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PT Notes

HAZOP Practices to Avoid - Cause-By-Cause (CBC) Versus Deviation-By-Deviation (DBD) Recording

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 third 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.

In Deviation-By-Deviation (DBD) recording, scenario causes, consequences, safeguards, and recommendations are related only to the parent deviation. No correlation is provided between individual causes, consequences, safeguards and recommendations. Thus, all causes listed for a deviation do not necessarily result in all of the listed consequences. Specific cause / consequence / safeguard / recommendation relationships are not explicitly identified. It is assumed that study reviewers can infer the correlations.

In Cause-By-Cause (CBC) recording, scenario consequences, safeguards and recommendations are explicitly correlated with each particular cause of a deviation. Each cause has an independent set of consequences, safeguards, and recommendations relating to it.

The DBD approach requires less time and documentation than the CBC approach. However, the CBC approach is more precise and avoids the ambiguity of the DBD approach. While the CBC approach requires more time and lengthier documentation, it lessens the likelihood of incorrectly estimating scenario risks or crediting safeguards that do not apply. Studies should be recorded using the CBC approach.

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