HAZOP uses a brainstorming approach around a series of guide words designed to qualitatively identify possible deviations from normal operation and their possible impacts. Responsibilities are assigned to investigate possible solutions for each problem found.
Guidance is given on study procedure and prerequisites for an effective HAZOP, including team selection, information requirements and record keeping.
To be effective, a HAZOP study must be systematic, detailed and conducted by a balanced team with an experienced leadership.
Effective HAZOP strategy:
The effectiveness of a HAZOP will depend on:
- the accuracy of information (including P&IDs) available to the team — information should be complete and up-to-date
- the skills and insights of the team members
- how well the team is able to use the systematic method as an aid to identifying deviations
- the maintaining of a sense of proportion in assessing the seriousness of a hazard and the expenditure of resources in reducing its likelihood
- the competence of the chairperson in ensuring the study team rigorously follows sound procedures.
Key elements of a HAZOP are:
- HAZOP team
- full description of process
- relevant guide words
- conditions conducive to brainstorming
- recording of meeting
- follow up plan
The HAZOP work-sheets may be different depending on the scope of the study.
Generally the following entries (columns) are included:
- Ref. no.
- Possible causes
- Actions required (or, recommendations)
- Actions allocated to (follow-up responsibility)
As a basis for the HAZOP study the following information should be available:
- Process flow diagrams
- Piping and instrumentation diagrams (P&IDs)
- Layout diagrams
- Material safety data sheets
- Provisional operating instructions
- Heat and material balances
- Equipment data sheets Start-up and emergency shut-down procedures
Though there are no fixed approaches, following is a typical HAZOP procedure:
- Divide the system into sections (i.e., reactor, storage)
- Choose a study node (i.e., line, vessel, pump, operating instruction)
- Describe the design intent
- Select a process parameter
- Apply a guide-word
- Determine cause(s)
- Evaluate consequences/problems
- Recommend action: What? When? Who?
- Record information
- Repeat procedure (from step 2)
HAZOP Modes of Operation:
The following modes of plant operation should be considered for each node:
- Normal operation
- Reduced throughput operation
- Routine start-up
- Routine shutdown
- Emergency shutdown
- Special operating modes
A sample HAZOP process worksheet is illustrated in the below figure:
The key point here is that a HAZOP study must promote freethinking by the team members around each issue so that most possible problems can be identified. At the same time, the HAZOP company must impose enough discipline to keep the study moving along without wasting time on issues that are of no consequence.