This paper applies fuzzy concepts to fault tree analysis (FTA), where the basic events are considered as fuzzy numbers, and shows that n-ary fuzzy AND and Operational Research OR operators are used to evaluate the possibility of systems failure. L-R type fuzzy numbers can be defined completely by a triplet (m,α,β) and the value m is also considered a triangular fuzzy number (TFN). The comparison method is based on the dominance property. By the dominance criteria, each value m is determined to obtain the optimistic and pessimistic possibilities of the system accident. The authors can extend major and minor TFNs to fuzzy FTA for better results. The goal of this paper is to replace probabilistic considerations in the FTA by the possibilistic ones and to reduce the difficulty arising from the inexact and insufficient information of the distribution functions of basic event.
