Abstract: In order to reasonably determine the β factor value required by the β factor model used for analyzing failures in a system and improve the accuracy of the analysis results, a common cause failure analysis method based on UPM was worked out. For working out the method, a system fault tree model was built to obtain the structural importance values of basic events, and to determine the common cause component groups. Then, a system fault tree model containing common cause failure basic events was built and the key common cause failure components were obtained by using the screening analysis method. The β factor values of the common cause components were determined by using UPM to calculate the failure probabilities of the key components and the system. Finally, a case of common cause failure analysis of a certain diesel engine cooling system was done to illustrate the method. Results show that the UPM-based common cause failure analysis method can be used to estimate the β factor value more accurately, and that the method can make an accurate analysis of the influence degree of each of common cause failure basic events on common cause failure of major components.

Key words: common cause failures, unified partial method(UPM), β factor value, reliability, fault tree, diesel engine cooling system