3. What is the process for evaluating the SIL of a RIS?

To estimate the SIL of a RIS, several steps are required:

• Define the FIS operating mode: on demand or continuous;

• define the equipment making up the RIS and its architecture (mostly MooN-type redundancy);

• calculate the PFD or PFH according to the operating mode of the RIS, based on the reliability data for the equipment making it up (failure rate, repair time, test period, type of architecture, etc.);

• define the maximum achievable SIL according to the architectural constraints imposed by IEC 61508 and 61511.