Leaking of flammable gas in a confined space creates a flammable atmosphere, giving rise to a potential explosion. Accident analysis suggests that some explosions are caused by a quantity of gas significantly much less than the lower explosion limit amount required to fill the whole confined space, which might be attributed to inhomogeneous mixing of the leaked gas. The minimum amount of leaked gas,for an explosion is highly dependent on the degree of mixing in the confined space. This paper proposes a metbod for estimating the minimum amount of flammable gas for explosion, referred to as the Gaussian distribution explosion model (GDEM). The GDEM assumes Gaussian distribution of flammable gas along the height of an enclosure, combustion of gas within flammable limits, and adiabatic mixing in the enclosure. The predicted gas volume for an explosion is tied to the explosion pressure that results in a given building damage level, The results can be applied to estimate the minimum amount of flammable gas and ventilation rate to mitigate the explosion hazard. The GDEM shows that only a very small amount of gas remaining in the confined space may result in a serious gas explosion accident. The results could be applied not only to set the leaking criteria for developing a gas safety appliance but also to determine the ventilation rate and investigate gas accidents under certain conditions. (C) 2004 American Institute of Chemical Engineers Process.