Integration of Safety Requirements in the Initial Phases of the Project Lifecycle of Hardware/Software Systems

Abstract

This paper reports on work aimed at identifying a methodology and at defining a coherent safety life-cycle to the development of systems containing software. In particular, emphasis is placed on the initial life-cycle phases, the ones in which safety problems are generally disregarded due to limited availability of information on product characteristics and due to difficulties in treating the problem from a functional point of view. The methodology was applied to a braking system of a high speed train, and takes into account principles defined in the IEC 1508 draft standard. The methodology includes systems modelling and analysis techniques integrated in the requirements phases and organised consistent with the standard IEC 1508 in order to derive software system safety requirements. It consists in the organisation of the requirements in a structured way, functional modelling of the system, deviation analysis for hazard identification, functional Top Level Fault Tree analysis to support hazard analysis, analysis of the functional criticality and identification of safety requirements.