A computerized fault tree construction methodology

Abstract

A new approach to automating the fault tree construction process is proposed. The methodology has features which make it applicable to binary state systems and also to process control systems. Previous attempts to model the failure generation in systems have worked well on only a small sub-class of system types and have failed to produce a generally applicable method. Thus in some previous approaches there are desirable features which are worth retaining in a new construction method. The new method is based on the flexibility of the decision table method but incorporates a way of detecting, classifying and analysing control loops, similar to that used with operators in the digraph approach. As well as using operators to deal with control loops a new operator is introduced that deals with two-state circuits. This will mean that when constructing the fault trees, the difficulty of handling repeated events will be eliminated and the size of the tree structures will be significantly reduced. The developed algorithm can produce a tree format appropriate for direct input to an analysis code. The method is demonstrated in this paper by its application to a simplified safety system from the railway industry. This system has been selected as it exhibits features that are typical of two-state circuitry but is also small enough to illustrate the new developments introduced.