LIKELIHOOD of IGNITION of RELEASED FLAMMABLES: CCPS Book—Scope, Status, and Relationship to Other CCPS Books

When a flammable material is released from process equipment, the result may be a fire, an explosion, or the release may simply dissipate with no apparent effect other than a minor environmental impact. Depending on the circumstances, the probability of ignition can range from 0 to 1. For anyone performing a risk-based analysis of any type (QRAs, LOPAs, risk-based facility siting studies, or even application of a PHA risk matrix) two things are of importance?the probability the event will occur and the likely consequences if it does. Of the two, consequences have been the subject of much more extensive development work. Likelihood, however, is an equally critical input that requires objective evaluation and, to date, has had less technologically sound approaches developed. The result is that most of the methods for estimating the likelihood of ignition are rather crude, and in many or most cases not based on process industry data. As a result, it is not difficult to find situations where the probability of ignition for a given set of conditions varies widely from source to source in the existing literature. There are also some variables that are known to be important to the likelihood of ignition that have not, as of yet, been quantified rigorously. This results in uncertainty in risk-based studies, and also limits the ability of the risk manager to justify spending to reduce the likelihood of ignition. For this reason CCPS has undertaken the task of consolidating the available information on this subject, developing new sources of information where gaps exist, and preparing a book and associated CD that will advance the art and provide specific algorithms that analysts can use to better estimate these probabilities. The intended audience for the book will be Process Safety Subject Matter Experts (SMEs) involved in risk assessments and hazard evaluations. The timing of the book's release (third quarter of 2011) is intended to be coincident with the release of the revision to the CCPS book ?Guidelines for Evaluating Process Plant Buildings for External Fires, Explosions, and Toxic Releases? in order to support risk-based analyses that will be described in that reference. Using both sources, SMEs will have the tools to make repeatable and defendable risk-based decisions for siting.

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