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Application & OT Security · Advanced

Safety Instrumented System (SIS)

An independent control system that brings an industrial process to a safe state when dangerous conditions are detected.

Definition

SIS functions are engineered to safety integrity levels (SIL) under IEC 61508/61511 and are meant to be separated from the basic process control system. The TRITON/TRISIS malware targeted Schneider Electric Triconex SIS controllers, showing attackers can target safety functions.

Example

An SIS automatically closes the feed valve if reactor pressure exceeds a safe limit.

Exam tip

Separation of SIS from the process control network is a key safety and security principle.

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