This paper presents computations on the behaviour of hydrogen/air mixture clouds which would be formed by accidental hydrogen gas release from storage tanks or pipes. It deals mainly with the dispersion of the gas mixture cloud, i.e., its shape and size as function of atmospheric and meteorological conditions, release rate, release time and amount, and boundary conditions given by the physical nature of the test ground. Cas cloud shape and size were predicted using the Computational Fluid Dynamics Code FLUENT 4. The results will contribute to the improvement of the description of the risk potential associated with hydrogen releases in accidents. The modelling was made as close as possible to the pattern of the liquid hydrogen release experiments performed by BAM in the framework of the EQHHPP. These had been made between buildings in order to simulate a real accident as close as possible.