For reasonable explanation about recent accidental gas explosions caused by condensed phase combustibles occurred in Japan, the processes of such gas explosions have been investigated. When the combustible is of condensed phase at its initial state, gasification is necessary to form a flammable mixture causing a gas explosion. The process of gasification characterizes such a gas explosion. When the combustible is RDF (refuse derived fuel), the temperature was inferred to spontaneously increase. Also, the flammable gas should be generated within a confined high temperature region in the pile and come through a low temperature layer without combustion. The growth of a flammable layer after gasoline is spread over floor is analytically evaluated. The flame propagation through the flammable layer established over the floor enhances the pressure enough to break the structure of the office. Long-term heating is inferred to cause ignition of dried garbage, and the mechanism of flammable gas generation would be similar to that in the case of the RDF explosion. For prevention of losses at accidental explosions caused by gasification of condensed phase combustibles, understanding of the phenomena is the most important. (c) 2005 Elsevier Ltd. All rights reserved.