Abstract: In the presented model, logic relationship of system is constructed and reliability expression of system is obtained with fault tree or block-diagram before considering common cause failure. Then replacing the reliability expression with a new one which includes the effects of common cause failure. To represent common cause failure, the elements are subject to failure by Poisson failure processes that govern simultaneous failure of a specific subset of the elements. The method for calculating the reliability of system requires that a procedure exists for determining system reliability from element reliabilities under the statistically-independent-component assumption. Several examples including typical series system, parallel system and series-parallel system are given to explain how to use the model, and the results are compared with the system reliabilities not considering common cause failures. The results are consistent with the traditional qualitative analysis, which shows the validity of the model.

Key words: Common cause failure, Failure-dependence, Reliability, Reliability model, System reliability