Our article "The Safety Instrumented Function: An S-Word Worth Knowing" from September 2009 has resonated with our readers over the years. This is one of our timeless pieces that gets read month after month by you and your peers.
When first published, we said that the term "safety instrumented function" or SIF was becoming common in the world of safety instrumented systems (SISs). Yet many automation professionals felt confused as to what the term really meant. The IEC standard 61511 defines SIF as "Functional safety: Safety Instrumented Systems for the process industry sector." The standard deffined a safety function 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 part that confused our readers and industry professionals with this deffinition is that the standard 61511, uses the term SIS and SIF somewhat interchangeably in places.
Read the full article to better undersdant other definitions of SIF that may make things a bit more clear.