To obtain fundamental data on the suppressive effect of nitrogen injection against spontaneous combustion in coal mines, experiments were carried out using intermediate scale model coal seams in a test gallery. The upper limit of oxygen concentration to suppress combustion was about 5% in the early heating stage, and under 1% in the growing stage. Temperatures in model seams during nitrogen injection dropped rapidly according with the decreased rate of oxygen concentration. Early extinguishment can be expected with lower oxygen concentration in the sealing area. Gas composition in the sealing area has a relation with temperatures in the coal seams under suppression conditions.
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