A safety instrumented system (SIS) monitors a process for defined hazardous conditions and automatically takes action to move it to a safe state. It typically combines sensors, a logic solver, and final control elements such as valves or switches. An SIS is designed for functional safety; it is distinct from ordinary process control, although both may interact with the same plant.
In industrial environments, an SIS can reduce the consequences of equipment failures or abnormal process conditions. Cybersecurity changes can affect its availability, timing, or trusted inputs, so they should be assessed alongside the safety design and change-management process. For example, access controls or network protections must not prevent required safety actions. Defenders coordinate safety and security reviews and evaluate changes against the specific system architecture and applicable standards.