Common Cause Failure Analysis—Why Interlocked Redundant Systems Fail 800631

Studies of operating experiences over the last two decades have shown an increase in the number of operating incidents attributed to multiple failures as opposed to the classical case of single failures.

This paper presents an overview of a unique approach that has recently been developed to address susceptibility of electrical control systems to combined multiple failures of components and operators. The philosophical requirement for the approach will be discussed, and insight into the evolution of the technique will be provided. The approach will be described in terms of system safety and reliability tools in an integrated mix coupled with a logical process of identifying possible causative factors for the multiple failures. The technique also identifies specific points of system susceptibility to the causative mechanisms and suggests the capability for design avoidance considerations. An example will be given to illustrate the type of electrical problems addressed.