Glossary
Probability of failure of the safety function

Safe failure fraction (SFF)

Proportion of the overall rate of random hardware failures in a device that results in a safety-related failure or a detected hazardous failure, i.e. detected by a diagnostic test (based on report Ω 10 – INERIS).

Aussi bon que neuf; as good as new (AGAN)

Calculation assumption used in IEC 61508-6. After each periodic test, it is assumed that the value of $PFD(t)$ returns to its initial value.

Safety Integrity Level; SIL level

IEC 61508 introduces four discrete levels whose function is to specify requirements (qualitative and quantitative) concerning...