A major accident of high toxic gas, leaking of 20 tons of hydrofluoric acid [HF], was happened on 27 September 2012 in Gumi, about 200 km from Seoul, South Korea. The accident killed five workers at the site and severely injured at least 18 others, including workers and emergency personnel. The initial government response to the accident, including possible mistakes by firefighters and a sluggish evacuation of nearby residents, was sharply criticized in the Korean media. The number of industries using toxic gas also has significantly increased most of them located near inhabited areas. These facts are a huge challenge for administrations who must minimize risks around toxic gas facilities where major accidents can occur, and must provide a safe community emergency response. When toxic gas is released during for a certain time, the resident downwind area should be evacuated or stayed in a building with sealing doors and windows, and wait until the toxic gas puff has gone. The criterion for evacuating or not of residence in the building is not setup until now, which might depend on the building and meteorological conditions. In this work, we analysis the toxic gas concentration in the building with toxic gas atmospheric dispersion to help that the local communities are likely to be advised to go indoors and to close windows and doors until given further advice by the emergency manager. Wind speed and ventilation ratio of building influence highly on the concentration of toxic gas in the building.
toxic gas, indoor concentration, emergency response tree, critical distance, ventilation ratio, gas dispersion
 Lee, K., Kwon, H.M., Cho, S., Kim, J. & Moon, I., Improvement of safety management system in Korean chemical industry after a large chemical accident. Journal of Loss Prevention in the Process Industries, 42, pp. 6–13, 2015. http://dx.doi.org/10.1016/j.jlp.2015.08.006
 Parker, S.T. & Coffey, C.J., Analytical solutions for exposures and toxic loads in well-mixed shelters in support of shelter-in-place assessments. Journal of Hazardous Materials, 192, pp. 419–422, 2011. http://dx.doi.org/10.1016/j.jhazmat.2011.04.107
 Kakko, R., Effects of the ventilation system and chemical reactions on the concentration and individual risk estimates of toxic materials. Journal of Loss Prevention in the Process Industries, 5, pp. 145–152, 1992. http://dx.doi.org/10.1016/0950-4230(92)80017-3
 Crowl, D.A. & Louvar, J.F., Chemical Process Safety Fundamentals with Applications, 3rd edn., Prentice Hall: Upper Saddle River, NJ, pp. 203–204, 2011.