Explosive pockets of methane-air mixtures accumulate in underground coal mines and, when ignited,produce an air-blast wave that can disturb combustible coal dust on the floor, roof, and ribs. To preventexplosions, the coal dust must be continuously diluted through application of inert rock dust, usuallypowdered limestone. Application of powdered dust process creates a respiratory nuisance downwind,where miners cannot work until the dust settles. Rock dust suppliers have developed wet and foamapplied products to reduce the nuisance and limit the interruption to mining during dust application. Totest the effectiveness of these alternative dust products, researchers at the Colorado School of Mines(Mines) have constructed a full-scale explosion test drift located at the Mines Edgar Experimental Mine(Edgar) to study the dispersibility of different rock dust applications. This paper examines the use ofPentaerythritol tetranitrate (PETN) detonating cord to produce controlled air-blasts that simulatemethane-air explosions. The air blasts are generated with curtains of detonating cord that produceshockwaves with wind speeds between 30 to 70 m/s (100 to 225 fps) depending on the length of 5.3 g/m(25 grain/ft) detonating cord used. These velocities represent the minimum air speeds required to triggerpropagating coal dust explosions. Researchers have conducted 40 test blasts with various lengths ofdetonating cord. Results show the two primary waves and two reflected waves each decaying into airblastwaves with overpressures of 14 to 27 kPa (2 to 4 psi). Pressures were recorded with commercialpiezoelectric transducers and custom-built, bi-directional probes to record the total and dynamicpressures of the wind generated in the explosion. Researchers were able to generate consistent andrepeatable wind speeds and air-blast durations sufficiently similar to a methane-air explosion to studythe dispersibility of various rock dust products and application methods.
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