This part 2 of EN 50126

• considers the safety-related generic aspects of the RAMS life-cycle;

• defines methods and tools which are independent of the actual technology of the systems and subsystems;

• provides:

– the user of the standard with the understanding of the system approach to safety which is a key concept of EN 50126;

– methods to derive the safety requirements and their safety integrity requirements for the system and to apportion them to the subsystems;

– methods to derive the safety integrity levels (SIL) for the safety-related electronic functions.

NOTE This standard does not allow the allocation of safety integrity levels to non-electronic functions.

• provides guidance and methods for the following areas:

– safety process;

– safety demonstration and acceptance; – organisation and independence of roles;

– risk assessment;

– specification of safety requirements;

– apportionment of functional safety requirements;

– design and implementation.

• provides the user of this standard with the methods to assure safety with respect to the system under consideration and its interactions;

• provides guidance about the definition of the system under consideration, including identification of the interfaces and the interactions of this system with its subsystems or other systems, in order to conduct the risk analysis;

• does not define:

– RAMS targets, quantities, requirements or solutions for specific railway applications;

– rules or processes pertaining to the certification of railway products against the requirements of this standard;

– an approval process by the safety authority.

This part 2 of EN 50126 is applicable to railway applications fields, namely Command, Control and Signalling, Rolling Stock and Fixed Installations, and specifically:

• to the specification and demonstration of safety for all railway applications and at all levels of such an application, as appropriate, from complete railway systems to major systems and to individual and combined sub-systems and components within these major systems, including those containing software, in particular:

– to new systems;

– to new systems integrated into existing systems already accepted, but only to the extent and insofar as the new system with the new functionality is being integrated. It is otherwise not applicable to any unmodified aspects of the existing system;

– as far as reasonably practicable, to modifications and extensions of existing systems accepted prior to the creation of this standard, but only to the extent and insofar as existing systems are being modified. It is otherwise not applicable to any unmodified aspect of the existing system;

• at all relevant phases of the life-cycle of an application;

• for use by railway duty holders and the railway suppliers.