A method originated in the United States for breaking down coal by compressed air. Air at a pressure of 10,000 to 12,000 psi (69 to 83 MPa) is conveyed in a steel pipe to a tubeor shell-inserted shothole. The air is admitted by opening a shooting valve and is released in the hole by the rupture of a shear pin or disk. The sudden expansion of the air in the confined hole breaks down the coal.