The study aims at developing a process to evaluate the impacts of the accidental emission of hazardous chemicals. The proposed process consists of four basic steps: i) identifying risks/hazards; ii) development of the worst-case scenario; iii) simulating the emission and dispersion of the toxic chemicals; and iv) assessing the severity of the impact to the people and the surroundings. It makes use of different techniques including accidental release source term, atmospheric dispersion modeling and results in the concentration and extent of the toxic chemicals in the atmosphere for either the direct evaporation of toxic chemicals as a primary emission or the dispersion of toxic chemicals as a domino effect of a fire or explosion accident. This process has been applied in a contrived case study in Ho Chi Minh City, Vietnam. In a suppositious accident of p-xylene spill from a pesticide factory, the assessment for the worst-case scenario showed that p-xylene concentration in the atmosphere could reach up to 8,882,381 µg/m3, that is higher than Protective Action Criteria for Chemicals-level 2 but far lower than the level 3. p-Xylene from the accident could disperse more than 20 km from the site, to a highly populated area with a large number of sensitive social economic object. The results of this assessment provide helpful information for the development of accidental response plan in the practical cases or supports the training for accident prevention and responses.
Keywords: AERMOD; Assessment; Dispersion; Hazardous chemical accidents.