How to Determine the Safety Integrity Level (SIL) of a Safety System

Functional safety is part of the overall safety that depends on a Safety Instrumented System (SIS), made up of equipment such as Fire & Gas Detection Systems that execute Safety Instrumented Functions (SIF). A safety function is designed to ensure or maintain a safety state of the SIS when a dangerous event occurs. Each safety function has a safety integrity level (SIL). The safety integrity level is the probability for the system to execute the safety functions required in all specified input conditions within a specified time interval. The 61508 standard details the requirements necessary to achieve each safety integrity level.