11. The Standard IEC 61508 and Its Safety Life Cycle

The international standard IEC 61508 on functional safety of electrical/ electronic/ programmable electronic (EEPE) safety-related systems describes a procedure to develop safe systems. It claims to be applicable to all systems that contain safety-related EEPE systems and where the failure of such EEPE systems causes significant risk for humans or the environment. As generic level A norm, it has to be adapted to the application domain. This can be conducted using existing application level B or C standards or, if they are not (yet) available, by informed application of the generic standard to a new domain. The efficient application of functional safety to advancing and new technology domains is key for successful products and short time to market. The chapter describes the standard IEC 61508 starting with a brief summary how the standard was developed and its updating history. The names of the different parts of the standard and a scheme to describe the general structure are provided. After recalling definitions and concepts from IEC 61508 that were already introduced in the textbook, it adds selected further terms, e.g., equipment under control (EUC), safety-related system, complexity of a component (type A and B components), and hardware failure tolerance (HFT) as well as a formal definition of safety function in terms of its qualitative and quantitative properties. This allows to transfer the functional safety approach to domain where reliable (active) functions needed to be realized using EEPE systems. It introduces the functional safety life cycle with its 16 phases by giving a summary of the objectives, inputs, and outputs of each phase. For each phase, sample methods are given to fulfill their requirements, in particular, such methods that are covered within the textbook, e.g., for the determination of safety integrity levels (SIL). To this end, also an overview of the methods recommended by IEC 61508 is given and how they are linked to the V-model development processes for hardware and software of EEPE systems. Finally, the safety life cycle is characterized and compared with respect to standard development processes.