Consideration of Cumulative Frequency of Hazard Scenarios in SIL/LOPA Review
Venkatesh S, Akshat Khirwal
Often individual hazard scenarios or scenarios in the near zone of a process section where a safety instrumented system is provided; are considered in analyzing the frequency of events that can cause a demand on the safety instrumented system. However, given the complexity in process schemes with a high level of integration between various streams and the different sections of the process, this approach may underestimate the risk levels. In this paper, some examples are presented to show how consideration of cumulative frequency of hazard scenarios can impact the safety integrity levels (SIL) derived in a SIL/LOPA (Layer of Protection Analysis) study. The paper also presents some guidelines on how this can be incorporated in a systematic manner during a SIL/LOPA review.

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