Reliability model for computerized safety systems

A model for reliability prediction of computerized process shutdown systems is described. Particular attention is given to the classification of component failures to ensure that all types of failures are included, and to the modeling of dependent (common-cause) failures. A dependent failure model called the multiple-error shock (MESH) model is introduced. The reliability calculation is illustrated for a subsystem, using 1-out-of-2 voting logic. Some remarks as to the overall degree of redundancy of a total system are given. The dependent-failure model itself should be applicable to quite general systems