Assessment of Acute Exposure Dose for Emergent Phosgene Spill

Abstract

The definition of exposure dose is introduced, based on the shallow model for dense gas dispersion. The concentration of diffusion is converted into exposure dose model. The relationship between exposure dose and downwind distance is discussed, in order to describe the impact of meteorological conditions and spill parameters with a real case of phosgene spill. The curves indicate that with a small amount of leakage and the steady meteorological condition, the peak of exposure dose occurred at few meters away from the source. The results are compared to the acute toxic threshold values of phosgene, and the concerned area is defined. With the fast development of chemical industry, there are more and more hazardous chemicals in the process of transportation, storage and production. The frequently occurred accidents brought by the hazardous materials, the leakage of poisonous chemicals for instance, often bring immediate casualties. Consequently, it is of great importance to discuss the acute health risk of urgent accidents. In this article we discuss the health risk based on the leakage of toxic gas. Health risk analysis generally composed of four steps, hazard identification, dose-response assessment, exposure assessment and risk characterization, in which the most important and fundamental step is exposure assessment. The exposure assessment of emergent accidents will support the plan for evacuation and allocation of emergency resources, at the same time, the result of exposure assessment can provide the direction of improvement for the policy-makers. For exposure assessment, there are three types of measurements to characterize the exposure level, concentration, exposure dose and internal dose. Exposure concentration of toxic gas can be evaluated through mathematical models, environmental monitoring or numerical simulation. Based on the exposure concentration, factors such as exposure duration, frequency, and absorption coefficient can be introduced, to calculate the exposure dose and regarded as the result of exposure assessment. Further, through biological detection or physiologically based pharmacokinetic (PBPK) theories, the internal dose, which is the dose of toxic materials remaining in human body through metabolism, can be evaluated as the measurement of exposure. For the exposure assessment of emergent release of toxic gas, since the gas may change significantly in time and space dimensions, it is necessary to utilize the diffusion model based on the dispersion theory to determine the spatial distribution of specific material and its trends over time, and then calculate the corresponding exposure level. In this article, a specific diffusion model is selected and the measurement of exposure level is defined, to characterize the exposure level in terms of exposure dose, which is computed based on the diffusion model.