1

GAS TESTING &

MONITORING
OBJECTIVES

The objectives of this presentation are:

• To identify the causes of hazardous atmospheres.

• To review the principles of gas testing.

Prepared By | Safety Professional | www.safetygoodwe.com 2

 Contents

Why Carry out a Gas Test

What Defines A Safe Atmosphere
Properties of Flammable, Explosive and Toxic Gases and Vapours
Properties, Effects and Symptoms of Hydrogen Sulphide
Control of Substance Hazardous to Health
Density of Gases and Vapors
Characteristics of Gas
Application and types of Portable Gas Detectors and Operation

Prepared By | Safety Professional | www.safetygoodwe.com 3

Introduction

Gas testing must be

Many fatalities have
completed by trained
occurred because gas
competent personnel.
testing had not been
However, it is important
conducted or the tests
that everyone understands
have been inadequate.
the basic requirements.

Prepared By | Safety Professional | www.safetygoodwe.com 4

Categories
In the oil/gas and petrochemical industries, gas hazards are of particular importance. These hazards can be
split into 3 main categories

• The first are oxygen hazards, in the air we breathe if there’s too much or not enough oxygen you or
your work mates may die.

• Secondly explosive gases and flammable vapours, which, when mixed with air in certain proportions
can lead to fires or explosions.

• And finally harmful or toxic gas hazards; these cover everything from inert gases like nitrogen, used in
purging operations, which, simply displace the oxygen out of the air we are breathing, right through
to the nerve gases like Hydrogen Sulphide, which chemically interfere with the cells in our body.

Each one of these hazards are serious and life threatening.

Prepared By | Safety Professional | www.safetygoodwe.com 5

Type of Gas
Detector

Prepared By | Safety Professional | www.safetygoodwe.com 6

The following abbreviations are used:

CH4-
AGT- H2S-
Methane (a
Authorized Gas Hydrogen Sulphide
flammable
Tester. (a toxic gas).
hydrocarbon gas).

LEL- UEL-
PPM-
Lower Explosive Upper Explosive
Parts Per Million.
Limit. Limit.

Prepared By | Safety Professional | www.safetygoodwe.com 7

 The
Combustion
Triangle
 • Before entering a confined space or
To prevent an vessel
incident 3 main
types of gas • Before undertaking any type of hot-
work
testing are
undertaken: • During inserting

Prepared By | Safety Professional | www.safetygoodwe.com 9

 • Gas - any substance of very low density
The following and viscosity. ( No shape, fills the free
space of container)
definitions are
• Vapor - mist or fumes suspended in air.
used in this
• Liquid- any flowing substance with
presentation: little tendency to disperse. ( No
shape, takes shape of container)

Prepared By | Safety Professional | www.safetygoodwe.com 10

Gas testing is involved with the following activities:
Hot work of any type where heat is used or generated,
e.g.. by welding, flame cutting and grinding, etc.

Work which may generate sparks or other sources of

ignition.

Work which may cause an uncontrolled release of

hydrocarbons, other flammable or toxic materials.

Electrical instrumentation work which may cause

sparks

Entry into confined spaces and Gas alarm investigation

Prepared By | Safety Professional | www.safetygoodwe.com 11
WHY CARRY OUT A GAS CHECK?
Confined Space and Vessel Entry Gas Testing

01 02 03 04
OXYGEN OXYGEN GAS OR TOXIC GAS …
DEFICIENCY … ENRICHMENT … FLAMMABLE POISONING
SUFFOCATION / FIRE / EXPLOSION VAPOUR …FIRE OR HAZARD
DEATH HAZARD EXPLOSIVE
HAZARD

Prepared By | Safety Professional | www.safetygoodwe.com 12

To certify that the
atmosphere within a
confined space is free
from Flammable,
Explosive or Toxic
substances and that the
Oxygen content is 20.9%
IN OTHER WORDS, TO CERTIFY
THAT THE ATMOSPHERE IS SAFE
TO WORK IN!

Prepared By | Safety Professional | www.safetygoodwe.com 13

WHY CARRY OUT
A GAS CHECK?
Hot Work Gas Testing

To certify that there are no leaks

or accumulations of Flammable
Vapours or Explosive gases at the
worksite when Hot work is being
under taken

Prepared By | Safety Professional | www.safetygoodwe.com 14

WHAT DEFINES A SAFE ATMOSPHERE?

Looking at all the essential needs

of our body, sufficient oxygen is
the most urgent, immediate and
basic need we have. Without
sufficient oxygen we will lose
consciousness quickly and die in a
few Minutes.

THE CORRECT FIGURES FOR

OXYGEN IS 20.9%, BELOW OR
ABOVE THIS FIGURE IS
POTENTIALLY HAZARDOUS.

Prepared By | Safety Professional | www.safetygoodwe.com 15

LOW OXYGEN EFFECT AND SYMPTOMS

15 to 19% Strenuous work is difficult

12 to 14% Respiration and pulse increases,

co-ordination and judgment impaired
9 to 11% Nausea, fainting, blue lips,
unconsciousness
6 to 8% Death within 8 minutes, recovery if
resuscitated within 4 minutes

Remember! that rusting of steelwork and some

chemicals in confined spaces can reduce the oxygen in
the atmosphere to dangerous levels very quickly.

Prepared By | Safety Professional | www.safetygoodwe.com 16

HIGH OXYGEN EFFECTS AND SYMPTOMS
Above 23% oxygen serious fire risk causing some materials to
spontaneously combust, for example oily cloth and steel wool >(30%)

Prolonged exposure causes damage to breathing processes and an

intoxication which seriously disturbs judgment with (industrial 02 gas)

Most gas detection apparatus is uncertified if the oxygen content is

increased above atmosphere levels

Note: The minimum content of Oxygen required for a Catalytic Gas

detector reading LEL, is 13% or more to read accurately.

Prepared By | Safety Professional | www.safetygoodwe.com 17

 PROPERTIES OF EXPLOSIVE GASES AND
FLAMMABLE VAPOURS

All combustible gases and vapors are characterized by explosive limits between which,
the gas or vapor mixed with air is capable of sustaining the spread of flame. These can
be referred to as the Explosive or Flammable limits

Prepared By | Safety Professional | www.safetygoodwe.com 18

 The Lower Explosive Limit (LEL) of methane is 5% The Upper Explosive Limit ( UEL ) refers to the
by volume i.e. 5 volumes of methane mixed with highest concentration of a gas in the atmosphere
95 volumes of air. This is the minimum quantity of which results in a combustible mixture. For
Methane in a methane/air mixture that will ignite example, the UEL of Methane in air is 15% by
to produce a self propagating flame if exposed to volume, which means that if there is more than
a hot source or a spark from electrical or 15% of Methane in the air by volume the mixture
mechanical equipment. if there is less than 5% of is too rich to support combustion.
Methane in the air by volume the mixture is too
lean to support combustion.

SUBSTANCE LEL UEL

(Vol%) (Vol%)
ACETONE 2.15 13
ACETYLENE 2.4 88
Explosive BUTANE 1.5 8.5
ranges of ETHANE 3 15.5
ETHYLENE 2.7 34
other gases HEXANE 1.2 7.4
HYDROGEN 4 75.6
METHANE 5 15
Prepared By | Safety Professional | www.safetygoodwe.com PROPANE 2 9.5 19
For example, our list of L.E.L.s shows that Methane has an L.E.L. of 5.0%. This means that a
mixture of 5.0% Methane and 95.0% air, equals 100%, the

L.E.L. for Methane

Prepared By | Safety Professional | www.safetygoodwe.com 20

The most important point to remember is that any indication between 5 – 10% LEL on
the detector means caution and possible danger

Prepared By | Safety Professional | www.safetygoodwe.com 21

 Properties of Harmful & Toxic Gases

Within the oil and gas industry a wide range of harmful and toxic gases
can be encountered generally they can be sub-divided into Asphyxiant
and Toxic Gases.

ASPHYXIANT GASES:

• Simple displacement of oxygen from the air we breathe by any

one of these gases can lead to suffocation, remember nitrogen is
widely used in purging applications.

• This heightens the importance of the oxygen gas test at the

entrance to any confined space, remember 20.9% oxygen is the
correct figure.

Prepared By | Safety Professional | www.safetygoodwe.com 22

TOXIC GASES
Toxic gases chemically interfere with the vital processes taking place within our
bodies, only minute amounts of these gases need to be present in our breathing
air to cause catastrophic effects..

As the amount needed to poison us, is well below 1% in quantity, the expression
‘parts per million’ is used to measure these very small quantities of gas.
• examples:
• 10 ppm is the same as 0.001%
• 100 ppm is the same as 0.01%
• 1000 ppm is the same as 0.1%
• 10,000 ppm is the same as 1%
Prepared By | Safety Professional | www.safetygoodwe.com
23
PROPERTIES OF HARMFUL AND TOXIC GASES YOU MAY COME ACROSS

GAS Application And Were Found

Condensate or heavy Hydrocarbon vapours Crude oil residues, oil condensate and Sludges

Hydrogen Sulphide Reservoir gas, crude oil vapour and stagnant water.

Carbon Monoxide Associated with combustion process.

Carbon Dioxide Fire extinguishers and Deluge systems

Sulphur Dioxide Sulphur recovery plants and Flare stacks

Chlorine Water treatment

Benzene Sometimes found in crude oil and vapours.

Trichloroethane Solvent sometimes used in de-greasing fluids and dye- penetrants.

Prepared By | Safety Professional | www.safetygoodwe.com 24
PROPERTIES OF HARMFUL AND TOXIC GASES YOU MAY
COME ACROSS
GAS APPLICATION AND WHERE FOUND.

Sulphur Dioxide Sulphur recovery plants and Flare

stacks.

Chlorine Water treatment.

Benzene Sometimes found in crude oil and

vapours.

Trichloroethane Solvent sometimes used in de-greasing

fluids and dye- penetrants.

Prepared By | Safety Professional | www.safetygoodwe.com 25

Prepared By | Safety Professional | www.safetygoodwe.com 26
 27

Hydrogen Sulphide is found widely in

the oil industry, it is found in crude oil,
it is found in some natural gases and it
PROPERTIES OF can even be found in stagnant water,
particularly sea water.
HYDROGEN
SULPHIDE Hydrogen Sulphide is a ‘nerve gas ; its
almost as toxic as cyanide and whilst at
very low concentrations it is not
considered to be harmful to us, at high
concentrations it is lethal.

Prepared By | Safety Professional | www.safetygoodwe.com

HYDROGEN SULPHIDE
gas is referred to by a
variety of names:

• Sour gas
• Rotten egg gas
• Sulphurated Hydrogen
• H2S

Prepared By | Safety Professional | www.safetygoodwe.com 28

MAIN CHARACTERISTICS OF H2S:
• Potentially lethal.

• Colourless.

• Heavier than air.

• Readily dispersed by wind or air currents.

• Flammable - burns with a blue flame.

• Odour of rotten eggs (below concentration of 100 ppm).

• Highly corrosive to certain materials (eg. steel).

Prepared By | Safety Professional | www.safetygoodwe.com 29

EFFECT OF H2S ON PERSONNEL
The way in which H2S affects you depends on the following:

• Duration: the length of time the individual is

exposed.

Frequency: how often the individual has been

exposed.

Intensity: the concentration of exposure.

Susceptibility: the individual’s physiological make up.

Prepared By | Safety Professional | www.safetygoodwe.com 30
EFFECT OF H2S ON PERSONNEL
0.0025 ppm Minimum concentration which produces
odour

10 - 20 ppm Eye and respiratory tract irritation,

especially in vulnerable workers.

20 - 100 ppm Inflammation, blistering and opacity of the

eye, loss of the sense of smell, headache,
cough and nausea.

100 - 300 ppm Respiratory difficulty, respiratory depression and

irritation (exposures of 30 minutes to 8 hours).
Prepared By | Safety Professional | www.safetygoodwe.com 31
 EFFECTS AND SYMPTEMS OF H2S

0.0025 ppm Minimum concentration which produces

odour

10 - 20 ppm Eye and respiratory tract irritation,

especially in vulnerable workers.

20 - 100 ppm Inflammation, blistering and opacity of the

eye, loss of the sense of smell, headache,
cough and nausea.

100 - 300 ppm Respiratory difficulty, respiratory depression

and irritation (exposures of 30 minutes to 8
hours).

Prepared By | Safety Professional | www.safetygoodwe.com 32

 EFFECTS AND SYMPTEMS OF H2S

300 - 700 ppm Central nervous system effects , eg

tremors, weakness, numbness of
extremities, unconsciousness and
convulsions.

700 - 1000 ppm Rapid (one to several breaths will result

in unconsciousness)

Above 1000 ppm Cessation of breathing (instantaneous)

followed by death.

Prepared By | Safety Professional | www.safetygoodwe.com 33

 Effect of H2S on personnel

If a person inhales H2S, it passes directly through the

lungs in to the bloodstream. To protect itself, the body
’oxidises’ (breaks down) the gas as rapidly as possible
into a harmless compound.

If the person breathes in too much H2S, the body cannot

oxsidise all of it, it builds up in the blood and the person
becomes poisoned. The areas of the brain which control
breathing become paralysed, the lungs stop working and
the person is asphyxiated.

Prepared By | Safety Professional | www.safetygoodwe.com 34

 REMEMBER!
700ppm sounds a lot, but
it is only 0.07% vol.,
There may well be
99.93% vol. of fresh air
as the remainder.
Prepared By | Safety Professional | www.safetygoodwe.com 35
EXPOSURE LIMITS AND THE COSHH REGULATIONS

The maximum amount of any toxic gas

that you’re allowed to be exposed to in
the workplace is controlled by law.

The Control Of Substances Hazardous to

Health in the UK or COSHH which states
how much of a particular toxic material
you are allowed to be exposed too and
for how long.

Prepared By | Safety Professional | www.safetygoodwe.com 36

 DENSITY OF GASES AND VAPOURS

1.Relative Density of Pure Gas

Gases when pure and concentrated are

either lighter than air, neutral in density
or heavier than air. To simplify an
understanding of the density of gases,fresh
air is given a density which = 1.

Prepared By | Safety Professional | www.safetygoodwe.com 37

DENSITY OF GASES AND VAPOURS

So gases, can then be compared with

air to see if they are lighter ( less dense )
or heavier ( more dense ).

Methane, the main component of natural

gas is lighter than air about half the
weight of air.

Prepared By | Safety Professional | www.safetygoodwe.com 38

DENSITY OF GASES AND VAPOURS

Ethane 1.05
Propane 1.55
Butane 2.00
Pentane 2.50
H2S 1.18
Carbon Monoxide 0.97
Methane 0.55

Prepared By | Safety Professional | www.safetygoodwe.com 39

 DENSITY OF GASES AND VAPOURS

Densities of Gas Clouds

The density of a flammable or toxic

gas cloud formed during a gas leakage
incident will depend not only on the
type of gas but more importantly on
its concentration within the gas cloud.

Prepared By | Safety Professional | www.safetygoodwe.com 40

 DENSITY OF GASES AND VAPOURS

Popular Myth Toxic H2S gas clouds are heavier

than air, usually not true!

(a) 1000 ppm H2S in pure natural gas is

lighter than air.

(b) 1000 ppm H2S in a gas cloud formed

from a high pressure release is neutral.

(c) 1000 ppm H2S entrapped in a condensate

vapour cloud is heavier than air.

Prepared By | Safety Professional | www.safetygoodwe.com 41

ATMOSPHERIC COMPOSITION

CARBON MONOXIDE
Same molecular weight as air (
same density as air)

HYDROGEN SULPHIDE
Heavier than air
(more dense)

METHANE
Lighter than air
(less dense)

Prepared By | Safety Professional | www.safetygoodwe.com 42

Prepared By | Safety Professional | www.safetygoodwe.com 43
Prepared By | Safety Professional | www.safetygoodwe.com 44
 CHARACTERISTICS OF GASES

·Remember the flammable and toxic limit

values for gases such as hydrogen sulphide
require relatively large mounts to produce a
flammable mixture where as the quantity
necessary to produce a toxic gas mixture is
extremely small.

Prepared By | Safety Professional | www.safetygoodwe.com 45

 APPLICATIONS AND TYPES OF PORTABLE GAS DETECTOR

Gas Test Detector Principle Measurement

Oxygen Electrochemical Cell % Volume

Methane or other
Catalytic or Infra-red % L.E.L.
Flammable gases
Infra-red or Tank scope % Volume

Electrochemical Cell
Toxic gases or Vapours or ppm
Chemical stain tube

Prepared By | Safety Professional | www.safetygoodwe.com 46

 ELECTROCHEMICAL SENSOR
Used in portable and fixed gas detectors to
detect and measure % oxygen and other toxic
gas concentrations of Hydrogen Sulphide
(H2S), Sulphur Dioxide, Carbon Monoxide,
Chlorine etc,

Prepared By | Safety Professional | www.safetygoodwe.com 47

 Catalytic Sensor

Platinum
Wire
• The catalytic sens
operate on the
combustion principl
they must be used
environments
containing oxygen
Catalytically-Treated
Metal oxide material
Prepared By | Safety Professional | www.safetygoodwe.com 48
THE CATALYTIC GAS SENSOR

Prepared By | Safety Professional | www.safetygoodwe.com 49

 THE CATALYTIC GAS SENSOR
A methane calibrated gas detector will detect many other flammable
gases and vapours, but may seriously under-read the concentration
present.

For example, on a methane calibrated catalytic gas detector:-

100% LEL propane or butane will only indicate about

50-60% LEL on the display

100% LEL pentane or hexane will only indicate about

35-45% LEL on the display
SUBSTANCE LEL (Vol%) UEL (Vol%)
ACETONE 2.15 13
ACETYLENE 2.4 88
BUTANE 1.5 8.5
ETHANE 3 15.5
ETHYLENE 2.7 34
HEXANE 1.2 7.4
HYDROGEN 4 75.6
METHANE 5 15
PROPANE 2 9.5
Prepared By | Safety Professional | www.safetygoodwe.com 50
 THE CATALYTIC GAS SENSOR

Limitations:
1. Cannot be used in an inert gas atmospheres – needs 13% or
more Oxygen.
2. Fails to danger due to Poisons and Blockage of flame
arrester
Silicones Water
De-greasing fluids Drilling fluids
Hot lube oils Oil

WD40
3. Methane calibrated detectors under-read concentrations of
higher hydrocarbon gases & vapours e.g. condensate vapours.
4. Older detectors can give ambiguous readings at high gas
concentrations
Prepared By | Safety Professional | www.safetygoodwe.com 51
THE CATALYTIC GAS SENSOR

Catalytic sensors are most

commonly calibrated to
methane for 0-100% LEL
full scale range

Why?
Prepared By | Safety Professional | www.safetygoodwe.com 52
 THE CATALYTIC GAS SENSOR

Methane gas is a very common gas

and is often encountered in many
applications

Prepared By | Safety Professional | www.safetygoodwe.com 53

HOW FREQUENT SHOULD YOU CALIBRATE YOUR
GAS DETECTOR?

• The only way to know that the readings are accurate is to expose t
instrument to known concentration test gas;
• To check the accuracy of the instrument on a regular basis

Prepared By | Safety Professional | www.safetygoodwe.com 54

 HOW FREQUENT SHOULD YOU CALIBRATE
YOUR GAS DETECTOR?

• Any instrument which may be used in a potentially hazardous locat

should be checked with a known concentration test gas before any
daily period of use.

• Normally 2.5% Methane in Air

Prepared By | Safety Professional | www.safetygoodwe.com 55

PREMIXED CALIBRATION GAS

Prepared By | Safety Professional | www.safetygoodwe.com 56

WHAT ARE THE BENEFITS FOR CALIBRATION?

Gas detectors are designed to help keep

your safe in potentially life threatening
environments.
If you test your instrument on a daily
basis you know that your readings are
accurate.
Confined spaces and other areas where
the air is potentially dangerous are
environments where you want to be sure
Prepared By | Safety Professional | www.safetygoodwe.com 57
Don’t take a chance
with your life.

Verify accuracy
daily!
Prepared By | Safety Professional | www.safetygoodwe.com 58
Summary

Prepared By | Safety Professional | www.safetygoodwe.com 59

 EXPLOSIVERANGE

100%
in volume

NO COMBUSTION (lack of oxygen)

UEL Upper Explosion Limit

HAZARDOUS AREA

LEL Lower Explosion Limit

Flammable gas
Sensor range No combustion (lack of gas

0%
in volume
Prepared By | Safety Professional | www.safetygoodwe.com 60
 PERMIT TO WORK

Prior to Hot-Work in zones 1 or 2 or a Enclosed Space, the areas

must be checked to make sure that it is safe for work to be carried
out.

This work is carried under the Permit to Work system,

part of this includes the signing by a competent person
that the atmosphere is safe to work in.

A. Hot Work in Zone 1 and 2 and near an enclosed

space

B. Enclosed Space Entry

C. Inerting Operations
Prepared By | Safety Professional | www.safetygoodwe.com 61
 GAS TEST DETAILS OF METER
1. Meter Serial numbers
2. Last Calibration date: (within one month of
today’s date.
3. Battery Check ( Condition)
4. Zero Check in fresh air
5. Check of hand or electrical operated pump
operation

Test for:
Oxygen, Flammable / Explosive and Toxic
vapours and gases
Prepared By | Safety Professional | www.safetygoodwe.com 62
Operating The Various Combustible Gas Detectors.

Some basic rules for operating gas detectors:

• Ensure you select a gas detector you know how to

operate.
• Check that it has been calibrated within the last
month.
• Look for any signs of damage or misuse.
• Turn it on and confirm the battery and
battery voltage are acceptable.
• Operate it in a safe and atmosphere area to ensure
it "zeros“ properly.

Prepared By | Safety Professional | www.safetygoodwe.com 63

Operating The Various Combustible Gas Detectors.

Refer to and perform the checks listed on the

instrument checklist.
• Know the limitations of each instrument
• Perform the procedures and retests, required by the
work permit or work plan.
• Go over the safety procedures and cover any special
safety "know how" with the men doing the work.
• Always allow at least 3 seconds for every metre of
hose for the sample to reach the sensor.
• Always approach and begin testing from upwind and in
the open fresh air.

Prepared By | Safety Professional | www.safetygoodwe.com 64

 Sampling Considerations:

• Oxygen level
• Type of combustibles
• Vapor density
• Temperature
• Wind and air movements
• Possible leak points and size
• Possible traps

REMEMBER .. Gas accumulations may be found

anywhere!
Prepared By | Safety Professional | www.safetygoodwe.com 65
Possible leakage points:

• FLANGES

• VALVE PACKING

• INSTUMENTS

• PUMP & COMPRESSOR SEALS

• TANK & MAHHOLES

• DECK DRAINS

Prepared By | Safety Professional | www.safetygoodwe.com 66

Gas testing only to be carried ou
by Authorised Gas Tester

Prepared By | Safety Professional | www.safetygoodwe.com 67

Sign Apparatus Out/ In in
LOG

Report Any Defects

Report Any Anomalies
Know Your Permit!

Prepared By | Safety Professional | www.safetygoodwe.com 68

 POTENTIAL HAZARDS

Prepared By | Safety Professional | www.safetygoodwe.com 69

 FIRE
The combination of fuel, air and
heat results in fire.

You may not SEE FLASH FIRE

You may not SMELL The combination of an
You may not TASTE accumulation of vapor with air
and heat in an open area will
But COMBUSTIBLES result in a flash fire.
can cause an unexpected
EXPLOSION
The combination of an
accumulation of vapor air and
heat in the right proportion in a
confined space results in
explosion.
Prepared By | Safety Professional | www.safetygoodwe.com 70
THANK YOU FOR YOUR ATTENTION

Prepared By | Safety Professional | www.safetygoodwe.com 71

 Conclusion.. Its just beginning

QUESTIONS

Prepared By | Safety Professional | www.safetygoodwe.com 72

Thank You

Prepared By | Safety Professional | www.safetygoodwe.com 73