Safety Integrity Levels, Software Levels, ...

The role that safety integrity levels (by a variety of guises) have in determining the acceptability of a safety-critical system.

A Safety Integrity Level (SIL) (or a variety of other similar terms and concepts in various safety standards) provides a means of specifying the integrity required when developing a product in order to make it acceptably safe.

A Safety Integrity Level loses meaning if the relevant safety requirements do not define what is required of the system.

A large number of references to SILs are in safety-critical software, where the SIL plays a part in translating a quantitative goal into qualitative goals, usually changing product requirements into process requirements. This is mostly due to difficulties in analysing or testing complex systems (usually software) to the point where valid and useful quantitative statements can be made, instead relying upon evidence of adequate development processes.