Development of effective methods suppressing spontaneous combustion is one of biggest issues for utilizing abundant and valuable fossil fuels, low rank coals, more effectively all over the world. In this review report, a large number of works performed to evaluate the spontaneous combustion susceptibility of coals and to elucidate the mechanism by which spontaneous combustion take places were briefly reviewed. Progress of various sophisticated methods such as adiabatic calorimetry, cross point temperature method, pulse flow calorimetry, etc. have made it possible to predict the spontaneous combustion susceptibility of a specified coal rather accurately. Detailed studies utilizing modern analytical instruments including FTIR, XPS, ESR, and NMR have almost clarified the oxidation reaction path leading to the spontaneous combustion. It has been clarified that the formation of hydroperoxides from aliphatic C-H moiety and active radicals is the initial step of the spontaneous combustion. Decomposition of the hydro- peroxides and COOH functional groups are believed to be the following steps. Various factors such as humidity of air, oxidation history, and pyrolysis conditions in addition to inherent coal properties have been reported to affect the spontaneous combustion. Finally, the present status of several processes developed for suppressing the spontaneous combustion of low rank coals was introduced briefly.
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