Shall the process response time be calculated during SIL Verification and compared with the process safety time?
MSalem, I’m going to answer your question according to IEC 61511, which is the functional safety standard that applies to the process industry sector. IEC 61511 doesn’t use the term “SIL Verification,” but this term is commonly used to describe the concept design phase of a safety instrumented function. IEC 61511 calls this phase “SIS design and engineering.” It is covered by clauses 11 and 12 in the standard. In this phase, you design the SIS to meet the requirements for safety instrumented functions and safety integrity. The SRS is an input for this activity. Taken literally, “SIL Verification” would mean that you’re only verifying that the SIF design meets the specified SIL target. However, it is common that you also verify the response time during this activity (as well as other functional specifications from the SRS). Your selection of components and subsystems effects response time, and if your design doesn’t meet the requirements then you’ll have to select different components a
