ewline"> Dispersion of heavy gases is considered to be more hazardous than the passive ones because it takes place more slowly. When the gas is accidentally released at ground level or where there are many obstacles in the area it is considered to be a heavy gas. In this paper, based on the extensive experimental work of McQuid and Hanna, the model was tested against two types of experiments: A simple experiment “Thorney Island” and a complex experiment “Kit Fox” in order to validate CFD code. In order to accomplish this validation the multiphase approach was employed. Also, the vertical temperature gradient in the atmosphere was investigated. The investigation of wind speed was done taking factors such as time, height and direction into consideration. In order to reduce the number of elements in the computational domain, a combination of 2D and 3D geometry was utilized. The results showed that the wind inlet correction, as well as the temperature gradient, had a significant influence on gas concentration records.