In the Great East Japan Earthquake on March 11, 2011, large amounts of disaster waste were generated by the earthquake and subsequent tsunami. Much of the mixed wood waste was stored in a temporary storage facility for an extended period of time, and fire broke out due to spontaneous ignition. Consequently, it is now the practice that when a metropolitan epicentral earthquake occurs, disaster waste will be generated and stored locally. Fire caused by the same type of spontaneous ignition is a grave cause for concern. Thus, in order to prevent such fires, we evaluated the thermal behavior of the oxidation heat of the wood that was believed to be the cause of the heat generation in disaster waste. As a result of studies using TG-DTA and TAM, it was revealed that the thermal danger of wood increases due to increases in the temperature and in the concentration of unsaturated fatty acids in the wood. It is thought that the oxidation heat of the unsaturated fatty acids contained in the waste wood contributed to heat generation near 70 A degrees C after heat generation by fermentative bacteria.