A scientific paradox--explosives that are safe for use in flammable atmospheres

Explosives used in coal mines have to be efficient in blasting rock and coal but at the same time should not ignite the flammable atmosphere that can sometimes be encountered underground. When used, the explosives are placed in drilled holes and shot in rounds, with a short delay between each shot. Because the explosive is of low power, later shots in the round may fail to detonate but deflagrate instead. Any flammable atmosphere that might be present would then be ignited. This paper describes investigations of the initiation and propagation of detonation in low-power mining explosives. Qualitative studies show how detonation can fail in the vicinity of delay detonators when the explosive is precompressed prior to detonation. Analysis of X-ray photographs of detonation waves propagating in conditions near to failure enables estimates to be made of reaction-zone shapes, densities, pressures, and particle velocities. This information is used to devise a model of the reaction-zone processes, explain why compression of the explosive can lead to detonation failure, and to assess nearness to failure.