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Risk tolerance criteria for layers of protection analysis



Layers of protection analysis (LOPA) facilitates risk-informed decision making by allowing comparison of risk estimates with risk tolerance criteria to determine if the risk is tolerable. Various types of risk criteria exist, and it is essential that LOPA practitioners match the type of risks calculated with the type of criteria used to ensure that valid comparisons are made and sound decisions are taken. A common error is to use individual risk criteria but calculate societal risk measures, which can lead to more stringent risk reduction measures than needed. Correct use of risk tolerance criteria is especially important when LOPA is used to determine safety integrity levels for safety instrumented functions to comply with industry standards for safety instrumented systems when critical decisions on process safety are made. This article describes the type of risk criteria that should be used with LOPA and contrasts risk measures calculated with LOPA and quantitative risk analysis. The concept of a representative receptor is introduced to allow the calculation of individual risk measures as well as societal risk measures. © 2011 American Institute of Chemical Engineers Process Saf Prog, 2011