Improving System Safety Modelling in accordance to IEC 61508 by using Monte Carlo Simulations

According to IEC 61508 the assessment of the Safety Integrity Level for a safety related system requires the calculation of the probability of failure on demand (PFD). Part 6 of IEC 61508 provides formulas for redundant and homogeneous systems. In contrast to this, industrial systems are often designed heterogeneously, in order to reduce to probability of common cause failures. The paper therefore provides a comparative examination of an analytical calculation, Markov- and Petri netsimulation at a running example of a heterogeneous 1 out of 2 (1oo2)-structure. The comparison of the derivative of the corresponding analytical formula and the model based approaches underline the need of dependability engineers for more user-friendly, graphical and intuitive support.