What does the average failure probability PFDavg mean when requested?
Thread Content
When considering the safety integrity level SIL, there is a requirement regarding the average failure probability PFDavg, but I’m not very familiar with it. I would appreciate it if you could help me understand this. Thank you. First, let me explain my understanding: does PFDavg=10-1 mean that when an interlock action by the SIS system is required, the probability of failure is one in ten? SIL 1 (≥10-1 to <10-1) means that when the SIS system initiates an interlock action, the probability of failure is between one-tenth and one percent.
I also want to figure it out forever! Do you know the answer now?
Your understanding is correct. Put it in more general terms: it is the probability that the SIF circuit fails to engage in interlock when it should.