Safety Instrumented System (SIS)

Industrial/ICS 🏭 • Difficulty: premium

Definition

A Safety Instrumented System (SIS) is an independent control layer that executes Safety Instrumented Functions (SIFs) to bring an industrial process to a safe state when dangerous conditions are detected, designed and verified to a target SIL.

Examples

A refinery’s Emergency Shutdown (ESD) system detects high pressure and commands rapid valve closures to isolate a unit.
A burner management system trips fuel on flame failure to prevent an explosion.

Discover 🔎

A Safety Instrumented System is the last automated line of defense when normal control fails or hazards develop. It monitors critical parameters through independent sensors, evaluates logic against a Safety Requirements Specification (SRS), and executes final elements (valves, breakers) to achieve or maintain a safe state. SIS must be functionally independent from the Basic Process Control System (BPCS) to ensure that a control fault cannot defeat safety.

SIS vs PLC — Difference between a SIS and a common PLC

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