ABSTRACT
System assurance is the application of management methods and analysis techniques to assure that the completed design meets reliability, availability, maintainability, and safety (RAMS) criteria requirements. Safety integrity level (SIL) ratings can be assigned to the safety functions of electrical/electronic/programmable electronic (E/E/PE) safety-related products. SIL may be defined as measurement of operational safety that determines recommendations related to the integrity of the safety features to be assigned to E/E/PE products. The SIL notion directly results from the IEC 61508 standard (i.e., applicable only to E/E/PE safety-related systems). The railway industry (signaling) standard EN 50129 is derived from IEC 61508 (currently in edition 2.0). As a common practice, the Comité Européen de Normalisation Électrotechnique rail safety standards EN 50126, EN 50128, and EN 50129 can be used for the assurance of railway (E/E/PE) safety-related signaling products and systems. However, as mechanical products have dominant failure modes different from those of E/E/PE products (bathtub curve), the SIL concept is not directly applicable to them and EN 50129 does not seem completely appropriate to be used for their assurance. EN 50129 also advises that an SIL rating is not applicable to be assigned to a mechanic or mechatronic product. This chapter introduces a set of relatively new European (EN ISO) safety of machinery standards for the assurance of the mechanical signaling products. The chapter argues that application of these new standards will assist system assurance professionals to evaluate and assure the RAMS requirements for the railway mechanical signaling products.
