Developing Screening Risk Evaluation Criteria for Facility Siting Vapor Cloud Explosion Hazards

The building location evaluation methodologies published in API RP 752, Management of Hazards Associated with Location of Process Plant Buildings/CMA Managerʹs Guide [1] and Guidelines for Evaluating Process Plant Buildings for External Explosions and Fires [2], provide the option of performing a "screening risk analysis". As with any risk evaluation the results should bejudged against a "level of goodness" or evaluation criteria so that meaningful conclusions can be made from the evaluation. These evaluation criteria must be developed in consideration of the hazards evaluated, the extent and purpose of screening risk analysis, and the possible scrutiny the study may receive as part of compliance audits or post-accident investigations. This paper addresses underlying conceptual issues associated with developing company-specific evaluation criteria for facility siting risk screening evaluations with regards to vapor cloud explosion (VCE) hazards. The CCPS publication suggests a range of values for individual screening risk evaluation criteria, which companies might consider using as a starting point. The CCPS publication offers, for the first time, a risk measure called "Aggregate Risk" as a tool to distinguish between risks to workers and risks to the public. Despite this guidance, the development and application of risk evaluation criteria remains an emerging science and practice. While risk issues extend well beyond facility siting problems, many companies are currently faced with spending millions of dollars to implement risk reduction measures for process plant buildings. Since all risk cannot be eliminated, a residual risk for individuals and the company, associated with occupying a building, must be identified to evaluate the appropriateness of building location. To make reasonable and defensible decisions about their buildings, companies are developing and applying risk evaluation criteria.