The development of initial isolation and protective action distances table for US DOT (Department of Transportation) publication, 1990 Emergency Response Guidebook

The US Department of Transportation's 1990 Emergency Response Guidebook will provide an updated Initial Isolation and Protective Action Distances Table guiding first responders during the first 30 minutes of a toxic chemical release from a transportation accident. This paper summarizes the methodology and models used to prepare that table and discusses the major technical issues that were faced in its development. The modeling carried out for the 1990 Table attempted to improve the physics of the source-term release and atmospheric dispersion. Realistic gaseous and liquid accident release scenarios were identified for each of 140 chemicals. The downwind impact was then computed for releases of each chemical from a variety of appropriate container sizes. Among the submodels used in the source-term and transport modeling were gaseous and liquid release models for the various sizes of containers, pool evaporation models, a flashing model, and an atmospheric dispersion model. A key issue for future study involves the use of the various toxicological guidelines that are presently available for the various chemicals, considering that no single exposure limit has been determined for all chemicals of interest for emergency response planning, and there is no uniform guidance by the toxicologists on the use of themore » various exposure guidelines in the presence of time-dependent exposures. 10 refs., 2 figs., 2 tabs.« less