Anomalies in interpreting a fault tree (comments, with reply, on `Automated analysis of phased-mission reliability´ by J.B. Dugan)

It is suggested that priority and gates for fault trees representing components in cold standby discussed by J.B. Dugan in the above-titled work (ibid., vol.40, no.1, pp.45-52. Apr. 1991) can be treated as basic events for a full tree because exact failure probability expressions are available. This permits incorporating priority and gates into minimal cuts for evaluating the failure probability for the tree, instead of introducing the components of the gate as basic events. Other issues relating to the Dugan method of treating phased missions are discussed. The author contends that the commenter´s approach is helpful in solving only trivial systems