Accident Occurrence Conditions in Railway Systems
Volume 3, Number 1, January 2007 - Paper 9 - pp. 105 - 116
TAKEHISA KOHDA1 and HIROSHI FUJIHARA21Dept. of Aeronautics and Astronautics Graduate School of Engineering, Kyoto University Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan
2Railway Technical Research Institute, 2-8-38, Hikari-cho, Kokubunji, Tokyo 185-8540, Japan
(Received from the Guest Editor on July 31, 2006)
The loss caused by railway accidents becomes larger as their technology advances such as the increase in the transportation capacity and speed. In Japanese railway history, most of the safety measures were devised after suffering severe railway accidents. This kind of retrospective approach to the safety cannot be effective for the development of a new railway system, and thus a proactive system approach to the safety problems such as PRA (Probabilistic Risk Assessment) is to be desired. Toward this goal, the identification of accident occurrence conditions leading to a severe accident is essential at the design stage. This paper tries to apply the concept of "safety control functions" to the evaluation of accident occurrence conditions in a conventional event tree/fault tree approach. A safety control function is composed of detection, diagnosis, and execution functions, each of which corresponds to a specific component function or human operator action. Using safety control functions, not only the event tree for a specific initiating event can be easily constructed, but also the failure probability of a safety control function can be evaluated systematically. A simple illustrative example of a collision accident in a single track railway shows that this approach is both easy to understand and adaptive to the situational change.
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