Abstract
AbstractThe influence of the dangerous undetected failure rate, ƛdu, on safety instrumented system (SIS) design has evolved over last 30 years. Now, ƛdu has a significant impact on the SIS design. Using unrealistically low ƛdu can lead to an unsafe SIS design and thus compromise the plant safety. This paper explains some of the reasons why some published ƛdu could be unrealistically low. To address this challenge, ISA TR84 committee Working Group 02 has undertaken an effort to develop a failure rate credibility assessment tool. In this tool, the user will answer a series of questions, and the weighted score of answers will provide a credibility rank for the published device failure rate. This paper will explain the approach of this tool, its target users, and its benefits.
Published Version
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