New gate operations of fuzzy fault tree analysis

Fault tree analysis (FTA) is a widely used method for system analysis in which a particular type of fault is expanded deductively to several causes (events) and basic causes (events) are determined. The representation of the relationship between the occurrence of an upper event and that of the lower events is called a gate operation. Here, each event occurrence is represented by Boolean variables and gate operations are based on Boolean algebra. The authors note that, in most decision-making analysis, we rely on subjective information instead of the crisp Boolean expressions demanded by FTA. Therefore, we have developed the fuzzy FTA (FFTA) using Boolean linguistic variables for the event values. The two most important gates developed for the purpose of FFTA are utilized for fuzzy mean and fuzzy sum operations