Safety-Related Application Conditions - A Balance between Safety Relevance and Handicaps for Applications

Railway standards prescribe the use of Safety-related Application Conditions (SACs). SACs are demands to be observed when using a safety related system or a sub-system. The use of SACs can, however, easily be associated with difficulties. SACs of sub-systems can imply high efforts regarding their fulfillment at system level. Furthermore, SACs at sub-system level may become very obstructive for the user of the sub-system, if the safe application on system level has strong restrictions. Additionally, a large number of SACs may be very difficult to manage. In this way, SACs may obstruct the introduction of a system or a sub-system into the field. Particular hazards could arise from SACs, if they are formulated ambiguously, so that the originally intended safety-related measures are not taken at all. This paper presents the objectives and benefits of SACs and depicts difficulties and challenges associated with the use of SACs. The paper not only explains what should be the SAC content but also the quality criteria, the conditions for SAC creation and SAC fulfillment are described. The SAC management process introduced at Thales Rail Signalling Solutions GmbH is outlined. On the one hand, this process shall support the quality of SACs and on the other hand reduce the effort for SAC creation, fulfillment and evidence.