A framework for specification of arming system safety functions

Safety is the primary concern in the design process of high consequence arming systems. Claims form the argument about system safety, and need to be written as atomic, correct and unambiguous statements, which are easily verifiable. To support specification of claims in such a manner we contribute: a decomposition of the currently used claim types into lower level claims, a set of template claims which fit these types and finally we introduce a framework which details the relationships between these claim types. We analysed three industry projects using our approach, unearthing subtle errors. Key findings were that claims which did not fit into the defined categories described implementation detail about the safety functions, and that necessary claims could be missed. Analysts familiar with the domain may routinely leave out claims which seem `obvious, however, this could have a detrimental impact later in the lifecycle if overlooked by designers.