General systems such as production plants and aircrafts can be regarded as a phased mission system, which perform several different functions depending on their operational stage. This paper proposes a novel importance measures for phased mission systems with multiple failure modes based on Birnbaumʼs importance measures. In this paper, we assume that each component has multiple failure modes in order to analyze systems more accurately. Firstly, system accident occurrence conditions at each phase are obtained in terms of component state conditions at start/end of a phase. Secondly, by applying Birnbirmʼs measures for non coherent systems, importance measures for phased mission systems with multiple failure modes are derived from accident occurrence conditions. An illustrative example of the flight of the aircraft shows the validity and details of the proposed method.

A study was carried out to find the cause of a fire occurred in a large crude-oil tank in which five workers were killed and two injured. The fire started when the workers were scraping, using wipers having a nonconductive cover, crude oil sludge accumulated on the tank floor. In our investigative experiments, we focused on the electrostatic charge on the wipers. While scraping, a large amount of static charge was generated by the contact between the glove of the operator and the cover of the wiper, and when the operator released the wiper, the electrostatic potential of the wiper rapidly increased by electrostatic induction. When the cover was contaminated with the sludge, the potential became much larger due to the high resistive layer of petroleum wax. It was experimentally confirmed that the ignition of crude oil was possible by a spark from a wiper that was electrified during the scraping of the tank floor.