Modeling mutually exclusive events in fault trees

Abstract

A method is given for constructing fault tree gates to model mutually exclusive events. The gates are constructed from stochastically independent events, AND gates and NOT gates. Examples are presented to illustrate the technique. If the gate construction must be performed manually, the method adds complexity to the fault tree model that may not be justified. Approximating mutually exclusive events by independent events may have little effect on computed gate probabilities. The method could easily be automated in a standard fault tree solver so that this gate construction goes on behind the scenes. This would permit users to specify disjoint events directly. The authors conjecture that the additional computational cost would be small, since the number of basic events in the tree does not increase and the new NOT gates are inserted at the bottom of the tree.