Safety Instrumented Function – A set of equipment intended to reduce the risk due to a specific hazard (a safety loop). Its purpose is to 1. Automatically taking an industrial process to a safe state when specified conditions are violated; 2. Permit a process to move forward in a safe manner when specified conditions allow (permissive functions); or 3. Taking action to mitigate the consequences of an industrial hazard. It includes elements that detect an accident is imminent, decide to take action, and then carry out the action needed to bring the process to a safe state. Its ability to detect, decide and act is designated by the safety integrity level (SIL) of the function. See SIL.