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PT Notes

What is PHRA?

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.

Process hazard and risk assessment (PHRA) is used in the IEC 61511 / ISA 84 standard on safety instrumented systems. It involves determining:

  • The hazards and hazardous events of the process.
  • The sequence of events leading to the hazardous event.
  • The consequences and likelihood of the hazardous event.
  • The process risks associated with the hazardous event.
  • Any requirements for risk reduction necessary to achieve the required level of safety.
  • The safety functions required to achieve the necessary risk reduction.
  • If any of the safety functions are safety instrumented functions.

Thus, PHRA is equivalent to a conventional process hazard analysis (PHA) with the use of a means to assess the risks of hazard scenarios and hazardous events for comparison with risk tolerance criteria, for example, risk matrices, risk graphs, and layers of protection analysis (LOPA). Risk and risk reduction targets do not necessarily need to be assigned as numerical value.

Conditions such as normal operation, start-up, shutdown, maintenance, process upset, and emergency shutdown must be considered. Reduction in effective protection due to common cause failure also must be considered. Assumptions made during the analysis such as equipment failure rates, must be documented and the PHRA must be recorded in such a way that the relationship between the above items is clear and traceable.

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Click on the links below for information on related training courses:

Process Hazard Analysis (PHA) for Team Leaders

Advanced Process Hazard Analysis (PHA) for Team Leaders

Managing Psychological and Human Aspects of PHA Facilitation

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