Safety integrity level SIL is defined as a discreet level (one of four levels, defined by a norm) for assessment of requirements on safety integrity. When discussing the safety functions assigned E/E/EP to systems connected with safety, then integrity level 4 is the highest and 1 the lowest.
|SIL 1||≥ 10-5 up to <10-4||≥ 10-9 up to <10-8|
|SIL 2||≥ 10-4 up to <10-3||≥ 10-8 up to <10-7|
|SIL 3||≥ 10-3 up to <10-2||≥ 10-7 up to <10-6|
|SIL 4||≥ 10-2 up to <10-1||≥ 10-6 up to <10-5|
SIL Safety Integrity Level
PFDavg Probability of failure on demand average, this is the probability that a system will fail dangerously, and not be able to perform its safety function when required. PFD can be determined as an average probability or maximum probability over a time period.
PFH Probability of safety function failure average per hour.
The system of analyses is elaborated in the set of norms ČSN EN 61508-X, 61511-X.