Probability of failure on demand of safety systems by Multiphase Markov Chains

This paper proposed an approach to model Safety Instrumented Systems (SIS). The model is based on Multiphase Markov Chains and integrates several parameters like Common Cause Failure, Diagnostic Coverage, Proof testing, etc. The basic concepts of the Markov chains applied to availability analysis are introduced and a model to compute the unavailability for a case study is presented. We show how the variation of some characteristic parameters induces significant changes on the safety level of the SIS. The proposed method ensures the relevance of the results.