Frequently Asked Questions

Why is a safety loop that has one manual Push button and one final valve not subject to SIL assessment in exSILentia?
Last Updated 4 months ago

In the example safety loop, one can only determine the reliability of the push button to safety valve. If you want to determine the achieved Risk Reduction of this loop you will need to include the performance of the human operator. At that point the function is no longer instrumented only and would not qualify as a SIF. When determining the achieved Risk Reduction of a loop including a human operator, the performance (read probability of failure) of the operator is typically dominant, i.e. PFD = 0.1 for the operator that determining how “good” the push button and safety valve are becomes irrelevant.

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