Atmospheric Dispersion Modeling of Reacting Chemicals

N. Albert Moussa, X. John Zhang, Daniel E. Groszmann, and Michael C. Masonjones
BlazeTech Corporation
24 Thorndike Street
Cambridge, MA 02141
(617) 661-0700

Allen B. Beach, Richard C. Crews, and Don D. Harrison
Wright Lab Armament Directorate
Eglin AFB, FL 32542-5434

Abstract
An advanced source characterization and dispersion modeling system for instantaneously released reacting chemicals has been developed and validated against available test data. The model considers the complex interaction of physical, chemical, and thermodynamic processes. The physical process includes dense cloud slumping or bouyant puff rise, cloud lift-off, and passive dispersion; the chemcial process includes reaction with ambient air with an entrainment limited rate; and the thermodynamic process includes evaporation and condensation. The model also includes several databases containing physical, thermochemical, and toxic data for a large number of species.

Three cases are presented to illustrate the comprehensive capabilities of the model. First, an explosive release of a mixture of magnesium, Teflon, Viton A, and paraffinic oil is modeled. The explosion products continue to react with air in the high temperature fireball as well as in the cooler stem underneath. Second, a spill of saturated boron trichloride, which after evaporation can react with water moisture in the atmosphere, is moeled. In both of these cases, large amounts of reaction heat are released, and the cloud temperature, bouyancy and the resulting final rise are all increased. In the second case, the initially dense cloud may become lighter than that of air and the cloud may lift off the ground and rise to a high altitude. Third, a parametric study is performed on the fireball size for the combustion of hydrocarbons with release amounts varying over several orders of magnitude. Available experimental results are used in validating the model output. The effect of exothermic heat release has the tendency to reduce the maximum ground concentration and dosage, and thus, is of particular interest to safety/environmental engineers and decision makers.

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