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PT Notes

Risk Tolerance Criteria for LOPA

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

Many LOPA studies use quantitative risk tolerance criteria to determine if risk reduction measures are needed. Both individual and societal (group) criteria must be used to make valid determinations. Neither type of criterion alone provides a complete picture of the risk from a process or facility.

Also, risk tolerance criteria can only be derived meaningfully with reference to the overall tolerable risk for a facility. These are the types of criteria used by many regulators around the world. Additionally, the type of risk measures calculated must match the type of risk tolerance criteria used. Incorrect allocation of overall tolerable risk to hazard scenarios and hazardous events or mismatching of risk criteria and risk measures will invalidate LOPA studies and result in poor and possibly wrong decisions.

Correct use of risk tolerance criteria is especially important when LOPA is used to determine Safety Integrity Levels (SILs) to comply with the IEC 61511 / ISA 84 standard on safety instrumented systems.

For more information, you can contact Primatech or consult the article:

Risk Tolerance Criteria for Layers of Protection Analysis by Paul Baybutt, Process Safety Progress, Volume 31, Issue 2, Pages 118–121, June 2012.

http://onlinelibrary.wiley.com/doi/10.1002/prs.10507/abstract

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