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PT Notes

Risk Reduction Measures in PHA

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

A key aspect of Process Hazard Analysis (PHA) is the identification of risk reduction measures that protect against the occurrence of hazard scenarios so that a determination can be made as to whether the existing measures provide sufficient protection to ensure tolerable risk. Unfortunately, PHA practitioners do not follow consistent practices in crediting risk reduction measures as there are no generally accepted standards or guidelines for doing so. This situation leads to inconsistent studies and possibly erroneous results. Often, risk reduction measures in PHA have been called safeguards. However, the term has not been used consistently and measures claimed as safeguards can be inconsistent from one PHA study to another.

Frequently, PHA teams record any measures that provide conceivable benefits as safeguards for hazard scenarios. This practice wastes valuable team time capturing items that may not truly be safeguards, and can result in underestimating risk as teams look at a long list of supposed safeguards and assume the scenario must be highly unlikely. Furthermore, teams may assume there is no need to qualify safeguards rigorously as there are so many of them. Moreover, the larger the number of safeguards, the greater is the deterrent to qualifying safeguards owing to the effort involved.

Additionally, PHA teams may make assumptions regarding the performance of risk reduction measures without adequate justification. These assumptions may be optimistic in light of the degree to which underlying controls that support the performance of the risk reduction measures are properly implemented. In such cases, too much credit will be taken for the risk reduction measures, resulting in underestimates of risk. Not only should the applicability of risk reduction measures for specific hazard scenarios be determined by the PHA team but also the risk reduction measures and their performance should have been validated prior to the PHA.

Risk reduction measures can be classified as primary process containment, basic process control system, preventive safeguards, mitigative safeguards, and process design. Control measures, such as inspections and tests, impact the integrity of risk reduction measures. Controls are not safeguards but they do impact the integrity of safeguards as well as the BPCS, primary containment, and design.

Risk reduction measures should be validated prior to the performance of a PHA study and a Safety Requirements Specification (SRS) should be prepared for each risk reduction measure that specifies the integrity provided. Validation addresses the role played by controls in supporting the integrity of risk reduction measures and the SRS provides the basis for the PHA team to assess how much credit may be possible for risk reduction measures. The extent of the credits that can be taken for risk reduction depends on the type and characteristics of the risk reduction measures and the hazard scenarios they protect.

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

What Risk Reduction Measures Should be Credited in Process Hazard Analysis?, Paul Baybutt, Process Safety Progress, Volume 31, Issue 4, Pages 359–362, December 2012.

http://onlinelibrary.wiley.com/doi/10.1002/prs.11520/abstract

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