hsb46a

8/13/2019 hsb46a

1/3

HEALTH AND SAFETY BRIEFING

No 46a

January 2007

Hazard and Operability Studies (HAZOP)

Introduction

Other Health and Safety Briefings have discussed aspects of Risk Assessment:

Risk Assessment Practical Application in the Workplace Risk Assessment Legal Position and Interpretation Quantified Risk Assessment Techniques (Part 1) Failure Modes and Effects

Analysis (FMEA)

Quantified Risk Assessment Techniques (Part 2) Event Tree Analysis (ETA) Quantified Risk Assessment Techniques (Part 3) Fault Tree Analysis (FTA) Hazard Analysis - (HAZAN)

This Briefing Note is intended to explain the meaning of the term Hazard and Operability

Studies (HAZOP). It is intended merely to illustrate the technique and its vocabulary and

is in no sense intended to be a definitive treatment.

HAZOP

Hazop is structured technique, which may be applied typically to a chemical production

process, identifying hazards resulting from potential malfunctions in the process. It is

essentially a qualitative process. A HAZOP study would typically be undertaken by amulti-disciplinary team involving chemists, engineers, production managers, designers

and safety specialists etc. asking a series of what if? questions. By undertaking a

HAZOP study at an early design stage, potential problems can be avoided instead of

having to make costly modifications after the plant is built. The HAZOP team would

systematically examine a proposed process design by asking questions using guidewords

representing deviations from the intended parameters of the process i.e:

Guide Words Meaning

No or None The negation of the intention (e.g. no flow)

More A quantitative increase (e.g. high pressure)

Less A quantitative decrease (e.g. low pressure)

As well as In addition to (e.g. impurity)

Part of A qualitative decrease (e.g. only one of two components present)

Reverse The opposite of the intention (e.g. backflow)

Other than Complete substitution (e.g. wrong material)

Table 1

2007 The IETThe Institution of Engineering and Technology is a not-for-profit organisation,registered as a charity in the UK

8/13/2019 hsb46a

2/3

Table 2 indicates the type of problems that could be associated with different types of

deviation:

Type of Deviation Typical Problems

No flow Blockage, pump failure, valve closed or jammed, suction vessel

empty, vapour lock, control failure etc.

Reverse flow Pump failure, non-return valve failure, pump reversed, over

pressurisation etc.

More temp.

More pressure

Blockage, loss of control, reaction, explosion, valve closed, high

ambient temperature etc.

Less flow Pump failure, leak, partial blockage, sediment, cavitation, poor

suction head etc.

Less temp.

Less pressure

Heat loss, vapourisation, leak, inbalance of input and output etc.

As well as Presence of contaminants, e.g. water, air, lubrication oil,

corrosion products, presence of other process products due to

leakage etc.

Table 2

An example to illustrate the process could be the delivery of liquid propane to a fixed tank

currently fitted with a pressure relief valve and a liquid level gauge. Table 3 indicates

how HAZOP could be applied to this simple situation.

Deviation Cause of deviation Consequences Existing

controls

Possible action

More level 1. Overfilling Humanerror

2. Pump fails ON

Release through relief

valve

As above

Level gauge

As above

Consider high level alarm

As above

Less level 1. Leak

2. Not filled properly Human error

Release to atmosphere

Economic losses

None

Level gauge

Review

inspection/maintenance

regime and consider gas

detectors

More

temperature

Fire near vessel Possible release and

escalation

None Consider automatic sprinkler

and fire procedures

More pressure Relief valve fails closed Vessel

overpressure/rupture

None Consider high pressure

alarm

Less pressure 1.

Relief valve fails open Release to atmosphere None Consider detection andemergency planning


8/13/2019 hsb46a

3/3

2. Filling hose ruptures As above Operator action Check integrity of hose andquality control

As well as 1. Water contamination2. Impurities

Out of spec. supply

As above

None

None

Review QA procedures

As above and can reaction

occur

Other than Wrong substance delivered Possible reaction None Review QA procedures/can

reaction occur

Table 3

Under Possible Action will be listed possible mitigating measures as well as questions

needing resolution. This example is given merely to illustrate the principle underlying the

technique. The actual use of the technique requires knowledge derived from a team of

different specialists with an experienced group leader.

Further reading:

Chemical Industries Health and Safety Council (1977) Hazard and OperabilityStudies. Chemical Industries Association: London

Lees F P (1981) Some features of and activities in HAZOP studies. The ChemicalEngineer

Kletz T A (1986) HAZOP & HAZAN Notes on the Identification and Assessmentof Hazards The Institution of Chemical Engineers: London

These Briefings contain a summary of recent Health & Safety issues, provided for general

information purposes only, and should not be relied upon as legal advice. The IET has

tried to make the Briefings accurate and informative, but they have not been prepared by

a lawyer and may not constitute an up-to-date summary of the law. The IET accepts no

liability for your use of these Briefings. Further details and information on broader

Health & Safety issues can be obtained from the Governments Health and Safety

Executive. Legal advice should be obtained on any specific issues.

The IET is unable to provide further information on this topic. Please contact the

HSE.

For information about the IET's Health and Safety Policy Advisory Groupplease contact:

Health and Safety Policy Advisory Group Secretary

Policy Department

IET

Six Hills Way

Stevenage

Herts

SG1 2AY

http://www.hse.gov.uk/http://www.theiet.org/publicaffairs/panels/health/index.cfmhttp://www.theiet.org/publicaffairs/panels/health/index.cfmhttp://www.hse.gov.uk/

hsb46a

Documents