Abstract:The purpose of this paper is to evaluate the extend of the threat zone of two mobile accidental atmospheric releases of chlorine and butane on the I-95 Highway by estimating the downwind dispersion of the chemical plumes using the numerical model ALOHA (Area Locations of Hazardous Atmospheres) and by graphing the boundaries of the threat zone using MARPLOT (Mapping Application for Response, Planning, and Local Operational Tasks). In addition, to assess the risk of exposure at two points of interest from the chlorine accident, and to measure the extent of the flammable zone; the area where a flash fire or a vapor cloud explosion could occur at some point after the release begins, resulting from the butane accident. Moreover, the aim is to study the stability class effect on indoor and outdoor concentrations and its effect on distance of the flammable zones. The paper conclude that the stability class has a significant effect on the prediction of the size of the toxic threat zone under different atmospheric dispersion conditions. In addition, the size of the area impacted after a chemical release depends on the characteristics of the chemical along with the meteorological and atmospheric conditions.