Design for Safety

The goals of the design process are usually manifold. Clearly the resulting system must satisfy its functional requirements, and will normally also have to fulfil certain non-functional requirements which might include such factors as: size; weight; cost and power consumption. When the operation of a system has implications for safety, the system will also have a set of safety requirements. These will define what the system must and must not do in order to ensure the safety of the system. These safety requirements sit alongside the functional requirements to define what the system developer must achieve. The ability of a system to satisfy both its functional and its safety requirements is limited by the presence of faults within the system. Although definitions of this term vary, here the term ‘fault’ is taken to mean any kind of defect within the system. Faults may be