SIS Factors

According to the ANSI/ISA S84.01 and IEC 61508 standards, the scope of an SIS is restricted to the instrumentation or controls that are responsible for bringing a process to a safe state in the event of a failure.

The availability of an SIS is dependent upon:

• Failure rates and modes of components
• Installed instrumentation
• Redundancy
• Voting
• Diagnostic coverage
• Testing frequency

Reference: Triconex