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PT Notes

HAZOP Practices to Avoid: Parameter-First Approach versus Guideword-First Approach

PT Notes is a series of topical technical notes on process safety provided periodically by Primatech for your benefit. Please feel free to provide feedback.

This PT Note is the fifth in a series to help you ensure your HAZOP studies follow best practices. Poorly conducted studies result in omitting hazard scenarios which may cost people’s lives and result in catastrophic property damage. It exposes companies to regulatory and legal liabilities that can cost millions of dollars.

HAZOP deviations can be generated using a parameter-first or guideword-first approach. They differ in the order in which deviations are developed and analyzed.

In the parameter-first approach, a parameter is chosen and each of the guidewords is applied to it in turn to generate deviations associated with the parameter, e.g. No Flow, More Flow, Less Flow, etc. The process is repeated for other parameters. In the guideword-first approach, the first guideword is applied to all parameters to generate deviations, and then the process is repeated for the other guidewords, e.g. No Flow, No Pressure, No Level, ... More Flow, More Pressure, More Level, ...

In the parameter-first approach, all aspects of a parameter are taken together, which provides convenience, but it is harder to get complete and imaginative coverage of design intent. Often a list of common parameters is referenced and study teams tend to move on when the list is exhausted without searching for more parameters. In the guideword-first approach, creativity may be better served as there is a greater emphasis on generating deviations from design intent.

With a careful study leader, the choice of approach is more a matter of preference or convention. The parameter-first approach is the most common for continuous processes while the guideword-first approach can be useful for procedural and batch process studies.

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