New qualitative analysis strategies in Metaprime

The fault tree analysis tool Metaprime allows reliability engineers to make, in an interactive way, exact qualitative and quantitative analysis of very complex fault trees that could not be completely treated by previously available analysis technologies. The qualitative aspect of the analysis of a fault tree consists in computing all or part of the set of prime implicants (i.e., minimal cut sets) of this tree. Particularly interesting parts of this set are prime covers which are subsets of prime implicants that are sufficient to represent all the failure combinations of the system under analysis. When the tree is noncoherent, or/and when it is a multiple-fault tree, it is often possible, but very costly, to build covers with fewer prime implicants, which allows concise representation of the set of failure combinations. This paper proposes original algorithms, now integrated in Metaprime, to generate efficiently prime covers, irredundant prime covers, and minimal prime covers of noncoherent fault trees. Experiments show that these algorithms are robust and provide reliability engineers with efficient strategies for the analysis of complex noncoherent multiple-fault trees