ABSTRACT
Evaluating safety instrumented systems [SIS] reliability has been necessary due to societal issues and legislation. The main European standard for SIS assessment is the IEC 61508 (IEC 2005) which requires determining a probability of failure on demand [PFD] for each part of the system: detectors, logic units, and actuators. The relevance of existing models (reliability equations, reliability block diagrams, fault tree analysis, Markov processes etc.) strongly depends on the quality of input data as failure rates, maintenance characteristics, and common cause parameters.
