Hazard and

Operability
Study
(HAZOP)
 I suppose that I
should have done that
HAZOP Study!
A scenario…

You and your family are on a road trip by using a car

in the middle of the night. You were replying a text
message while driving at 100 km/h and it was raining
heavily. The car hits a deep hole and one of your tire
blows.

You hit the brake, but due to slippery road and your
car tire thread was thin, the car skidded and was
thrown off the road.
Points to ponder

What was the cause of the accident?

What was the consequence of the event?

What can we do to prevent all those things to happen in the first

place?

What other possible accidents might happen on the road trip?

Can we be prepared before the accident occurs?

 Can we make it more systematic?

Parameter Guideword Possible Consequences Action Safeguard

Causes
Car speed Too fast Rushing Skidded when - Slow down -ABS brake
Too slow emergency brake - Speed up system
-Safety belt
- Air bag
Tire No thread Tire too old, Car skidded - Check frequently
Less thread often speeding - Have spare tire
and emergency
break
Window Low Rain Cannot see the
visibility Very low road

Car light Dim -Stop car

No light -Go to nearest
garage
-Use emergency
signal
Road With holes Breaks the car - Put a signboard
Rocky tire -Street lights
Travel time Night No street light -Travel during
Foggy daylight
What is a HAZOP study?

▪ Systematic technique to IDENTIFY potential HAZard

and OPerating problems
▪ Involves a multi-disciplinary team methodically
“brainstorming” the plant design
▪ A qualitative technique based on “guide-words” to
help provoke thoughts about the way deviations from
the intended operating conditions can lead to
hazardous situations or operability problems
 What is a HAZOP study?
▪ A HAZOP study is an examination procedure.
▪ Its purpose is to identify all possible deviation from the way
in which a design is expected to work and to identify all the
hazards associated with these deviations.
▪ When deviation arise that results in hazards, action are
generated that require design engineers to review and
suggest solutions to remove the hazard or to reduce its risk
to an acceptable level.
Origin of HAZOP study
▪ HAZOP were initially 'invented' by ICI in the United Kingdom, but
the technique only started to be more widely used within the
chemical process industry after the Flixborough disaster in 1974.
▪ This chemical plant explosion killed twenty eight people and
injured scores of others, many of those being members of the
public living nearby.
▪ Through the general exchange of ideas and personnel, the system
was then adopted by the petroleum industry, which has a similar
potential for major disasters.
▪ This was then followed by the food and water industries, where
the hazard potential is as great, but of a different nature, the
concerns being more to do with contamination rather than
explosions or chemical releases.
Potential Hazard AND Operability
Problems

Why the big AND ?

Potential Hazard AND Operability Problems

Because of the high profile of production plant

accidents, emphasis is too often placed upon the
identification of hazards to the neglect of potential
operability problems.

Yet it is in the latter area that benefits of a HAZOP

Study are usually the greatest.
 Example
▪ A study was commissioned for a new plant.
▪ Some two years previously, and for the first time, a similar
study had been carried out on different plant at the same
site which was then in the process of being designed.
▪ Before the latest review commenced, the Production
Manager expressed the hope that the same benefits would
accrue as before, stating that

“In his twenty years of experience, never had a new plant

been commissioned with so few problems, and no other
plant had ever achieved its production targets and break-
even position in so short a time".
Objectives of a HAZOP study
Safety Issues:
– To identify scenarios that would lead to the release of hazardous
or flammable material into the atmosphere, thus exposing
workers to injury
– To check the safety of the design
– To improve the safety of an existing and or modified facility

Operability Issues:
– To decide whether and where to build
– To check operating and safety procedures
– To verify that safety instrumentation is working optimally
– To facilitate smooth, safe prompt start-up
– To minimize extensive last minute modifications
– To ensure trouble-free long-term operation

“Prevention is better than control”

Philosophy – Hazard vs Operability

▪ HAZOPs concentrate on identifying both hazards as

well as operability problems. While the HAZOP study
is designed to identify hazards through a systematic
approach, more than 80% of study recommendations
are operability problems and are not, of themselves,
hazards.
▪ Although hazard identification is the main focus,
operability problems should be identified to the
extent that they have the potential to lead to process
hazards, result in an environmental violation or have
a negative impact on profitability.
Definition of Hazard & Operability

▪ Hazard - any operation that could possibly cause a

catastrophic release of toxic, flammable or explosive
chemicals or any action that could result in injury to
personnel.
▪ Operability - any operation inside the design
envelope that would cause a shutdown that could
possibly lead to a violation of environmental, health or
safety regulations or negatively impact profitability.
Benefits

▪ The circumstances when HAZOPs are

likely to produce benefits are:
– during the design or installation of any new
plant or process, or major modification to an
existing one;
– when there are unique hazards such as
environmental hazards and quality or cost
issues associated with the operation;
– following a major incident involving fire,
explosion, toxic release etc; and
– to justify why a particular code of practice,
guidance note or industry code is not to be
followed.
When should a HAZOP be held

▪ During various stages of plant design

– At the beginning of the project as a ‘safety and environmental specification’
– Towards the end of process definition, when the Process Flow sheets are
available as a Safety and Environmental Review
– When P&IDs are at ‘Approved for Design’ stage (Final design HAZOP)
▪

 During construction site inspections ensure that

▪ recommendations arising from the HAZOP or other
safety and environmental reviews are being
▪ implemented.
 A pre-commissioning study reviews plant
procedures and perform a conventional safety
audit
 Once operational, an audit of plant and
procedures at regular interval ensures
ongoing safety awareness
 HAZOP study of existing plant

▪ Can be done at any time

▪ Mainly used to improve operating procedures or when
modifying plant
▪ Sometimes used to identify possible improvements in plants
where accident or incident rate is abnormally high
▪ Can be used in conjunction with plant safety audits
▪ Needs exceptional care to fully define the scope and aims of
the study
▪ Despite detailed operation knowledge, much of the original
design intent is often unknown
Simple Example of a HAZOP Study

Diammonium Phosphate (DAP) Production

▪Phosphoric acid and ammonia are mixed, and a non-

hazardous product, diammonium phosphate (DAP), results if
the reaction of ammonia is complete. If too little phosphoric
acid is added, the reaction is incomplete, and ammonia is
produced. Too little ammonia available to the reactor results in
a safe but undesirable product.
▪Both chemicals will be used in large quantities and in
concentrated form. Due to the highly corrosive nature
of both chemicals, the project team was assigned to
investigate the hazards posed to staff from the reaction
resulting from study line 1 (phosphoric acid delivery
line).
Production of DAP (continuous process)

Valve A

Phosphoric Acid

Study line 1
Phosphoric acid delivery line

Valve C
Valve B

Ammonia
Diammonium
Phosphate
(DAP)

Reactor
HAZOP Study Report on line 1 of DAP
Preliminary HAZOP Example

Monomer Cooling Coils Refer to reactor system shown.

Feed
The reaction is exothermic. A cooling
system is provided to remove the excess
energy of reaction. In the event of cooling
Cooling Water function is lost, the temperature of reactor
to Sewer would increase. This would lead to an
increase in reaction rate leading to
additional energy release.

Cooling The result could be a runaway reaction

Water In with pressures exceeding the bursting
pressure of the reactor. The temperature
within the reactor is measured and is
used to control the cooling water flow rate
by a valve.
TC
Thermocouple Perform HAZOP Study
Preliminary HAZOP on Reactor - Example

Guide Word Deviation Causes Consequences Action

NO No cooling Temperature
increase in reactor

REVERSE Reverse Failure of water

cooling flow source resulting
in backward flow
MORE More cooling Instruct
flow operators on
procedures
AS WELL AS Reactor Check
product in maintenance
coils procedures and
schedules
OTHER THAN Another Water source
material contaminated
besides
cooling water
Preliminary HAZOP on Reactor – Answer
Guide Word Deviation Causes Consequences Action
NO No cooling Cooling water valve Temperature increase Install high
malfunction in reactor temperature alarm
(TAH)
REVERSE Reverse Failure of water Less cooling, Install check valve
cooling flow source resulting in possible runaway
backward flow reaction

MORE More cooling Control valve Too much cooling, Instruct operators
flow failure, operator reactor cool on procedures
fails to take action
on alarm

AS WELL AS Reactor More pressure in Off-spec product Check

product in coils reactor maintenance
procedures and
schedules

OTHER THAN Another Water source May be cooling If less cooling,

material contaminated inefffective and effect TAH will detect. If
besides on the reaction detected, isolate
cooling water water source.
Back up water
source?
 HAZOP – The Critical Success Factor

▪ The HAZOP process is based on the principle that a

team approach to hazard analysis will identify more
problems than when individuals working separately
combine results. The HAZOP
▪ team is made up of individuals with varying
backgrounds and expertise.
▪ The expertise is brought together during HAZOP
sessions and through a collective brainstorming effort
that stimulates creativity and new ideas, a thorough
review of the process under consideration is made.
HAZOP Terminology - 1
Term Definition

Cause The reason(s) why the DEVIATION could occur. More

CAUSES can be identified for one DEVIATION.

Comments Any remarks to be given to the RECOMMENDATIONS or

which, in another way, showed up during the HAZOP
sessions.

Consequence The results of the DEVIATION, in case it occurs.

CONSEQUENCES may both comprise process hazards
and operability problems, like plant shutdown. More
CONSEQUENCES can follow from one cause and, in turn,
one CONSEQUENCE can have several CAUSES.
HAZOP Terminology - 2
Term Definition
Deviation A way in which the process conditions may depart from their
INTENTION.
Intention / Design Description of how the process is expected to behave at the
intent Study Line. This is qualitatively described as an activity (e.g.,
feed, reaction, sedimentation) and/or quantitatively in the
process parameters, like temperature, flow rate, pressure,
composition, etc.

Keyword/ A short word to create the imagination of a DEVIATION of the

Guideword INTENTION. The mostly used set of Guidewords is: NO, MORE,
LESS, AS WELL AS, PART OF, OTHER THAN and REVERSE. The
GUIDEWORDS are applied, in turn, to all the PARAMETERS, in
order to identify unexpected and yet credible DEVIATIONS from
the INTENTION.
 HAZOP Terminology - 3
Term Definition

Parameter The relevant parameter for the condition(s) of the process,

e.g., pressure, temperature, composition, etc.
Study Line/ Node A specific location in the process in which (the deviations
of) the process intention are evaluated. Examples might
be: separators, heat exchangers, scrubbers, pumps,
compressors, and interconnecting pipes with equipment
Recommendation Activities identified during a HAZOP study for follow-up.
These may comprise technical improvements in the
design, modifications in the status of drawings and
process descriptions, procedural measures to be
developed or further in-depth studies to be carried out.
HAZOP Terminology - 4
Term Definition
Facilities that help to reduce the occurrence frequency of
Safeguard the DEVIATION or to mitigate its CONSEQUENCES. There
are, in principle, five types of SAFEGUARDS:
❑ Facilities that identify the DEVIATION. These comprise, among
others, alarm instrumentation and human operator detection.
❑ Facilities that compensate the DEVIATION, e.g., an automatic
control system that reduces the feed to a vessel in case of
overfilling it (increase of level). These usually are an integrated part
of the process control.
❑ Facilities that prevent the DEVIATION to occur. An example is an
inert blanket gas in storages of flammable substances.
❑ Facilities that prevent a further escalation of the DEVIATION,
e.g., by (total) trip of the activity. These facilities are often
interlocked with several units in the process, often controlled by
logical computers.
❑ Facilities that relieve the process from the hazardous
DEVIATION. These comprise for instance: pressure safety valves
(PSV) and vent systems.
 HAZOP Terminology - 4
Term Definition
Action –Where a credible cause results in a negative consequence, it
must be decided whether some action should be taken. It is at
this stage that consequences and associated safeguards are
considered. If it is deemed that the protective measures are
adequate, then no action need be taken, and words to that effect
are recorded in the Action column.
– Actions fall into two groups:
• Actions that remove the cause.
• Actions that mitigate or eliminate the consequences.
– Whereas the former is to be preferred, it is not always
possible, especially when dealing with equipment malfunction.
However, always investigate removing the cause first, and only
where necessary mitigate the consequences.
HAZOP Methodology - Content

▪ HAZOP Study Planning and Preparations

▪ HAZOP Study Team - Role and Responsibilities
▪ Meeting Arrangements
▪ Reporting and Follow-up
▪ HAZOP Guidewords;
▪ Possible Causes & Consequences
▪ Plant; Safeguards & Action Required
▪ Working Session 2: Chemical Plant
HAZOP Planning and Execution
CLOSE OUT
Record/File
Completed
Actions
TRACK
ACTIONS
HAZOP
Review
Meeting
REPORT
Action List
HAZOP
Report
TEAM
System
Assessment
Team Activity
PLAN
Select Team
Examine System
Keywords
HAZOP study team
▪ Independent leader (e.g., not from plant studied)
– Preferred but complete independence not essential
▪ Project engineer
– Provide engineering input
▪ Operations representative
– Plant operation
▪ Discipline engineers
– Process
– Instrument/ electrical
– Mechanical/ maintenance
▪ HAZOP minute recorder
– One of the above
Responsibility of HAZOP Team Members

HAZOP leader - The leader should be independent (i.e. has no

responsibility for the process and/or the performance of operations)
•Plan sessions and timetable
•Control discussion
•Limit discussion
•Encourage team to draw conclusion
•Ensure secretary has time for taking note
•Keep team in focus
•Encourage imagination of team members
•Motivate members
•Discourage recriminations
•Judge importance issues
Checklist for HAZOP Leader
▪ Always prepare study program in advance.
▪ Agree on the format or form to be used.
▪ Prepare follow up procedures.
▪ Brief members about HAZOP during first meeting.
▪ Stop the team trying to redesign the process.
▪ HAZOP is a team exercise. Do not let anybody (including
the leader himself to dominate).
Checklist for HAZOP Leader
▪ If conflict arises, handle with care.
▪ Avoid long discussions by recording areas which need to be
resolved outside meeting.
▪ Leader must be strong, yet diplomatic.
▪ Speak clearly. Make you point.
▪ Better have experience working as team member previously.
▪ Do not skip anything….some time small things may cause big
accident.
Responsibility of HAZOP Team Members

HAZOP Secretary

• Take adequate notes

• Record documentations
• Inform leader if more time required in taking notes
• If unclear, check wording before writing
• Produce interim lists of recommendations
• Produce draft report of study
• Check progress of chase action
• Produce final report
Responsibility of HAZOP Team Members

Process Engineer

• Provide a simple description

• Provide design intention for each process unit
• Provide information on process conditions and design conditions
• Provide a simple description
• Provide design intention for each process unit
• Provide information on process conditions and design conditions
Responsibility of HAZOP Team Members

Mechanical Design Engineer

• Provide specification details

• Provide vendor package details
• Provide equipment and piping layout information

Instrument Engineer

• Provide details of control philosophy

• Provide interlock and alarm details
• Provide info on shutdown, safety features
 Responsibility of HAZOP Team Members

Plant Engineer or Manager

• Provide information on compatibility with any existing adjacent plant
• Provide details of site utilities and services
• Provide (for study on existing plant) any update on maintenance access and
modifications
Shift Operating Engineer or Supervisor
• Provide guidance on control instrumentation integrity from an operating
experience view point
• Provide (for study on existing plant) information on plant stability at the
specified control parameters
• Provide information on experienced operability deviations of hazard
potential
Responsibility of HAZOP Team Members

Chemist

• Provide details of process chemistry

• Provide details of process hazards (polymerisations, byproducts,
corrosion etc)

Project Engineer

• Provide details of cost and time estimation and also budget constraints.
• Ensure rapid approval if required
HAZOP Exercise
Case Study – Shell & Tube Heat Exchanger

▪ Using relevant guide works, perform HAZOP study on shell & tube heat exchanger

Process
fluid

Cooling water
 HAZOP on Heat Exchanger – Answer 1

Guide Word Deviation Causes Consequences Action

Less Less flow of Pipe blockage Temperature of High
cooling process fluid Temperature
water remains constant Alarm
More More cooling Failure of Temperature of Low
flow cooling water process fluid Temperature
valve decrease Alarm
More of More Failure of Bursting of tube Install high
pressure on process fluid pressure alarm
tube side valve
Contamination Contaminati Leakage of Contamination of Proper
on of tube and process fluid maintainance
process fluid cooling water and operator
line goes in alert
Corrosion Corrosion of Hardness of Less cooling and Proper
tube cooling water crack of tube maintainence
 HAZOP on Heat Exchanger – Answer 2

Guide Word Deviation Causes Consequences Action

NONE No cooling Failure of inlet Process fluid Install
water flow cooling water temperature is not Temperature
valve to open lowered indicator before
and after the
accordingly process fluid line
Install TAH

MORE More cooling Failure of inlet Output of Process Install

water flow cooling water fluid temperature Temperature
valve to close too low indicator before
and after process
fluid line
Install TAL

LESS Less cooling Pipe leakage Process fluid Installation of flow

water temperature too low meter

REVERSE Reverse Failure of process Product off set Install check valve
process fluid fluid inlet valve (whether it is
flow crucial have to
check?)

CONTAMINATIO Process fluid Contamination in Outlet temperature Proper

N contamination cooling water too low maintenance and
operator alert