Calculating exact top-event probabilities using ΣΠ-Patrec

In this paper a method for calculating top-event exact probability is presented. The method combines the ΣΠ algorithm of Corynen and the pattern recognition scheme of Koen et al. The PC-based program that is based on this method is called ΣΠ-Patrec and computes the exact probability of the top-event of a system fault tree model as defined by its cut sets. The ΣΠ module of the program partitions and disjoints the cut sets and solves the resultant sub-models recursively. The pattern recognition module of the code reduces the computational complexity by recognizing repeated sub-models in the calculation process and thus avoiding repeated evaluations. ΣΠ-Patrec can evaluate both coherent and incoherent fault trees. The input to ΣΠ-Patrec is a collection of cut sets in disjunctive normal form and need not be minimal. The description of the algorithm is presented through an example problem. The results of several experiments with large accident sequences are also presented.