In order to clarify the scenario of fires and accidents resulting from spontaneous combustion of Refuse Derived Fuel (RDF), exothermic phenomenon of RDF with water at ambient temperature was characterized by Calvet calorimeter (C 80 and MS 80), Thermal Activity Monitor and Dewar. The spontaneous combustion characteristic of RDF without additional water was examined by Thermogravimetry and Differential Thermal Analysis and Spontaneous Ignition Tester. The experimental results show the heat generation of RDF with different water content occurred instantly after additional water was added into RDF, while no exothermic phenomenon can be observed if no additional water was added into RDF at room temperature. It means that the self-heating of RDF does not only result from fermentation of RDF because of the prompt heat generation and temperature rise of RDF with water. It is possible that the self-heating of RDF results from heat of wetting first when additional water/vapor is absorbed by RDF. The further quantitative analysis for the self-heating of RDF with water/vapor should be made to explain the process of spontaneous combustion of RDF in detail. (C) 2004 Elsevier Ltd. All rights reserved.