EN 50129 is specifically dedicated to electronic security systems, especially for signaling in railways, tramways, trolley buses and subways, but its use is more general and, de facto, it is the standard for electronic and telecommunication systems, used in  safety-critical applications in the field of public transport.

HINTSW - T & T Systems, for any SIL level, is able to support its clients in the definition of the most suitable HW architectures to meet the requirements of EN 50129 related to fault tolerance, including the proper identification of failures and compliance with the time of reaction necessary to force the safe state of the system. HINTSW - T & T Systems is also able to carry out the analyzes and calculations necessary to establish the effects of single and multiple faults, to ensure the independence of the units from the physical and internal and external functional influences, and analysis of, common mode, failure

In Appendix B (Annex B, prescriptive) of EN 50129 are given a set of concepts, definitions and requirements related with the fault tolerance of hardware systems. Primarily the effects to single faults are analyzed is introduced and the principle, known as intrinsic safety, in compliance with which the SIL 3 and SIL 4 levels systems must remain in safe conditions in the presence of any single hardware random failure It considered possible. EN 50129 indicates three different techniques to realize this principle:
  • compound safety;
  • sicurezza reactive safety;
  • intrinsic safety.

The first two techniques require the use of at least two separate units while the third allows the use of a single unit, to the condition however that it is possible to demonstrate that all of plausible unit malfunction modes are not dangerous. If more than one unit is used it is necessary to demonstrate their independence considering both the physical and functional internal influences, and the physical and functional external influences that can cause loss of independence among the units.

EN 50129 also analyzes the effects of multiple failures. The standard requires that all multiple faults must be detected that may constitute a hazard, either directly, or in combination with other additional faults, and that must be forced to a safe state in a sufficiently short time to meet specified safety objective. The standard requires that appropriate methods must be used, for example, the fault tree analysis (FTA), to determine the effects of multiple faults, and that it requires and the techniques used for their detection and for the denial of multiple failures in the predetermined times , including the supporting calculations, are documented. The standard also requires that a common mode failure analysis (CMF), is carried out, to ensure that a multiple fault can only happen due to a combination of individual random failures, and not as a result of a common mode failure.

The standard, finally, lists some suitable hardware architectures for fault detection and for the keeping of the system security state


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