(10b) Specific Is Better Than General: Improving Decision Making in LOPA through the Use of Plant Data

The best industry guidance on failure rates for use in LOPA comes from Guidelines for Initiating Events and Independent Protection Layers for Layer of Protection Analysis by CCPS. Or does it?

The values established in this book were often by committee consensus because the amount of failure rate data published in the open literature was sparse. The committee deliberations on these values were measured and reasonable. While these values are well accepted across the industry, in many cases they can cause concern that they are too conservative. The predicted failure rates do not appear to match the real-world experience of those conducting, contributing too, or evaluating the results of LOPAs.

Guidelines for Initiating Events and Independent Protection Layers for Layer of Protection Analysis does clearly indicate, however, that failure rates derived from actual data will provide a more accurate view of the frequency of events and therefore risk than the generic values provided in the text. This paper will review the general methodology for collection and use of plant data for improving risk estimates and will provide example applications where this approach has yielded results in risk analysis more reasonable than those predicted using generic data.