Considerations of the recovery in 2-out-of-3 safety-related control system

Each form of recovery can be modelled as different system behaviour with respect to its state-space, therefore the recovery – either after a random hardware failure of after a scheduled maintenance – has major impact on system safety. The paper summarises theoretical background and establishes assumptions on recovery implementation into generic model of 2-out-of-3 control system. A continuous Time Markov Chain method is used to model and evaluate safety, while hazardous failure rate of the system serves as a quantitative safety measure.