How does the use of SIL certified equipment affect achieving functional safety for a system?

SIL is a characteristic of the safety function, it is not applicable to individual subsystems, elements or components. IEC 61508 covers all the individual components of the E/E/PE safety-related system, and these subsystems, elements and components are combined to implement the safety function which has an applicable SIL target.

Supplied subsystems and components which are quoted as suitable for a given SIL target will have to be assessed within the design and associated information to determine if the subsystems and components are in fact suitable.

Suppliers of products intended for use in E/E/PE safety-related systems should provide sufficient information to allow the entire E/E/PE safety-related system to be assessed for its integration and ensure it complies with IEC 61508 for the whole function.