A fuel gas leak in a partially confined area creates a flammable atmosphere and gives rise to an explosion, which is one of the most common accidents in a chemical plant. Observations from accidents suggest that some explosions are caused by a quantity of fuel significantly less than the lower explosion limit (LEL) amount required to fill the whole confined area, which is attributed to inhomogeneous mixing of leaked gas. The minimum amount of leaked gas for explosion is highly dependent on the mixing degree in the area. This paper presents a method for analyzing the explosion hazard in partially confined area with very small amount of leaked gas. Based on explosion limit concentration, the Gaussian distribution model is used to estimate the minimum amount of leak which yields a specified explosion pressure. The method will help in analyzing hazards to develop new safe devices as well as for investigating accidents.