Functional Safety for Rail industry

Functional safety ensures that the safety risks due to hazards caused by the malfunctional behaviour of railway systems are managed to an acceptable level.

Effective management of safety risks in the railway industry is a critical issue for manufacturers and operators. Rail hardware and software systems are complex and interlinked, rail components are sourced from multiple suppliers and rail development lifecycles are becoming shorter with increasing international competitive pressure.

Relevant Standards

The railway standards comprising of EN50126, EN50128 and EN50129 have been developed by CENELEC (European Committee for Electro-technical Standardization). These standards apply to both heavy rail systems, light rail and urban mass transportation.

Technical railway standards concerning Functional Safety are covering the following subjects:

EN 50126 (IEC 62278) – Reliability, Availability, maintainability and Safety (RAMS)
EN 50128 (IEC 62279) – Software
EN 50129 (IEC 62425) – System safety

Basic Technical Concepts

The EN 50126 is used for the specification and demonstration of RAMS for all railway applications. The standards describe the life cycle process for safety relevant railway Systems. A systematic process for specifying requirements for RAMS and demonstrating that these requirements are achieved is defined.

The EN 50129 defines requirements for the acceptance and approval of safety-related electronic systems in the railway signalling field. Safety-related electronic systems for signalling include hardware and software aspects. To install complete safety-related systems, both parts within the whole life-cycle of the system have to be taken into account. The requirements for safety-related hardware and for the overall system are defined in this standard.

The EN 50129 is concerned with the evidence to be presented for the acceptance of safety related systems, it specifies those life-cycle activities which shall be completed before the acceptance stage, followed by additional planned activities to be carried out after the acceptance stage. Safety justification for the whole of the life-cycle is therefore required.

For safety-related systems which include programmable electronics, additional conditions for the software are defined in the EN 50128. The EN 50128 specifies procedures and technical requirements for the development of programmable electronic systems used in railway control and protection applications of any safety implications. The standard is intended to be used for software development and the interaction between software and the system which it is part of.