Abstract A mathematical model for the estimation of the toxic impact zones in case of instantaneous release of liquefied ammonia to the atmosphere is presented. The model includes the description of toxic gas inflow due to evaporation and its dispersion in the atmospheric surface layer. The model is based on the numerical solution of three-dimensional transient equations of hydrodynamics, mass and energy transfer. The modeling procedure was implemented by using FLUENT software. The model takes into account the impact of aerosols on cloud dispersion dynamics, as well as the time-varying inflow of ammonia from the pool during boiling and evaporation. A numerical analysis of the wind speed and obstacle influence on the characteristics of the toxic impact zones in case of instantaneous release of liquefied ammonia was carried out. The boundaries of ammonia impact zones were determined by the values of inhalation toxic doses. The function of vaporization rate variation during boiling and evaporation of the pool and the function of the toxic dose calculation are integrated into FLUENT code by means of user-defined functions (UDF).