A major component of the United States Environmental Protection Agency's 112(r) Risk Management Program Rule is the evaluation and control of potential public exposures to toxic chemicals. The rule requires identification and evaluation of a worst case accidental toxic release scenario, but provides for the inclusion of passive mitigation systems in modeling the dispersion hazard zones that are to be communicated to the public. These passive mitigation systems can be taken into account in the consequence modeling if they will withstand the initiating event that causes the accidental release and function as intended.

This paper discusses several passive mitigation systems that can be designed as an integral part of storage or processing of highly toxic chemicals. These include, but are not limited to, optimizing storage conditions, design of secondary containment, toxic vapor generation control, and enclosure design. The effectiveness of various passive mitigation systems is evaluated using consequence modeling for case studies involving highly toxic chemicals such as phosgene, chlorine, and ethylene oxide.