Abstract
Applying a quantitative approach, this paper demonstrates the results of LSIS (LSIS Co., Ltd.) Safety Integrity Level (SIL) allocation for a Train Control System (TCS). TCS is defined in this paper as the set of Automatic Train Protection (ATP), Automatic Train Operation (ATO) and Computer Based Interlocking (CBI). SIL allocation is performed for these constituent subsystems of TCS. Systematic approaches for SIL allocation widely used in railway applications are compared in terms of the quantity of allocation results. The quantitative method, based on a risk matrix and the relationship between Tolerable Hazard Rate (THR) and SIL, is more credible than the qualitative method, in the sense that it utilizes more information (e.g., risk reduction factors involved in hazard occurrence) than the qualitative method, which purely depends on the configuration of the Risk Matrix Graph. Based on the principles of the quantitative method, the SIL allocation process is performed for the subsystems composing TCS. In conclusion, total hazard was verified such that THR is fulfilled to the corresponding SIL level, which was allocated to each function of ATP, ATO and CBI through quantitative Fault Tree Analysis (FTA) for TCS. THR allocations of each hazard are verified based on calculated failure frequency of the top event. This study has been able to enhance the reliability and safety of TCS under international standards.
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