HAZOP Study Methodology
The HAZOP study is a structured and systematic technique for identifying hazards and operating problems through reviewing process drawings and/or procedures in a meeting or series of meetings, during which a multidisciplinary team uses a prescribed protocol to methodically evaluate the significance of deviations from safe and operable design intent. Identification of such deviations is facilitated by using sets of “guide words” as a systematic list of deviation perspectives. The following steps are proposed to be followed:
- Select the node;
- Define the node’s design intent and process conditions;
- Apply the first/next parameter;
- Apply the first/next guide word, which when combined with the parameter will give the deviation;
- Determine (by brainstorming) all the potential causes of the deviation;
- Agree the credibility of each cause;
- Assess the consequences of each cause;
- Assess the safeguards provided against the causes and its consequences;
- Agree any recommendation for action or further consideration of the problem (if required);
- Apply the next guide word (relevant to the selected parameter); and
- Apply the next parameter until they have all been considered.
HAZOP Process Flow
The P&IDs were systematically and comprehensively examined to identify possible hazards and potential deviations from normal operations, associated with the proposed design. Each system/node was subjected to a review using a brainstorming approach prompted by the guideword. The node is subject to a systematic and structured analysis reviewing the potential deviations from normal operating conditions to identify potential hazards and operability issues.
| Deviation | Guideword | Parameter |
| Low/No Flow | Low | Flow |
| High Flow | High | Flow |
| Reverse/Misdirected Flow | Misdirected | Flow |
| “As well as” Flow | Additional | Flow |
| High Level | High | Level |
| Low Level | Low | Level |
| High Pressure | High | Pressure |
| Low Pressure | Low | Pressure |
| High Temperature | High | Temperature |
| Low Temperature | Low | Temperature |
| Impurities/Composition | Other than | Composition |
| Instrument/Control | Suitability | Control |
| Plant Items | Operability | Operability/Maintainability |
A further general overview of the whole design using the overview deviations to be conducted after the systems are completed. Overview guidewords are presented below
| Deviation Guideword |
| 1. General |
| 2. Testing |
| 3. Toxicity |
| 4. Electrical (HA, Isolation, Earthing) |
| 5. Services required (air, nitrogen, water) |
| 6. Material of construction (vessel, pipeline, pumps) |
| 7. Commissioning |
| 8. Startup |
| 9. Shutdown (isolation, purging) |
| 10. Breakdown (power failure, air, steam, water, vacuum, fuels, vents, computer) |
| 11. Effluent / Waste (gaseous, liquid, solid) |
| 12. Noise (sources, control methods) |
| 13. Fire / Explosion |
| 14. Safety Equipment (personal, fire detection/fighting, escape routes) |
| 15. P&ID Markups |
Here is a typical HAZOP worksheet
