Safety Instrumented Function (SIF) - Explained

What is a Safety Instrumented Function - SIF?

The term “safety instrumented function” or SIF is becoming common in the world of safety instrumented systems (SISs). It is one of the increasing number of Swords— SIS, SIL, SRS, SLC, etc.—that are coming into our safety system terminology. The definition of a SIF as provided in IEC standard 61511, “Functional safety: Safety Instrumented Systems for the process industry sector,” leaves a bit to be desired as a practical definition, and the application of the term leaves
many people confused. IEC standard 61511 defines a safety instrumented function as a “safety function with a specified safety integrity level which is necessary to achieve functional safety. A safety instrumented function can be either a safety instrumented protection function or a safety instrumented control function.” A safety function is further defined in 61511 as a “function to be implemented by a SIS, other technology safety-related system, or external risk reduction facilities, which is intended to achieve or maintain a safe state for the process, with respect to a specific hazardous event.” The standard 61511, however, uses the terms SIS and SIF somewhat interchangeably
in places.