Probability of Failure Per Hour PFH

average failure frequency as 3.1.23 in the functional safety standard terminology (e.g. IEC 61508[2] or

IEC 61511[3])

Note 1 to entry: The old meaning “Probability of Failure per Hour” is obsolete and replaced by “average failure frequency”.

Nevertheless PFH is still in use to keep the consistency with the previous versions of functional safety standards.

Source: ISO/TR 12489:2013(E) Reliability modelling and calculation of safety systems. Global Standards

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