The Sum of its Parts

Abstract

A safety case is a collation of the arguments and supporting evidence needed to demonstrate that an item is safe to use. Although there are regulatory and legislative requirements in some industries, and in some parts of the world, for the production of a safety case, there are few standard definitions of what should go into one. Indeed, there is no single, correct, way to prepare a safety case; but this should not be surprising, given the wide variety of applications to which they are put.

Even after consigning large quantities of evidence to referenced documents, the safety case for a complex item is often large and unmanageable. It can be made more manageable by structuring the arguments using one of the graphical methods that are now available. The result can still be unwieldy, however. This paper presents a practical way to partition safety cases that facilitates through-life maintenance of the documentation, but is also suitable for the development phase of a system.