Research and application of integrated infrared, electromagnetic and radon detection for precise identification of concealed fire sources in abandoned small coal mines

Large coalfield fire zones and abandoned small-mine fire zones are widely distributed in the surface and shallow strata of the Wuda Mining Area. These fire zones are extensive, highly concealed, and prone to reignition, making complete fire control difficult. To achieve precise identification of the location and extent of concealed fire sources, an integrated infrared, electromagnetic, and radon detection method was developed based on the detection principles of infrared thermal imaging, electromagnetic surveying, and radon measurement. A T335 infrared thermal imager, electromagnetic surveying equipment, and an FD213α energy-spectrum radon detector were used for field measurements in the area near Shaft No. 12. The acquired data were jointly analyzed to preliminarily delineate the boundary and area of the concealed fire source. Borehole temperature and CO concentration were then measured to verify the detection results, and the fire-zone location was further confirmed in combination with the layout of roadways in the No. 12 coal seam. Borehole grouting was subsequently applied to control the fire zone, and the treatment effectiveness was evaluated using gas data from a tube-bundle monitoring system and repeated radon measurements. The results show that the fire-source area delineated by borehole temperature and gas measurements was generally consistent with that identified by the integrated infrared, electromagnetic, and radon detection method. The delineated fire zone covered an area of 1 351.38 m². Four grouting boreholes were constructed, with a total grout volume of 31 140 m³. After grouting, borehole temperature decreased from 210 ℃ to 30 ℃, CO concentration fell below 0.005 5%, C₂H₆ and C₂H₄ concentrations decreased to zero, C₂H₂ concentration dropped below 0.004%, and radon levels returned to the normal range. These results demonstrate that the proposed integrated detection method can effectively identify concealed fire sources in abandoned small coal mines and provide reliable support for subsequent fire-zone treatment.