A system for breaking down coal by which compressed air, generated locally by a portable compressor at 10,000 psi (69.0 MPa), is used in a releasing cylinder, which is placed in a hole drilled in the coal. Thus, slow breaking results, with no flame, in producing a larger percentage of lump coal than is made by using explosives. Its principal advantage is that it may be used with safety in gaseous and dusty mines.