(72b) The Use of Overpressure Exceedance Curves In Building Siting

Compliance with the American Petroleum Institute (API) Recommended Practice (RP) 752 has become an industry standard.  Design and layout of new facilities can incorporate most of the principles and spacing requirements presented in API RP 752 with a basic consequence modeling study.  Yet many existing facilities are finding that a basic consequence modeling study indicates major problems for onsite buildings when evaluating vapor cloud explosion impacts.  The worst-case explosion scenarios, and often the “more likely” scenarios, typically show unacceptable overpressure impacts at buildings within or near hydrocarbon processing units.  API RP 752 does allow risk-based analyses.  One of the most useful forms of a risk-based study is the generation of overpressure exceedance curves.  These measures of potential impact to a building incorporate a wide range of potential explosion scenarios, and the probability of each event.  This paper will explore the construction of overpressure exceedance curves for a typical hydrocarbon processing facility, and will highlight some of the benefits, as well as some of the potential problems, of their application.