Introduction to

HAZOP Study

Dr. AAProcess Control and Safety Group

2

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.

3

Points to ponder

What is the cause of the accident?

What is the consequence of the event?

What can we do to prevent all those things to happen?

What other possible accidents might happen on the road trip?

Can we be prepared before the accident occurs?

4

Can we make it more systematic?

Parameter Guideword Possible

Causes

Consequences Action Safeguard

Car speed Too fast

Too slow

Rushing Skidded when

emergency brake

- Slow down

- Speed up

-ABS brake

system

-Safety belt

- Air bag

Tire No thread

Less thread

Tire too old,

often speeding

and emergency

break

Car skidded - Check frequently

- Have spare tire

Window

visibility

Low

Very low

Rain Cannot see the

road

Car light Dim

No light

-Stop car

-Go to nearest

garage

-Use emergency

signal

Road With holes

Rocky

Breaks the car

tire

- Put a signboard

-Street lights

Travel time Night

Foggy

No street light -Travel during

daylight

Flash Drum Example

Consider the following Flash drum system. The purpose is to

separate multiple mixture of mostly A and B plus some other

heavy components to produce main product leaving the top at

90 mol % of A. Steam at 5 bar is used to bring the temperature

at the desired saturation temperature of 130 oC.

Nominal operating conditions are as follows:

T1= 70 oC

T2= 120 oC

T3= 100 oC

T4= 110 oC

P9 = 3 bar

6

FCV

7

FCV

2

FCV

5

TI

4

FI

1

TI

1

FI

6

FI

2

TI

3

TI

2

TI

8

FI

8

FI

9FCV

9

FCV

8

Process Fluid Steam

V-40E-30

E-20

XAD= 90 mol %

XAF=

50 mol %

Flash Drum Example

Problem 1 – Safety through automation

Consider the Flash Drum Plant. Propose

the required component of “safety

through automation” to provide safety

and operability.

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FCV

5

FCV

2

FCV

7

TI

4

TI

3

FI

1

TI

1

FI

6

FI

2

TI

3

TI

2

TI

8

FI

8

LIC

8

FI

9FCV

9

FCV

8

PIC

9

Process Fluid Steam

V-40

E-30

E-20

XAD= 90 mol %

XAF=

50 mol % TIC

7

Flash Drum Example

Is this good enough?

Problem 2 - HAZOP

Consider the Flash Drum as the HAZOP Study Node, conduct HAZOP

FCV

5

FCV

2

FCV

7

TI

4

TI

3

FI

1

TI

1

FI

6

FI

2

TI

3

TI

2

TI

8

FI

8

LIC

8

FI

9FCV

9

FCV

8

PIC

9

Process Fluid Steam

V-40

E-30

E-20

XAD= 90 mol %

XAF=

50 mol % TIC

7

Study node

10

HAZOP Terminology 1 – Node

A node is the 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

Flash Drum Example

– Separator as a node

– Other nodes: process to process heat exchanger, utility

heat exchanger

– Alternatively, each process line can be taken as a node.

Terminology 2 – Design Intent

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Description of how the process is expected to

behave at the Study Node.

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.

Flash Drum Example:

– To separate light components from the heavies (or to collect

light component at the top product stream)

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Terminology 3 - HAZOP Log Sheet

Deviation Causes Consequences Protection Action

Guideword +

Parameter

Guideword: No,

Less, More,

reverse etc

Parameter: Flow,

temperature,

level etc

Possible causes

of the deviation

Effect of deviation

of plant safety and

operability

Safety

provision

already

considered.

- Prevent

causes

- prevent/

reduce

consequence

- monitor/

detect

Is the protection

sufficient?

If not, propose

suitable action

or

recommendation

Based on the selected NODE and the design intent

of the node, HAZOP study is conducted. The

output is summarised in HAZOP Log Sheet

Example: Simplified HAZOP Log Sheet

Terminology 4 – Deviation

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Deviation is a way in which the process conditions

may depart from their INTENTION / DESIGN

INTENT

Expressed by combining parameters such as FLOW with

Guideword such as MORE to indicate MORE FLOW –

meaning the flow is more than the design intent.

Expresses as other unwanted condition such as

Contamination or corrosion.

Parameters: any process parameters such as Flow,

temperature, pressure, pH etc

Guideword: NO, MORE, LESS, AS WELL AS, PART

OF, OTHER THAN, REVERSE, etc.

The suggested guide words

– No: negation of design intention; no part of design

intention is achieved but nothing else happens

– More: Quantitative increase

– Less: Quantitative decrease

– As well as: Qualitative increase where all design intention

is achieved plus additional activity

– Part of: Qualitative decrease where only part of the

design intention is achieved

– Reverse: logical opposite of the intention

– Other than: complete substitution, where no part of the

original intention is achieved but something quite

different happens

When timing matters

Add the following guide words:– Early: something happens earlier in time than intended

– Late: something happens later in time than intended

– Before: something happens earlier in a sequence than intended

– After: something happens later in a sequence than intended

Terminology 5 – Causes

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The reason(s) why the DEVIATION could occur

More CAUSES can be identified for one

DEVIATION.

Flash Drum Example

– Causes for LESS LEVEL in V-40

• FCV8 stuck open

• LESS inlet Flow

• MORE Flow in line 8

• etcFCV

7

LIC

8

FCV

9

FCV8

PIC

9

Steam

V-40E-30

TIC

7

P8

Terminology 6 – Consequences

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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

Consequence for LESS LEVEL in V40

– V-40 empty, leading to pump P8 running dry

– No separation

FCV

7

LIC

8

FCV

9

FCV8

PIC

9

Steam

V-40E-30

TIC

7

P8

Terminology 7 – Protection

Sometimes termed as Safeguard, or Existing Provision

These are facilities that help to reduce the occurrence

frequency of the DEVIATION or to mitigate its

CONSEQUENCES.

There are, in principle, five types of SAFEGUARDS:

• Facilities that identify the DEVIATION. eg. alarm instrumentation and

human operator detection.

• Facilities that compensate the DEVIATION, e.g., an automatic control

system

• Facilities that prevent the DEVIATION to occur. e.g. 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 (SIS facility)

• Facilities that relieve the process from the hazardous DEVIATION.

These comprise for instance: pressure safety valves (PSV) and vent

systems. 18

Terminology 7- Protection

Flash Drum Example

– Protection against LESS LEVEL

in V40

• LIC8 controlling the liquid level

Is it enough???

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FCV

7

LIC

8

FCV

9

FCV8

PIC

9

Steam

V-40E-30

TIC

7

P8

Terminology 8 – Action/Recommendation

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.

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Terminology 8 – Action

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Existing Protection for LESS

LEVEL is considered not

adequate.

Actions Proposed

Add Low level Alarm (LAL

and LALL)

Add SIS to stop pump P8

when LALL triggered.

FCV

7

LIC

8

FCV

9

FCV8

PIC

9

Steam

V-40E-30

TIC

7

P8

Terminology 9 – Comments

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Various additional columns can be added to the

HAZOP Log Sheet.

Comments

– Any remarks to be given to the

ACTIONS/RECOMMENDATIONS or which, in another

way, showed up during the HAZOP sessions.

Action Party is also typically identified and noted

in the HAZOP Sheet.

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Flash Drum: Less Level

Deviation Causes Consequences Protection Action

Less Level

(Low Level)

Valve FCV8 stuck

open

Less feed

LIC8 malfunction

• Level drop

leading to dry

separator, hence

no separation

• Risk of pump

running dry

(damage)

LIC8 •Install LAL

•Install LALL

with SIS to stop

pump P8

Note:

• Sometimes, more than one consequences may arise and for each

consequence, different actions are required

•Sometimes different causes require different actions

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FCV

7

FCV

2

FCV

5

TI

4

TI

3

FI

1

TI

1

FI

6

FI

2

TI

3

TI

2

TI

8

FI

8

LIC

8

FI

9FCV

9

FCV

8

PIC

9

Process Fluid Steam

V-40

E-30

E-20

XAD= 90 mol %

XAF=

50 mol % TIC

7

Flash Drum Example

Now, consider MORE PRESSURE as deviation

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Flash Drum: MORE PRESSURE

Deviation Causes Consequences Protection Action

More Pressure

(High Pressure)

Valve FCV9 stuck

Close

PIC Malfunction

• increase in

pressure leading to

risk of explosion

PIC8 •Install PAH

•Install Pressure

relieve valve

More

temperature in

Feed

TIC7

HAZOP STUDY TEAM

HAZOP Team

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HAZOP

Leader

HAZOP

SecretaryCORE Team

Project Process Engineer

Independent Process

Engineer

Project Instrument

Engineer

Operation Representative

(covering maintenance)

Specialists

(as required)

Maintenance Engineer

Corrosion Engineer

Pipeline Engineer

Others

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

responsibility for the process and/or the performance of operations)

Responsibility of HAZOP Team Members

Plan sessions and timetable

– Agree on the nodes, study approach etc

– Be thorough

Manage the HAZOP Team

– Control and limit discussion when necessary

– Encourage team to actively participate, be creative, draw conclusion

– Keep team in focus. If conflict arises, handle with care.

– Do not let anybody (including the leader himself to dominate).

– Judge importance issues

Stop the team trying to redesign the process.

Leader must be strong, yet diplomatic.

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Responsibility of Team Members

HAZOP Secretary

– Take adequate notes and record documentations

– Inform leader if more time required in taking notes

– Produce draft report of study

Team Members

– Provide inputs based on the discipline that they

represent e.g., instrumentation, process, operation etc.

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Questioning Techniques

Open questions

– Help person being asked to think – use words how, what and why.

Closed questions

– To focus on an issue or problem. Start with words who, when, where.

– Required answer yes or no only.

Question mix

– Mix between open and closed questions.

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Things to avoid

– Ambiguous or vague questions.

– Double barelled/multiple questions.

– Long complicated questions.

– Interrogation type of questions.

– A loaded questions – implied judgement.

Questioning Techniques

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Required information

P & IDs

Process flow diagrams

Heat and Material Balances

Layouts

Logic Diagrams

Equipment Data Sheets

Material Hazard Data Sheets

Hazardous area Layouts

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Modes of operation to consider

The following modes of plant operation should be

considered for each node:

– Normal operation

– Reduced throughput operation

– Routine start-up

– Routine shut-down

– Emergency shutdown

– Commissioning

– Special operating modes

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HAZOP meeting

Proposed agenda:

• Introduction & presentation of participation

• Overall presentation of the system/operation to be analyzed

• Description of the HAZOP approach

• Presentation of the first node or logical part of the operation

• Analyze the first node/ part using the guide-words and parameters

• Continue presentation and analysis (steps 4 & 5)

• Coarse summary of findings

Focus should be on potential hazards as well as potential operational problems.

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Does any other guideword combine with this parameter to give a meaningful deviation?

Specify the section or stage to be examined

Describe & discuss the step/ operation; determine the design envelope.

Develop & record the design intention

From the description and the design intention select a parameter

Combine this parameter with a guideword to develop a meaningful deviation

Seek a possible cause of the deviation and identify the consequences

Evaluate the safeguards and decide if they are adequate of if a change

or further study is needed.

Have all causes of this deviation been considered?

YES

Are there further parameters to consider?

Examination of the steps/ stage is complete

NO

NO

YES

YES

NO

PHASE 2: SELECT A LINE

Record

Divide section into Study nodePHASE 1: DIVIDE SECTION

PHASE 3:

ANALYSIS

PHASE 4: RECORDING

PHASE 5: REEVALUATE

Sequence for conducting a HAZOP Study

Flow diagram for the HAZOP analysis – The parameter-first approach

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How to be a good HAZOP participant

Be active! Everyone contribution is important

Be to the point. Avoid endless discussion of details

Be critical in a positive way – not negative, but constructive

Be responsible. He who knows should let the other know

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HAZOP recording

The findings are recorded during the meeting(s) using a HAZOP work-sheet, either by filling in paper copies, or by using a computer connected to a projector (recommended).

The HAZOP worksheet may be different depending on the scope of the study – generally the following entries (columns) are included• Ref. no.

• Guidewords

• Deviations

• Possible causes

• Consequences

• Safeguards

• Actions required (or, recommendations)

• Actions allocated to (follow up responsibility)

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Process HAZOP worksheet

Hazards and Operability Review

Project Name: Date: Page of

Process :

Section: Ref.

Drawing:

Item Study

node

Process

Parameter

Deviations

(guide words)

Possible

causes

Possible

consequences

Action

Required

HAZOP Worksheet

Plant Secretary:

Drawings referred to Team Names:

Equipment Properties: Flow Pressure Temperature

Equipment Tag Numbers Guide Words: No More Less Opposite Also

Other (Early Late)

Special conditions for Hazop:

none, start-up, abnormal operation, maintenance, other (details):

Line

no.

Deviation Cause Consequences Safeguard Action

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40

FCV

5

FCV

2

FCV

7

TI

4

TI

3

FI

1

TI

1

FI

6

FI

2

TI

3

TI

2

TI

8

FI

8

LIC

8

FI

9FCV

9

FCV

8

PIC

9

Process Fluid Steam

V-40

E-30

E-20

XAD= 90 mol %

XAF=

50 mol % TIC

7

Flash Drum Example

Now, complete the HAZOP Study

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Some References

Frank P. Lees (1980). “Loss Prevention in the Process Industries.

Hazard Identification, Assessment and Control.” Volume 1. Butterworth

& Co (Publishers) Ltd.

Frank P. Lees (1980). “Loss Prevention in the Process Industries.

Hazard Identification, Assessment and Control.” Volume 2. Butterworth

& Co (Publishers) Ltd.

Frank Crawley, Malcolm Preston & Brian Tyler (2000). “HAZOP: Guide to

best practice. Guidelines to best practice for the process and chemical

industries”. Institution of Chemical Engineers, UK.

Risk Management Group (1992). “Hazard & Operability Studies. Basic

2-day Training Course Notes.” ICI Australia Engineering Pty Ltd.

Marvin Rausand (2004). “HAZOP. Hazard and Operability Study.”

Department of Production and Quality Engineering, Norwegian

University of Science and Technology.