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What is Probability of Failure on Demand means?

asked Oct 10, 2014 in Safety by odadmin (21,030 points)

1 Answer

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answered Oct 10, 2014 by michelnr (590 points)
Probability of Failure on Demand or PFD means the probability that a Safety Instrumented Function will fail dangerously, and not be able to perform its safety function when required.

IEC 61508/61511 and ISA 84.01 use average PFD as the system metric upon which the achieved SIL for a Safety Instrumented Function is defined.

PFD is related to the amount of risk reduction that is provided by a Safety Instrumented Function.