A model for heavy gas dispersion in the atmosphere

Abstract

A simple model for the dispersion of heavy and cold gas clouds is developed. The horizontal dimension of the cloud is assumed to increase due to the gravity fall of the cloud. The cold cloud is heated from below and from air entrainment. The initial entrainment velocity is assumed to be linearly proportional to the front velocity and decay as its square. The entrainment at the upper surface is estimated as for atmospheric inversions and density interfaces in laboratory flows. The model predictions are shown not to be critically dependent on coefficient variations. Experimental data on heavy gas dispersion are predicted accurately. The hazard of heavy gas clouds is predicted to be dependent on environmental conditions, particularly the roughness of the underlying surface and the mean wind speed. Under unfavourable conditions a major instantaneous release is predicted to be hazardous for hours, several kilometers from the source.