Learning Unit 4 HAZOP STUDY NOTES
4.1 Background
HAZard and OPrability Analysis (HAZOP) is a structured systematic technique for system examination
and risk management. It is often used as technique for identifying potential hazards in a system and
identifying operability problems likely to lead to non-conforming products. HAZOP is based on a
theory that assumes risk events are caused by deviations from design or operating intentions.
Identification of such deviations is facilitated by using set of “GUIDE WORDS” as a systematic list of
deviation perspectives. These guide words help stimulate the imagination of team members when
they explore potential deviations.
As a risk assessment tool, HAZOP is often described as:
- A brainstorming technique
- A qualitative risk assessment tool
- An inductive risk assessment tool.
4.2 HAZOP Objectives
(a) Identify all deviations from the way a system is intended to function: their causes, and all the
hazards and operability problems associated with these deviations.
(b) Decide whether actions are required to control the hazards and/or the operability problems,
and if so, identify the ways in which the problems can be solved.
(c) Identify cases where a decision cannot be made immediately, and decide on what
information or actions are required.
(d) Ensure that actions decided are followed up.
(e) Make operator aware of hazards and operability problems.
4.3 When to perform HAZOP?
The HAZOP study should preferably be carried out as early in the design phase as possible – to have
influence on the design. On the other hand; to carry out a HAZOP we need a rather complete design.
As a compromise, the HAZOP is usually carried out as a final check when the detailed design has
been completed. A HAZOP study may also be conducted on an existing facility to identify
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, modifications that should be implemented to reduce risk and operability problems. HAZOP studies
may also be used more extensively, including:
- At the initial concept stage when design drawings are available
- When the final piping and instrumentation diagrams (P&ID) are available
- During construction and installation to ensure that recommendations are implemented
- During commissioning
- During operation to ensure that plant emergency and operating procedures are regularly
reviewed and updated as required
4.4 Some of important guide words used
Some of popular guidewords used are shown in Figure 1, below
Figure 1: Guide words
A deviation from intention is formulated by combining the guide word with process parameter.
Examples of process parameters are Flow, Composition, pH, Pressure, Addition Sequence,
Temperature, Separation, Signal, Mixing, Time, Start/stop, Stirring, Phase, Operate, Transfer, Speed,
Maintain, Level, Particle size, Services, Viscosity Measure, Communication, Reaction, Control etc
For example
NO FLOW
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4.1 Background
HAZard and OPrability Analysis (HAZOP) is a structured systematic technique for system examination
and risk management. It is often used as technique for identifying potential hazards in a system and
identifying operability problems likely to lead to non-conforming products. HAZOP is based on a
theory that assumes risk events are caused by deviations from design or operating intentions.
Identification of such deviations is facilitated by using set of “GUIDE WORDS” as a systematic list of
deviation perspectives. These guide words help stimulate the imagination of team members when
they explore potential deviations.
As a risk assessment tool, HAZOP is often described as:
- A brainstorming technique
- A qualitative risk assessment tool
- An inductive risk assessment tool.
4.2 HAZOP Objectives
(a) Identify all deviations from the way a system is intended to function: their causes, and all the
hazards and operability problems associated with these deviations.
(b) Decide whether actions are required to control the hazards and/or the operability problems,
and if so, identify the ways in which the problems can be solved.
(c) Identify cases where a decision cannot be made immediately, and decide on what
information or actions are required.
(d) Ensure that actions decided are followed up.
(e) Make operator aware of hazards and operability problems.
4.3 When to perform HAZOP?
The HAZOP study should preferably be carried out as early in the design phase as possible – to have
influence on the design. On the other hand; to carry out a HAZOP we need a rather complete design.
As a compromise, the HAZOP is usually carried out as a final check when the detailed design has
been completed. A HAZOP study may also be conducted on an existing facility to identify
1|Page
, modifications that should be implemented to reduce risk and operability problems. HAZOP studies
may also be used more extensively, including:
- At the initial concept stage when design drawings are available
- When the final piping and instrumentation diagrams (P&ID) are available
- During construction and installation to ensure that recommendations are implemented
- During commissioning
- During operation to ensure that plant emergency and operating procedures are regularly
reviewed and updated as required
4.4 Some of important guide words used
Some of popular guidewords used are shown in Figure 1, below
Figure 1: Guide words
A deviation from intention is formulated by combining the guide word with process parameter.
Examples of process parameters are Flow, Composition, pH, Pressure, Addition Sequence,
Temperature, Separation, Signal, Mixing, Time, Start/stop, Stirring, Phase, Operate, Transfer, Speed,
Maintain, Level, Particle size, Services, Viscosity Measure, Communication, Reaction, Control etc
For example
NO FLOW
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