What is the criticality matrix?
Evaluation of the required SIL level of Safety Instrumented Functions (SIF) – SIL level allocation

The method consists of three steps:

• positioning accident scenarios in a criticality matrix without taking into account the existence of the RIS whose required SIL level is being assessed;

• use the acceptability criteria to determine the minimum reduction factor needed to move the scenario into an acceptable or tolerable risk class;

• deduce the minimum SIL level required for the RIS from the reduction factor.

The choice of criticality matrix is free. For example, the criticality matrix presented in the circular dated May 10, 2010 could be used.