Availability analysis of a generalized maintainable threestate device parallel system with human error and commoncause failures

• Published in: Journal of quality in maintenance engineering 2007-10, Vol.13 (4), p.411-432
• Main Authors: Dhillon, B.S., Shah, Aashish S.
• Format: Article
• Language: English
• Subjects: Error handling; Markov processes; Operating systems; Quality control
• ISSN: 1355-2511
• DOI: 10.1108/13552510710829498

Purpose The purpose of this paper is to study the combined effect of human error, commoncause failure, redundancy, and maintenance policies on the performance of a system composed of threestate devices. Designmethodologyapproach Generalized expressions for timedependent and steady state availability of a generalized maintainable threestate device parallel system subjected to human errors and commoncause failures are developed in the paper under two maintenance policies Type I repair policy i.e. only the completely failed system is repaired and Type II repair policy i.e. both partially and completely failed system is repaired. The Markov method is used to develop general and special case expressions for state probabilities, and system timedependent and steady state availabilities. Findings In the case of threestate devices, it is demonstrated that by increasing the number of redundant devices in parallel do not necessarily lead to the improvement in the system availability. In fact, the availability of the system depends significantly on the dominant failure mode of the devices i.e. shortmode or openmode. When comparing the effect of maintenance policies on the system availability, it is observed that the Type II repair policy does not lead to an improvement in the system availability. Furthermore, it is observed that both human error and commoncause failure independently lead to lower system availability. Practical implications This study will help maintenance engineers and reliability practitioners to become aware of the combined impact of redundancy, human error, commoncause failure, and maintenance policies on the performance of the threestate device systems. Consequently, they will make better maintenance related decisions in organizations such as oil refineries and power stations that use three state devices quite extensively. Originalityvalue Most of the past models have independently studied the effects of redundancy, human error, and commoncause failure on maintainable system made up of threestate devices. This effort is one of the first attempts to study the combined effects of all these factors in a parallel system composed of three state devices.