Toward an Application Guide for Safety Integrity Level Allocation in Railway Systems

This article describes the development of an application guide for safety integrity level (SIL) allocation in railway systems. The guide is based on feedback and comments from various railway stakeholders about their practices of SIL allocation to railway safety-related functions. The authors have updated basic methodology used for SIL allocation to include railway rolling stock safety-related functions. The updated methodology is based on the flowchart formalism used in common safety method (CSM) European regulations. Components include quantitative safety requirements, tolerable hazard rates (THR), last safety weak links, functional dependencies, and technological complexity. The authors contend that use of this standard methodology can mitigate problems that arise when different methods are used by different countries or entities to allocate SIL (based on standards in use, national practices or regulations, project and operator methods, or available data). The authors demonstrate how this methodology can be applied through the example of “emergency brake” subsystems. Some specific SIL allocation rules are also defined and illustrated. The authors describe how SILs can be used within the present-day harmonized risk management process for railway systems in the European Union (EU).


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  • Accession Number: 01682903
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Aug 9 2018 11:48AM