Assessment Method For Failure Of A Safety Function For Safety Instrumented System

Based on the classification and analyses of factors affecting on the failure of a safety function for the safty instrumented system (SIS), the comprehensive assessment model of common cause failure factors and the accurate model of the self-diagonostic coverage by comparison are established. Based upon the probability of failure for a safety function from different period of time, the comprehensive assessment model for failure of a safety function for SIS and the spurious trip rate model of SIS are set up. At the same time, the probability of failure for redundant system composed of diverse component and the multiple voting are discussed. At the end, demonstration application of comprehensive assessment model for failure of a safety function for SIS is carried out on the pressure protection function of the simulative safety supervision system for a tank. Comparing with the results of other method and assessment software, it indicates that the systematic failure has great influence on the failure of a safety function for SIS and it is should be considered in the assessment for failure of a safety function.