Effects of recovery on the safety of a safety-related control system

Safety analyses of a safety critical control systems (SRCSs) are very often based on stochastic state-oriented mathematical reliability models. Behaviour of the SRCS and its responses to random failures is rather different when safety and reliability analysis is compared. This paper reflects safety analysis of the high demand systems with the focus on systematic approach to construction of valid models, with the aim for implementation of all relevant safety-affecting parameters. A special effort is put into implementation of a failure detection and recovery mechanism. Both of these factors have major impact on safety of redundant systems and their incorrect implementation usually render the safety analysis results invalid.