The extent of a hazardous area is the distance over which an explosive atmosphere may occur. The main objective of this study is to investigate the accuracy of mathematical models to determine the extent of hazardous area in industrial facilities where explosive gases are used. The accurate prediction of the extent of a hazardous area is important for both process safety and economy. Underestimating hazardous areas can lead to explosions, and overestimating them incurs unnecessary cost. In this study, the authors compared the extent of hazardous areas predicted using analytical models with those obtained from a computational fluid dynamics CFD model. The latter was verified through experiments, and successfully predicted the characteristic barrel pattern at the exit of the leaking orifice, typical of choked flow. The emission and dispersion of three flammable gases (hydrogen, methane, and ethylene) from five orifices of different diameters under different stagnation conditions were predicted. The results show that the extent of hazardous areas predicted by the analytical models was overestimated, but was accurately predicted by the CFD model. Of the analytical models tested, the models proposed in Italian Guide CEI 31-35 and by Ewan and Moodie yielded the closest results to those of the CFD model. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.