One of the worst industrial accidents in history occurred overnight on December 2-3, 1984 at a chemical plant in Bhopal, India. The plant, owned and operated by Union Carbide India Limited (UCIL), was primarily a battery company but the owners also ventured into the manufacture of carbaryl, the active ingredient in the pesticide Sevin (Shrivastava, 1987, p. 42). Many reasons for the accident have been proposed, but cutbacks in operations and the fact that the refrigeration units for the chemical storage tanks were off-line weigh heavily in the cause of the accident (Bogard, 1989, p. 3). It has been estimated that as much as 42 tons of methyl isocyanate (MIC) escaped over a matter of minutes due to an uncontrolled reaction in storage tank 610 (Lapierre and Moro, 2002, p. 270). Thermal degradation of the MIC during the chemical reaction may have resulted in the formation of cyanide gas (Kurtzman, 1987, p. 101; Shrivastva, 1987, p. 70), but this is disputed by Union Carbide. MIC is almost twice as dense as air, so the gas blanketed the ground and did not readily mix with the surrounding air. The cloud, approximately 100 yards wide (Lapierre and Moro, 2002, p. 299), spread with the prevailing southerly wind into the impoverished neighborhoods around the plant. Death estimates vary widely, from 1754 to 15,000, while estimates of the number injured range from 200,000 to 300,000 (Shrivastva, 1987, p. 65; Bogard, 1989, p. 341).
In this chapter, we will learn about factors important in the fate and transport of airborne pollutants and how to model pollutant releases such as this one, using simple concepts included in the simulator Fate ยฎ . As in our other fate and transport models, we will use continuous (step) inputs and instantaneous (puff) inputs to the atmosphere. But as we will see in this chapter, atmospheric modeling requires knowledge of atmospheric and wind conditions. Also, transport and dilution of the pollution occur so quickly that we do not usually include degradation reactions in our model estimates.