A Safety Function is the action of a collection of equipment to implement automatic mitigation of a particular hazard. It is the job of the Safety Instrumented Function (SIF).

Some examples of common Safety Functions: 

• Car brake stop
• ESD valve – Shutdown process
• Sprinkler system 
• High pressure in a vessel opens a vent valve
• Guard sensing/speed sensing functions
• Coolent valve - Open 
• Overflow sensing functions

An example of a safety function is shown below. Note: The Basic Process Control System (BPCS) is also shown in green, where the safety function is highlighted in orange.