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The preparation mechanism for gas-dynamic fracture of outburst-hazardous coal band during an explosive effect on a coal seam is considered. The conditions for crack formation in the zone farthest from the blasthole are studied, as well as simulation of induced cracks filling with methane, which was initially in coal in a dissolved state, and estimation of the start time for crack development due to the pressure of free methane. It is found that, depending on the mechanical and diffusion parameters of coal, the start time for crack development can vary from tens of seconds to many hours. The study results can be useful in developing a theory of explosive effect on a coal seam in a set of measures to reduce the risk of sudden outbursts of coal and gas.

Considering features of wave prefracturing (microfailure) of rocks under blasting, the authors put forward a new investigation approach with the use of relations of dynamic elastic stress distribution in rocks and theory of cracks. The obtained relation to estimate prefracturing zone size in relatively solid rocks under confined explosion involves pressure of gases in explosion chamber, rock pressure, crack resistance of rocks, characteristic dimension of natural jointing (presence of defects) and deformation characteristics of rocks. It is shown that dimension of prefracturing zone in rocks depends both on natural and production factors and can differ by a few times.

The authors review water inrushes in mines as a consequence of spontaneous hydrofracturing of surrounding rocks. In the developed hydrofracture model, the fracture grows under the pressure of underground water in the area of reduction in mining-induced stresses. The model includes two criteria of fracture growth—critical extension of rocks at the fracture tip and opening of fracture throughout the length. It is found that spontaneous hydrofracturing is conditioned by natural and induced stresses, hydrostatic pressure of underground water and by mining sequence.

538 Coal beds may contain a large amount of gas, mainly methane, most of which is in the adsorbed state in coal [1]. Sometimes during the underground devel� opment of coal beds, quick uncontrolled methane release occurs rapidly (in seconds). The methane released is actively involved in the dynamic crushing of coal into small fractions with a size up to several