Quest Defining Worst-case Releases for the Epa’s Risk Management Program

The Environmental Protection Agency has proposed regulations that outline risk management program guidelines. The intent of these guidelines is to reduce the number and magnitude of accidents involving hazardous materials. The proposed regulations will require all facilities that process or store flammable or toxic materials in quantities greater than specified thresholds to register with the EPA, perform hazard assessments, and submit publicly available risk management plans (RMPs) to federal, state, and local authorities. The offsite consequence analysis portion of the hazard assessment has been criticized for its definition of worst-case releases. The current proposal by the EPA (supplemental rule, March, 1995) defines the worst-case release as a release that fully depletes any hazardous material inventory in ten minutes. This approach oversimplifies the complex process involved in an actual release, and has the potential to severely underestimate or overestimate the extent of a specific hazard. This paper examines the issue of defining release rates, and illustrates how this definition can affect the outcome of the consequence analysis. The need for more sophisticated methods is demonstrated by calculating hazard zones for several ammonia storage system release scenarios. Results of this analysis show that the ten-minute spill duration may be appropriate for some cases, but is clearly inappropriate for others.