Causality Diagram using Triangular Fuzzy Numbers

Fuzzy concepts are introduced to replace probabilistic considerations in the causality diagram by the possibilistic ones and to reduce the difficulty arising from the inexact and insufficient information of the distribution functions of basic event and linkage event. All events are considered as fuzzy numbers, and n-ary fuzzy AND and OR operators are used to evaluate the possibility of system events failure. Fuzzy Causality Diagram (FCD) is so effective in fault analysis, and it is more flexible and adaptive than conventional Causality Diagram. However, the shortcoming in FCD is that the result, i.e. fuzzy numbers, may go beyond interval [0,1]. A normalization algorithm was proposed to solve the problem. The research indicates that the normalization method is so practical that the result of reasoning coincides with that of conventional Causality Diagram. The research can be of considerable importance for fault analysis of complex and hazardous industrial systems.