A Safety Instrumented System (SIS) is a set of hardware and software controls for the critical process systems that is designed to prevent or mitigate hazardous events by taking the process to a safe state when predetermined conditions are violated. A SIS can be one or more SIF (Safety Instrumented Function).

Reference Definition by Aiche.org: Safety Instrumented System (SIS) is a separate and independent combination of sensors, logic solvers, final elements, and support systems that are designed and managed to achieve a specified safety integrity level. A SIS may implement one or more Safety Instrumented Functions (SIFs).

Related Definitions in the Project: The Process Safety Engineering; Engineering; CSI Engineering