This paper presents an extended strategy for the analysis of complex fault trees. The method utilises simplification rules, which are applied to the fault tree to reduce it to a series of smaller subtrees, whose solution is equivalent to the original fault tree. The smaller subtree units are less sensitive to the basic event ordering during BDD conversion. BDDs are constructed for every subtree. Qualitative analysis is performed on the set of BDDs to obtain the prime implicant sets for the original top event. It is shown how to extract the prime implicant sets from complex and modular events in order to obtain the prime implicant sets of the original fault tree in terms of basic events.
Remenyte-Prescott, R., & Andrews, J. (2007). Prime implicants for modularised non-coherent fault trees using binary decision diagrams. International Journal of Reliability and Safety, 1(4), doi:10.1504/IJRS.2007.016259