What is SIF (Safety Instrumented Function)?

SIF - Safety Instrumented Function

Specific single set of actions and the corresponding equipment needed to identify a single hazard and act to bring the system to safe state.

Different from SIS,which can encompass multiple functions and act in multiple ways to prevent multiple harmful outcomes.

One SIS may have multiple SIF with different individual SIL,so it is incorrect and ambiguous to define a SIL for an entire safety instrumented system.