A mathematical model to calculate the dimensions of toxic impact zones due to evaporation from the aqueous ammonia emergency spill surface is presented. The mathematical model is based on the numerical solution of mass, momentum, species, and energy transport equations. The computational procedure was implemented by using FLUENT program. The special feature of the model proposed in this manuscript is the ability to calculate simultaneously both binary solution pool evaporation and gas dispersion. The evaporation model takes into account the nonstationarity of pool evaporation process due to changes of liquid composition and temperature. The additional equations were implemented in FLUENT program by means of user-defined functions (UDF). A numerical analysis of the wind speed and obstacle influence on the evaporation characteristics and toxic dose distribution is carried out. (C) 2013 Elsevier Ltd. All rights reserved.