16 HAZOP
A hazard and operability study (HAZOP) is a systematic examination of a process to assess the hazard potential of off normal operation or malfunction of individual items of equipment and the consequential effects on the facility. HAZOP is only one of the tools used in a PRA and should be seen as complementary to other techniques, such as FMEA. The HAZOP is qualitative and aims to stimulate the imagination of participants to identify potential hazards and operability problems. Structure and completeness are given by using guideword prompts.
General HAZOP procedure
- Select component
- Take note of the Design Intention
- Select a process parameter
- Combine with a guideword to form possible deviation to normal operation
- For each deviation, identify possible causes and consequences
- Evaluate existing protections for adequacy
- Suggest suitable action to improve operability
- Continue with other guidewords and repeat
- Select new process parameter and repeat
- Select next parameter and repeat
HAZOP common guideword combinations
| Parameter/Guideword | More | Less | None | Reverse | As well as | Part of | Other than |
|---|---|---|---|---|---|---|---|
| Flow | high flow | low flow | no flow | reverse flow | deviating concentration | contamination | deviating material |
| Pressure | high pressure | low pressure | vacuum | delta p | explosion | ||
| Temperature | high temperature | low temperature | |||||
| Level | high level | low level | no level | different (wrong) level | |||
| Time | too long/too late | too short/too soon | sequence step skipped | backwards | missing actions | extra actions | wrong time |
| Agitation | fast mixing | slow mixing | no mixing | ||||
| Reaction | fast reaction/runaway | slow reaction | no reaction | unwanted reaction | |||
| Startup/Shutdown | too fast | too slow | actions missed | wrong recipe | |||
| Draining/Venting | too long | too short | none | deviating pressure | wrong timing | ||
| Inertising | high pressure | low pressure | none | contamination | wrong material | ||
| Utility failure (instrument air, power) | failure | ||||||
| Maintenance | none | ||||||
| Vibrations | too high | too low | none | wrong frequency |