Safety instrumented system SIL calculation: Linking HAZOP and LOPA is easier than you think

摘要

Although a hazard and operability (HAZOP) analysis identifies failure events or upsets and the severity of the outcomes by engaging knowledgeable plant personnel, the process typically provides only qualitative information about event frequency and mitigated frequencies. This helps plants make decisions for safety improvement, but does not provide the detailed information necessary for a safety integrity level (SIL) determination. The layer of protection analysis (LOPA), on the other hand, is a means to analyze event frequencies and the mitigating effects of protection layers. It does not provide a process for identifying possible failures in the plant and the severity of their consequences. This article shows how the two activities can be easily linked to provide the information required for a safety integrity level determination for a safety instrumented system (SIS), according to the recommendations of ISA-84.00.01 (IEC 61511 Mod).