Finding modules in fault trees

A new method for identifying all possible modules is presented. There are two kinds of modules: (1) those whose output events are expressed by gate events, and (2) those whose output events are not expressed by gate events. The latter are logical OR or AND combinations of basic events and modules. The method requires as input only fault-tree structure data representing gate event output-input relations. The output is a hierarchical decomposition of the fault tree into modules. The order in which the modules are identified corresponds to both the hierarchy established when the gates are numbered and the order in which modules are analyzed. The method can be applied to noncoherent fault trees. Illustrative examples are given. It is demonstrated that, by modular decomposition, 100-fold reductions in computation time are obtained for a 70-gate, 67-basic-event problem