Comparative quantitative risk assessment of railway safety devices

摘要

Railways are complex systems and currently much more effort is put into quantification of risks of changes in the system, and of new safety devices. In particular, when the risk assessment largely depends on human handling and communication between track workers and train traffic control, a more detailed analysis is required. The risk comparison approach presented in here will be illustrated for out-of-service situations of railroad tracks. The approach taken applies the following techniques: (1) fault trees are used (or developed) to provide an in-depth analysis of the technical and human failure modes. Communication errors are part of the fault tree basic events; (2) for both new and existing safety devices, the mutual differences in the branches of the fault tree are identified: some branches remain the same (or change minimally), other branches are largely different; (3) Hierarchical Task Analyses are applied to specifically identify the potential communication error modes relevant for the design phase, and to identify whether communication errors may lead to critical situations. The fault trees are validated with the results so far; (4) in the operational phase human handling is further analysed with the quantitative human error technique HEART, in order to identify erosion of work (and communication) procedures. Observations during operations are used to identify differences in types of human error with time when the application of the safety device becomes more mature; and (5) a comparative risk assessments results from the above steps in the analysis.