This study considers the toxicity and flammability of emitted fuel vapor from un-ignited pools of spilled chemicals on land. It also estimates the thermal radiation levels emitted from such pools in case they catch fire. A software based on EPA dispersion models was utilized to estimate the size and location of the dangerous clouds. The 3D dangerous clouds were presented in downwind, crosswind, and vertical directions from the source of the spill. The growth and decay of the formed dangerous zones with time were also investigated. Among other input data required by the above-mentioned software, the transient evaporation rate from the spilled fuel pool and its area were determined by considering the equations of conservation of mass and energy. The study also considered the situation when the spill is followed by ignition causing a pool fire. In such a case, the main concern for impact assessment was the US EPA-specified limiting radiation levels to which humans or facilities can be exposed. Exposure to 5.1 kW/m2 for more than 30 seconds can cause 2nd degree burns while exposure to the wood charring radiation level of 12.6 kW/m2 for more than one minute can cause fatality for humans. To facilitate this analysis a fire model developed by the US Gas Research Institute was used to find out safe distances from which fire fighting personnel can work towards extinguishing the fire. The application of such techniqus to a case study of an instantaneous accidental spill from a typical mobile gasoline tanker supplying fuel to local petrol stations showed that the toxic and flammable zones may extend to downwind distances of 561m and 399m, respectively. For ignited pools, on the other hand, the dangerous zones corresponding to radiation levels of 5.1 and 12.6 kW/m2 were 199 and 120 meters, respectively. For the case study of gasoline spill from a typical storage tank in a refinery resulted in the possible formation of toxic clouds extending to about 40,000 m and 48 m in the downwind and vertical directions, respectively. The flammability zone, however, was restricted to the pool area only. For most cases considered, parametric studies were performed to investigate the effects of wind speed, atmospheric stability, and vertical height on the size of dangerous zones. An interface between the dynamic results of the dispersion software and the static data of the Doha Geographical Information System (GIS) allowed the immediate identification of the major landmarks affected by the considered accidents. This data would be of a great help in developing an emergency evacuation plan for such accidents.

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