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PT Notes

PHA Practices to Avoid - Improper Recording of Safeguards

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.

A key objective of hazard analysis studies is to assess the adequacy of existing safeguards for a process. They act to prevent the occurrence of incidents and help to protect against their consequences should they occur. That is, safeguards can address both the causes and/or consequences of hazard scenarios.

Typically, all safeguards are recorded in a single column of a PHA worksheet located after the consequences column so that the safeguards column is in a scrolling relationship with the end point of the hazard scenarios, that is the consequences column. This practice means that some safeguards in the column apply to causes and others to consequences. Sometimes practitioners use category or type attribute columns to clarify the nature of the safeguards.

Different causes may have some of the same safeguards. Also, some causes may have the same consequences and the consequences may have some of the same safeguards. Some practitioners do not record safeguards that repeat earlier ones and expect reviewers to know which ones apply from the context. Such practice is poor as it may not be obvious to reviewers that repeated safeguards have been omitted.

For example, gas detectors may be recorded as a safeguard to protect operators in a reactor room from a release due to a particular cause. The same cause may also result in public impacts. If the gas detectors are not recorded as a safeguard for the public, should reviewers assume they also protect the public? The alarm may be local to the reactor room and the detectors may not protect the public. Such ambiguities from incomplete recording of safeguards can lead to serious mistakes with decisions that are made as a result of a PHA study. Practitioners should record safeguards wherever they apply to avoid the need for reviewers to make assumptions. Worksheet references can be used to avoid the need to make repeated detailed safeguard entries.

Some practitioners misunderstand the nature of hazard and operability (HAZOP) studies and record safeguards in a scrolling relationship with deviations rather than the hazard scenarios that result from them. This practice is also poor as it misrepresents the role of safeguards in the process and does not capture the relationship between safeguards and the causes and consequences they protect against. It can also result in the omission of safeguards that protect against causes and consequences because the focus is on deviations. Deviations are used in HAZOP studies as a tool to assist in identifying hazard scenarios. They are not an end in themselves.

Practitioners should follow good practices in recording safeguards during PHA studies so that the full benefit of the studies can be realized.

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