A simplified Markov-based approach for safety integrity level verification

Abstract

Safety integrity level (SIL) verification is a critical step in the life cycle of safety instrumented systems (SIS). For the chemical process industry (CPI), SIL verification often means calculation of average probability of failure on demand (PFDavg) of a SIS. Markov analysis covers most aspects of the quantitative safety evaluation and shows great flexibility. However, for a complex SIS, the model building is so cumbersome that industrial users always try to avoid using it. A simplified approach by conducting Markov analysis on each channel of a SIS with any type of architecture and combining the results together is proposed in this paper. A case study is performed and the results prove that the simplified approach can simplify Markov modeling without loss of accuracy if a proper common cause failure (CCF) model is adopted.