“…The digraphbased fault-tree synthesis strategy was first proposed by Lapp and Powers (1977). Numerous other studies concerning its applications and modifications have been published in the literature (Allen, 1984;Allen and Rao, 1980;Andrews and Brennan, 1990;Andrews and Morgan, 1986;Chamow, 1978;Cummings et al, 1983;Lambert, 1979;Lapp and Powers, 1979;Shaeiwitz et al, 1977). Essentially, a digraph provides an intermediate step which gives explicit causal relationships between the process variables, human errors and equipment failures, from which the fault trees can be constructed accordingly.…”