What is a SIF?

A Safety Instrumented Function (SIF) is an E/E/PE safety function with a specified SIL which is necessary to achieve functional safety. The objective of a SIF is that, when functioning in the correct manner, it will place the process or system under control into a safe state in the event of a potentially hazardous deviation occurring.

A SIF must be defined in two parts. (1) Required functionality in order to achieve the safe state (the actions the SIF takes to ensure the specified hazardous event does not take place) and (2) The required performance requirements quoted as integrity level (the likelihood of the safety function operating correctly – SIL).

A SIF can only be claimed as being effective by demonstration that its functionality and its integrity are both achieved.