Gaps in Toxic Industrial Chemical (tic) Model Systems

There are concerns regarding the hazards to the public due to the releases of toxic industrial chemicals (TICs) to the atmosphere as a result of accidents or intentional acts. For recent chlorine railcar accidents, where 30 to 60 tons of pressurized liquefied chlorine were released in rural areas, the number of casualties estimated by several widely-used model systems far exceeded the number of casualties observed, raising concerns by decision makers about the accuracy of the model systems. The comprehensive model system consists of a scenario definition, a source emission model, a transport and dispersion model, an exposure model, and a health risk model. A few of the deficiencies or gaps in the model system are summarized in this paper, including 1) incomplete knowledge of the scenario, 2) uncertainties in the state-of-the-art of source emission models, 3) inadequate transport and dispersion models, 4) limitations of knowledge concerning the population and their movement, and 5) biases and uncertainties in health risk models.