scope:

1.1 This Technical Report provides guidance on specific issues, listed under 1.3 below, for applying the safety process requirements in EN 50126-1 to a railway system and for dealing with the safety activities during the different system life cycle phases. The guidance is applicable to all systems covered within the scope of EN 50126-1. It assumes that the users of the report are familiar with safety matters but need guidance on the application of EN 50126-1 for safety issues that are not or could not be addressed in the standard in detail. 1.2 EN 50126-1 is the top-level basic RAMS standard. This application guide, CLC/TR 50126-2 forms an informative part of EN 50126-1 dealing explicitly with safety aspects as limited by the scope defined in 1.3 below. 1.3 Limitation of scope The scope is limited to providing guidance only for the following issues related to EN 50126-1. i) Production of a top-level generic risk model for the railway system down to its major constituents (e.g., signalling, rolling stock, infrastructure, etc.) with definition of the constituents of the model and their interactions. ii) Development of a checklist of common functional hazards within a conventional railway system (including high speed lines, Light Rail Train.s, metro.s, etc.). iii) Guidance on the application of the risk acceptance principles in EN 50126-1. iv) Guidance on the application of functional safety in railway systems and qualitative assessment of tolerable risk with examples. v) Guidance for specifying relevant functional safety requirements and apportionment of safety targets to the requirements for sub-systems (e.g. for rolling stock: door systems, brake systems, etc.). vi) Guidance on the application of safety integrity level concept, through all the life cycle phases of the system. vii) Guidance on methods for combining probabilistic and deterministic means for safety demonstration. viii) Guidance on the essentials (incl. maintenance, operation, etc.) for documented evidence or proof of safety (safety case) with proposals for a common structure for such documentation. 1.4 A diagrammatic representation of the scope and limitations of the scope cross linking with the safety activities within the life cycle phases of EN 50126-1 and the roles/responsibilities of the principal players is given in Table 1 below. However, for full comprehension it is suggested that these clauses are considered only after the whole document has been read: