 36.1 1.56 1.87 2.22%
45 39.4 1.60 1.92 2.22%

OXYGEN CONTENT 31% OXYGEN CONTENT 32%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 1.4 0.40 –– 0.00% 3 1.2 0.42 –– 0.00%
5 3.1 0.47 –– 0.00% 5 2.9 0.48 –– 0.00%
6 4.0 0.50 –– 0.00% 6 3.8 0.51 0.05 0.14%
9 6.6 0.59 0.24 0.14% 9 6.4 0.61 0.28 0.17%
12 9.2 0.68 0.43 0.17% 12 8.9 0.70 0.48 0.17%
15 11.8 0.78 0.61 0.22% 15 11.5 0.80 0.65 0.22%
18 14.5 0.87 0.78 0.28% 18 14.1 0.90 0.82 0.28%
21 17.1 0.96 0.93 0.33% 21 16.7 0.99 0.99 0.33%
24 19.7 1.05 1.09 0.42% 24 19.3 1.09 1.14 0.42%
27 22.3 1.15 1.24 0.48% 27 21.8 1.18 1.30 0.48%
30 24.9 1.24 1.38 0.55% 30 24.4 1.28 1.45 0.55%
33 27.6 1.33 1.53 0.67% 33 27.0 1.38 1.59 0.67%
36 30.2 1.43 1.67 0.83% 36 29.6 1.47 1.74 0.83%
39 32.8 1.52 1.81 2.22% 39 32.2 1.57 1.88 2.22%
42 35.4 1.61 1.94 2.22%

284 Tec Deep Diver Manual

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – METRIC (continued)

OXYGEN CONTENT 33% OXYGEN CONTENT 34%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 1.0 0.43 –– 0.00%
3 0.9 0.44 –– 0.00%
5 2.7 0.50 –– 0.00%
5 2.5 0.51 0.04 0.14%
6 3.6 0.53 0.09 0.14%
6 3.4 0.54 0.13 0.14%
9 6.1 0.63 0.32 0.17%
9 5.9 0.65 0.36 0.17%
12 8.7 0.73 0.52 0.22%
12 8.4 0.75 0.56 0.22%
15 11.2 0.83 0.70 0.28%
15 10.9 0.85 0.74 0.28%
18 13.7 0.92 0.87 0.33%
18 13.4 0.95 0.92 0.33%
21 16.3 1.02 1.04 0.42%
21 15.9 1.05 1.09 0.42%
24 18.8 1.12 1.20 0.48%
24 18.4 1.16 1.25 0.48%
27 21.4 1.22 1.36 0.55%
27 20.9 1.26 1.41 0.55%
30 23.9 1.32 1.51 0.67%
30 23.4 1.36 1.57 0.67%
33 26.5 1.42 1.66 0.83%
33 25.9 1.46 1.72 0.83%
36 29.0 1.52 1.80 2.22%
36 28.4 1.56 1.87 2.22%
39 31.6 1.62 1.95 2.22%

OXYGEN CONTENT 35% OXYGEN CONTENT 36%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 0.5 0.47 –– 0.00%
3 0.7 0.46 –– 0.00%
5 2.2 0.54 0.12 0.14%
5 2.3 0.53 0.08 0.14%
6 3.0 0.58 0.21 0.14%
6 3.2 0.56 0.17 0.14%
9 5.4 0.68 0.44 0.17%
9 5.6 0.67 0.40 0.17%
12 7.8 0.79 0.64 0.22%
12 8.1 0.77 0.60 0.22%
15 10.3 0.90 0.83 0.28%
15 10.6 0.88 0.79 0.28%
18 12.7 1.01 1.01 0.42%
18 13.0 0.98 0.97 0.33%
21 15.1 1.12 1.19 0.48%
21 15.5 1.09 1.14 0.42%
24 17.5 1.22 1.36 0.55%
24 18.0 1.19 1.31 0.48%
27 20.0 1.33 1.53 0.67%
27 20.4 1.30 1.47 0.55%
30 22.4 1.44 1.69 0.83%
30 22.9 1.40 1.63 0.67%
33 24.8 1.55 1.85 2.22%
33 25.4 1.51 1.79 2.22%
36 27.8 1.61 1.94 2.22%

Appendix 285

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – METRIC (continued)

OXYGEN CONTENT 37% OXYGEN CONTENT 38%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 0.4 0.48 –– 0.00% 3 0.2 0.49 –– 0.00%

5 2.0 0.56 0.16 0.14% 5 1.8 0.57 0.20 0.00%
6 2.8 0.59 0.25 0.14% 6 2.6 0.61 0.28 0.17%
9 5.2 0.70 0.47 0.17% 9 4.9 0.72 0.51 0.22%
12 7.5 0.81 0.68 0.28% 12 7.3 0.84 0.72 0.28%
15 9.9 0.93 0.87 0.33% 15 9.6 0.95 0.92 0.33%
18 12.3 1.04 1.06 0.42% 18 12.0 1.06 1.11 0.42%
21 14.7 1.15 1.24 0.48% 21 14.3 1.18 1.29 0.48%
24 17.1 1.26 1.41 0.55% 24 16.7 1.29 1.46 0.55%
27 19.5 1.37 1.58 0.67% 27 19.0 1.41 1.64 0.83%
30 21.9 1.48 1.75 0.83% 30 21.4 1.52 1.81 2.22%
33 24.3 1.59 1.91 2.22%

OXYGEN CONTENT 39% OXYGEN CONTENT 40%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 0.0 0.51 0.03 0.14% 3 -0.1 0.52 0.07 0.14%

5 1.6 0.59 0.23 0.14% 5 1.4 0.60 0.26 0.14%
6 2.4 0.62 0.31 0.17% 6 2.2 0.64 0.35 0.17%
9 4.7 0.74 0.55 0.22% 9 4.4 0.76 0.58 0.22%
12 7.0 0.86 0.76 0.28% 12 6.7 0.88 0.80 0.28%
15 9.3 0.98 0.96 0.33% 15 9.0 1.00 1.00 0.33%
18 11.6 1.09 1.15 0.42% 18 11.3 1.12 1.20 0.48%
21 13.9 1.21 1.34 0.55% 21 13.5 1.24 1.38 0.55%
24 16.3 1.33 1.52 0.67% 24 15.8 1.36 1.57 0.67%
27 18.6 1.44 1.69 0.83% 27 18.1 1.48 1.75 0.83%
30 20.9 1.56 1.87 2.22% 30 20.4 1.60 1.92 2.22%

286 Tec Deep Diver Manual

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – METRIC (continued)

OXYGEN CONTENT 41% OXYGEN CONTENT 42%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -0.3 0.53 0.10 0.14% 3 -0.5 0.55 0.14 0.14%

5 1.2 0.62 0.30 0.17% 5 1.0 0.63 0.33 0.17%
6 1.9 0.66 0.38 0.17% 6 1.7 0.67 0.41 0.17%
9 4.2 0.78 0.62 0.22% 9 3.9 0.80 0.65 0.22%
12 6.4 0.90 0.83 0.28% 12 6.2 0.92 0.87 0.33%
15 8.7 1.03 1.04 0.42% 15 8.4 1.05 1.08 0.42%
18 10.9 1.15 1.24 0.48% 18 10.6 1.18 1.28 0.48%
21 13.2 1.27 1.43 0.55% 21 12.8 1.30 1.48 0.55%
24 15.4 1.39 1.62 0.67% 24 15.0 1.43 1.67 0.83%
27 17.6 1.52 1.80 2.22% 27 17.2 1.55 1.86 2.22%

OXYGEN CONTENT 43% OXYGEN CONTENT 44%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -0.6 0.56 0.17 0.14% 3 -0.8 0.57 0.20 0.14%

5 0.8 0.65 0.36 0.17% 5 0.6 0.66 0.39 0.17%
6 1.5 0.69 0.44 0.17% 6 1.3 0.70 0.48 0.17%
9 3.7 0.82 0.69 0.28% 9 3.5 0.84 0.72 0.28%
12 5.9 0.95 0.91 0.33% 12 5.6 0.97 0.95 0.33%
15 8.0 1.08 1.12 0.42% 15 7.7 1.10 1.16 0.42%
18 10.2 1.20 1.33 0.48% 18 9.8 1.23 1.37 0.55%
21 12.4 1.33 1.53 0.55% 21 12.0 1.36 1.57 0.67%
24 14.5 1.46 1.72 0.83% 24 14.1 1.50 1.77 0.83%
27 16.7 1.59 1.91 2.22%

OXYGEN CONTENT 45% OXYGEN CONTENT 46%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -0.9 0.59 0.23 0.14% 3 -1.1 0.60 0.26 0.14%

5 0.4 0.68 0.42 0.17% 5 0.3 0.69 0.45 0.17%
6 1.1 0.72 0.51 0.22% 6 0.9 0.74 0.54 0.22%
9 3.2 0.86 0.75 0.28% 9 3.0 0.87 0.79 0.28%
12 5.3 0.99 0.98 0.33% 12 5.0 1.01 1.02 0.42%
15 7.4 1.13 1.20 0.48% 15 7.1 1.15 1.24 0.48%
18 9.5 1.26 1.42 0.55% 18 9.1 1.29 1.46 0.55%
21 11.6 1.40 1.62 0.67% 21 11.2 1.43 1.67 0.83%
24 13.7 1.53 1.82 2.22% 24 13.2 1.56 1.87 2.22%

Appendix 287

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – METRIC (continued)

OXYGEN CONTENT 47% OXYGEN CONTENT 48%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -1.3 0.61 0.29 0.17%
3 -1.4 0.62 0.31 0.17%
5 0.1 0.71 0.48 0.22%
5 -0.1 0.72 0.51 0.22%
6 0.7 0.75 0.57 0.22%
6 0.5 0.77 0.60 0.22%
9 2.7 0.89 0.82 0.28%
9 2.5 0.91 0.85 0.33%
12 4.8 1.03 1.06 0.42%
12 4.5 1.06 1.09 0.42%
15 6.8 1.18 1.28 0.48%
15 6.5 1.20 1.32 0.48%
18 8.8 1.32 1.50 0.67%
18 8.4 1.34 1.54 0.67%
21 10.8 1.46 1.71 0.83%
21 10.4 1.49 1.76 0.83%
24 12.8 1.60 1.92 2.22%

OXYGEN CONTENT 49% OXYGEN CONTENT 50%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -1.6 0.64 0.34 0.17% 3 -1.8 0.65 0.37 0.17%

5 -0.3 0.74 0.53 0.22% 5 -0.5 0.75 0.56 0.22%
6 0.3 0.78 0.63 0.22% 6 0.1 0.80 0.65 0.22%
9 2.3 0.93 0.88 0.33% 9 2.0 0.95 0.92 0.33%
12 4.2 1.08 1.13 0.42% 12 3.9 1.10 1.16 0.42%
15 6.1 1.23 1.36 0.55% 15 5.8 1.25 1.40 0.55%
18 8.1 1.37 1.59 0.67% 18 7.7 1.40 1.63 0.67%
21 10.0 1.52 1.81 2.22% 21 9.6 1.55 1.85 2.22%

OXYGEN CONTENT 51% OXYGEN CONTENT 52%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -1.9 0.66 0.39 0.17% 3 -2.1 0.68 0.42 0.17%
5 -0.7 0.77 0.59 0.22% 5 -0.9 0.78 0.62 0.22%
6 -0.1 0.82 0.68 0.28% 6 -0.3 0.83 0.71 0.28%
9 1.8 0.97 0.95 0.33% 9 1.5 0.99 0.98 0.33%
12 3.6 1.12 1.20 0.48% 12 3.4 1.14 1.23 0.48%
15 5.5 1.28 1.44 0.55% 15 5.2 1.30 1.48 0.55%
18 7.4 1.43 1.67 0.83% 18 7.0 1.46 1.71 0.83%
21 9.2 1.58 1.90 2.22% 21 8.8 1.61 1.94 2.22%

288 Tec Deep Diver Manual

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – METRIC (continued)

OXYGEN CONTENT 53% OXYGEN CONTENT 54%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -2.3 0.69 0.45 0.17% 3 -2.4 0.70 0.47 0.17%

5 -1.1 0.80 0.65 0.22% 5 -1.3 0.81 0.67 0.28%
6 -0.5 0.85 0.74 0.28% 6 -0.7 0.86 0.77 0.28%
9 1.3 1.01 1.01 0.42% 9 1.1 1.03 1.04 0.42%
12 3.1 1.17 1.27 0.48% 12 2.8 1.19 1.30 0.48%
15 4.9 1.33 1.52 0.67% 15 4.6 1.35 1.55 0.67%
18 6.7 1.48 1.75 0.83% 18 6.3 1.51 1.80 2.22%

OXYGEN CONTENT 55% OXYGEN CONTENT 56%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -2.6 0.72 0.50 0.22% 3 -2.8 0.73 0.52 0.22%

5 -1.5 0.83 0.70 0.28% 5 -1.6 0.84 0.73 0.28%
6 -0.9 0.88 0.80 0.28% 6 -1.1 0.90 0.82 0.28%
9 0.8 1.05 1.07 0.42% 9 0.6 1.06 1.11 0.42%
12 2.5 1.21 1.34 0.55% 12 2.3 1.23 1.37 0.55%
15 4.2 1.38 1.59 0.67% 15 3.9 1.40 1.63 0.67%
18 5.9 1.54 1.84 2.22% 18 5.6 1.57 1.88 2.22%

OXYGEN CONTENT 57% OXYGEN CONTENT 58%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -3.1 0.75 0.57 0.22%
3 -2.9 0.74 0.55 0.22%
5 -2.0 0.87 0.78 0.28%
5 -1.8 0.86 0.75 0.28%
6 -1.5 0.93 0.88 0.33%
6 -1.3 0.91 0.85 0.33%
9 0.1 1.10 1.17 0.42%
9 0.3 1.08 1.14 0.42%
12 1.7 1.28 1.44 0.55%
12 2.0 1.25 1.41 0.55%
15 3.3 1.45 1.70 0.83%
15 3.6 1.43 1.67 0.83%
18 4.9 1.62 1.96 2.22%
18 5.2 1.60 1.92 2.22%

Appendix 289

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – METRIC (continued)

OXYGEN CONTENT 59% OXYGEN CONTENT 60%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -3.3 0.77 0.59 0.22% 3 -3.4 0.78 0.62 0.22%
5 -2.2 0.89 0.80 0.28% 5 -2.4 0.90 0.83 0.28%
6 -1.7 0.94 0.91 0.33% 6 -1.9 0.96 0.93 0.33%
9 -0.1 1.12 1.20 0.48% 9 -0.4 1.14 1.23 0.48%
12 1.4 1.30 1.47 0.55% 12 1.1 1.32 1.51 0.67%
15 3.0 1.48 1.74 0.83% 15 2.7 1.50 1.78 0.83%

OXYGEN CONTENT 61% OXYGEN CONTENT 62%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -3.7 0.81 0.67 0.28%
3 -3.6 0.79 0.64 0.22%
5 -2.8 0.93 0.88 0.33%
5 -2.6 0.92 0.86 0.33%
6 -2.3 0.99 0.99 0.33%
6 -2.1 0.98 0.96 0.33%
9 -0.9 1.18 1.29 0.48%
9 -0.6 1.16 1.26 0.48%
12 0.6 1.36 1.57 0.67%
12 0.9 1.34 1.54 0.67%
15 2.0 1.55 1.85 2.22%
15 2.3 1.53 1.81 2.22%

OXYGEN CONTENT 63% OXYGEN CONTENT 64%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -3.9 0.82 0.69 0.28%
3 -4.1 0.83 0.71 0.28%
5 -3.0 0.95 0.91 0.33%
5 -3.2 0.96 0.93 0.33%
6 -2.5 1.01 1.01 0.42%
6 -2.7 1.02 1.04 0.42%
9 -1.1 1.20 1.32 0.48%
9 -1.3 1.22 1.35 0.55%
12 0.3 1.39 1.61 0.67%
12 0.0 1.41 1.64 0.83%
15 1.7 1.58 1.89 2.22%
15 1.4 1.60 1.92 2.22%

OXYGEN CONTENT 65% OXYGEN CONTENT 66%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -4.2 0.85 0.73 0.28% 3 -4.4 0.86 0.76 0.28%

5 -3.4 0.98 0.96 0.33% 5 -3.5 0.99 0.98 0.33%
6 -2.9 1.04 1.07 0.42% 6 -3.1 1.06 1.09 0.42%
9 -1.6 1.24 1.38 0.55% 9 -1.8 1.25 1.41 0.55%
12 -0.3 1.43 1.67 0.83% 12 -0.5 1.45 1.71 0.83%

290 Tec Deep Diver Manual

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – METRIC (continued)

OXYGEN CONTENT 67% OXYGEN CONTENT 68%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -4.6 0.87 0.78 0.28% 3 -4.7 0.88 0.80 0.28%

5 -3.7 1.01 1.01 0.42% 5 -3.9 1.02 1.03 0.42%
6 -3.3 1.07 1.12 0.42% 6 -3.5 1.09 1.14 0.42%
9 -2.1 1.27 1.44 0.55% 9 -2.3 1.29 1.46 0.55%
12 -0.8 1.47 1.74 0.83% 12 -1.1 1.50 1.77 0.83%

OXYGEN CONTENT 69% OXYGEN CONTENT 70%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -4.9 0.90 0.83 0.28% 3 -5.1 0.91 0.85 0.33%

5 -4.1 1.04 1.06 0.42% 5 -4.3 1.05 1.08 0.42%
6 -3.7 1.10 1.17 0.42% 6 -3.9 1.12 1.20 0.48%
9 -2.5 1.31 1.49 0.67% 9 -2.8 1.33 1.52 0.67%
12 -1.4 1.52 1.80 2.22% 12 -1.6 1.54 1.84 2.22%

OXYGEN CONTENT 71% OXYGEN CONTENT 72%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -5.2 0.92 0.87 0.33% 3 -5.4 0.94 0.89 0.33%

5 -4.5 1.07 1.11 0.42% 5 -4.7 1.08 1.13 0.42%
6 -4.1 1.14 1.22 0.48% 6 -4.3 1.15 1.25 0.48%
9 -3.0 1.35 1.55 0.67% 9 -3.3 1.37 1.58 0.67%
12 -1.9 1.56 1.87 2.22% 12 -2.2 1.58 1.90 2.22%

OXYGEN CONTENT 73% OXYGEN CONTENT 74%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -5.6 0.95 0.91 0.33% 3 -5.7 0.96 0.94 0.33%

5 -4.9 1.10 1.16 0.42% 5 -5.1 1.11 1.18 0.48%
6 -4.5 1.17 1.27 0.48% 6 -4.7 1.18 1.30 0.48%
9 -3.5 1.39 1.61 0.67% 9 -3.7 1.41 1.64 0.83%
12 -2.5 1.61 1.93 2.22%

Appendix 291

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – METRIC (continued)

OXYGEN CONTENT 75% OXYGEN CONTENT 76%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -5.9 0.98 0.96 0.33% 3 -6.1 0.99 0.98 0.33%

5 -5.3 1.13 1.20 0.48% 5 -5.4 1.14 1.23 0.48%
6 -4.9 1.20 1.32 0.48% 6 -5.1 1.22 1.35 0.55%
9 -4.0 1.43 1.67 0.83% 9 -4.2 1.44 1.69 0.83%

OXYGEN CONTENT 77% OXYGEN CONTENT 78%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -6.2 1.00 1.00 0.33%
3 -6.4 1.01 1.02 0.42%
5 -5.6 1.16 1.25 0.48%
5 -5.8 1.17 1.27 0.48%
6 -5.3 1.23 1.37 0.55%
6 -5.5 1.25 1.40 0.55%
9 -4.5 1.46 1.72 0.83%
9 -4.7 1.48 1.75 0.83%

OXYGEN CONTENT 79% OXYGEN CONTENT 80%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -6.5 1.03 1.04 0.42% 3 -6.7 1.04 1.07 0.42%
5 -6.0 1.19 1.30 0.48% 5 -6.2 1.20 1.32 0.48%
6 -5.7 1.26 1.42 0.55% 6 -5.9 1.28 1.45 0.55%
9 -4.9 1.50 1.78 0.83% 9 -5.2 1.52 1.81 2.22%

OXYGEN CONTENT 81% OXYGEN CONTENT 82%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -6.9 1.05 1.09 0.42% 3 -7.0 1.07 1.11 0.42%
5 -6.4 1.22 1.35 0.55% 5 -6.6 1.23 1.37 0.55%
6 -6.2 1.30 1.47 0.55% 6 -6.4 1.31 1.50 0.67%
9 -5.4 1.54 1.84 2.22% 9 -5.7 1.56 1.86 2.22%

OXYGEN CONTENT 83% OXYGEN CONTENT 84%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -7.2 1.08 1.13 0.42%
3 -7.4 1.09 1.15 0.42%
5 -6.8 1.25 1.39 0.55%
5 -7.0 1.26 1.42 0.55%
6 -6.6 1.33 1.52 0.67%
6 -6.8 1.34 1.54 0.67%
9 -5.9 1.58 1.89 2.22%
9 -6.2 1.60 1.92 2.22%

292 Tec Deep Diver Manual

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – METRIC (continued)

OXYGEN CONTENT 85% OXYGEN CONTENT 86%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -7.5 1.11 1.17 0.48%
3 -7.7 1.12 1.19 0.48%
5 -7.2 1.28 1.44 0.55%
5 -7.3 1.29 1.46 0.55%
6 -7.0 1.36 1.57 0.67%
6 -7.2 1.38 1.59 0.67%
9 -6.4 1.62 1.95 2.22%

OXYGEN CONTENT 87% OXYGEN CONTENT 88%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -7.9 1.13 1.21 0.48% 3 -8.0 1.14 1.23 0.48%

5 -7.5 1.31 1.48 0.67% 5 -7.7 1.32 1.51 0.67%
6 -7.4 1.39 1.62 0.67% 6 -7.6 1.41 1.64 0.83%

OXYGEN CONTENT 89% OXYGEN CONTENT 90%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -8.2 1.16 1.25 0.48% 3 -8.4 1.17 1.27 0.48%

5 -7.9 1.34 1.53 0.67% 5 -8.1 1.35 1.55 0.67%
6 -7.8 1.42 1.66 0.83% 6 -8.0 1.44 1.69 0.83%

OXYGEN CONTENT 91% OXYGEN CONTENT 92%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -8.5 1.18 1.30 0.48%
3 -8.7 1.20 1.32 0.48%
5 -8.3 1.37 1.58 0.67%
5 -8.5 1.38 1.60 0.67%
6 -8.2 1.46 1.71 0.83%
6 -8.4 1.47 1.74 0.83%

OXYGEN CONTENT 93% OXYGEN CONTENT 94%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -8.8 1.21 1.34 0.55% 3 -9.0 1.22 1.36 0.55%
5 -8.7 1.40 1.62 0.67% 5 -8.9 1.41 1.64 0.83%
6 -8.6 1.49 1.76 0.83% 6 -8.8 1.50 1.78 0.83%

Appendix 293

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 EQUIVALENT AIR DEPTH AND OXYGEN MANAGEMENT TABLE – METRIC (continued)

OXYGEN CONTENT 95% OXYGEN CONTENT 96%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min

3 -9.2 1.24 1.38 0.55% 3 -9.3 1.25 1.40 0.55%

5 -9.1 1.43 1.67 0.83% 5 -9.2 1.44 1.69 0.83%
6 -9.0 1.52 1.81 2.22% 6 -9.2 1.54 1.83 2.22%

OXYGEN CONTENT 97% OXYGEN CONTENT 98%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -9.5 1.26 1.42 0.55% 3 -9.7 1.27 1.44 0.55%
5 -9.4 1.46 1.71 0.83% 5 -9.6 1.47 1.73 0.83%
6 -9.4 1.55 1.85 2.22% 6 -9.6 1.57 1.88 2.22%

OXYGEN CONTENT 99% OXYGEN CONTENT 100%

OTU / CNS% OTU / CNS%
Depth EAD PO2 Min Min Depth EAD PO2 Min Min
3 -9.8 1.29 1.46 0.55%
3 -10.0 1.30 1.48 0.55%
5 -9.8 1.49 1.76 0.83
5 -10.0 1.50 1.78 0.83%
6 -9.8 1.58 1.90 2.22%
6 -10.0 1.60 1.92 2.22%

294 Tec Deep Diver Manual

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 Tec Deep Diver Statement of Understanding and Learning Agreement
This statement informs you of hazards, risks and your responsibilities for participating in the DSAT Tec Deep Diver course. Your signature
acknowledges that you accept these risks and responsibilities.

I, ___________________________________________________, understand that as a DSAT Tec Deep Diver (or Apprentice Tec Diver) I should:

1. Maintain good mental and physical health for diving. Refrain 8. Obtain an orientation when diving in new environments.
from being under the influence of alcohol or drugs when
9. Know, obey and respect local diving laws and regulations
tec diving. Stay proficient in diving skills, in particular, the
including private land owner relations.
skills required for certification as a DSAT Tec Deep Diver (or
Apprentice Tec Diver). 10. Accept the responsibility for my personal safety, while accepting
and acknowledging the risks, and demands tec diving imposes.
2. Engage only in diving activities consistent with my training
and experience. 11. Stay informed on and dive according to the state of the art in
diving, tec diving, dive rescue, dive equipment and other influ-
3. Use complete, well-maintained, reliable equipment for
ences on my safety as a tec diver.
which I have appropriate training.
12. Accept that technical scuba diving has many general risks and
4. Adhere to the team diving concept, but always be prepared
hazards that either don’t exist in recreational diving, or aren’t as
to complete any dive without the assistance of a team mate.
severe, including:
Although self sufficient, the responsible tec diver dives as
• No direct access to the surface in an emergency due to
part of a team and adheres to team diving principles.
decompression requirements.
5. Maintain the proper attitude during training in which I
• Hypoxia/hyperoxia resulting from switching to the wrong gas,
agree to:
which can lead to drowning.
• Follow the instructor’s directions and dive plans strictly,
and not to separate from the instructor or my dive team. • Narcosis, which can lead to poor judgment/bad decisions that
can cause an accident.
• Refrain from tec diving outside this course until I am fully
qualified and certified. • DCS due to improper gas analysis, missed deco stops, loss of
deco gas and individual susceptibility. DCS can cause perma-
• Accept the risk for this type of diving, and for specific risks
nent injury or death.
unique to each dive environment, and to immediately
notify the instructor if this risk becomes intolerable for me. • Omitted procedures due to task loading, which can lead to
accidents, DCS, air embolism, oxygen toxicity, or drowning.
• Recognize the desirability of carrying diver accident insur-
ance that covers tec diving (if available in my local area), • Drowning or air embolism due to BCD failure.
and recognize that my instructor may require me to have • Extensive equipment requirements with redundant configura-
it. tions, which can lead to ergonomic complexity, increased risk
6. Demonstrate self sufficiency – plan each dive as though it of error and a physical burden.
will be necessary to make the dive and handle all emergen- 13. I accept that a significant difference exists between recreational
cies alone. scuba diving and technical scuba diving, and that in technical
7. Demonstrate discipline and an attitude consistent with scuba diving, even if you do everything right, there is still a
responsible technical diving – I will not cut corners, bend higher inherent potential for an accident leading to permanent
the rules, disregard dive plans, omit safety equipment or injury or death.
exceed the limits of my training.
I have read the above statements and have had any questions answered to my satisfaction. I understand the importance and purpose of
these practices and recognize they are for my own safety and well being.
I understand that failing to ahere to the above statements will put me at risk, and may be grounds for my dismissal from the Tec Deep
Diver course. I acknowledge that the instructor is not permitted to and will not certify me if I don’t meet all course performance require-
ments or if I demonstrate an attitude or behavior incompatible with responsible technical diving practices.
____________________________________________________________ ______________________
Participant Signature Day/Month/Year

Appendix 295

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