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PT Notes

Conducting PHA to Facilitate LOPA

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

Often, process hazard analysis (PHA) studies do not provide sufficient detail to perform Layers of Protection Analysis (LOPA) studies properly. PHAs must provide appropriate information on hazard scenarios in order for LOPA to be performed efficiently, effectively, and accurately. If a PHA is not performed properly, the PHA will need to be revised before the LOPA study can be performed. Scenario information needed to perform LOPA includes:

  • Initiating event in enough detail to assess its frequency of occurrence.
  • Hazardous event and hazard type.
    • Scenario consequence description and type in enough detail to assign an impact level.
    • Safeguards including Independent Protection Layers (IPLs) in enough detail to assign Probabilities of Failure on Demand (PFDs) and correlated with the hazardous event and hazard type.
    • Enablers (regular, time-at-risk, conditional modifiers, others) in enough detail to assign multipliers and probabilities.
    • Risk rankings that can be used in screening scenarios for LOPA.

Primatech has developed guidelines for scenario, initiating event, consequence, safeguard, enabler and general entries in PHA worksheets to help ensure PHA studies are documented so as to support LOPA.
For more information, you can contact Primatech or consult the article:

Conducting Process Hazard Analysis to Facilitate Layers of Protection Analysis, by Paul Baybutt, Process Safety Progress, Volume 31, Issue 3, Pages 282-286, September 2012


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