RI 5486 Influence Of Borehole Freespace On Ignition Of Firedamp By Explosives - Summary

An investigation was undertaken by the Bureau of Mines to determine the relationship between freespace and ignition probability for borehole shots. A series of experiments was concluded which covered six freespace conditions for a pemissible explosive in a 3/4-inch borehole and encompassed some 700 shots. The results were analyzed statistically. From the analysis of variance, it was concluded that the freespace means were different and that this conclusion is not impaired by possible differences in the explosives used. Within the limitation of this experiment, a definite relationship was found between the freespace and the ignition probability. Specifically, the incendivity increases with increased freespace up to a maximum; beyond this maximum there is some indication of decreasing incendivity. Further investigations are in progress to establish whether the effects of freespace on ignition probability reported here are applicable to the large test gallery, INTRODUCTION A borehole loaded with an explosive charge is a common feature of the routine gallery tests for determining the permissibility of coal-mine explosives, of Experimental Coal-Mine shots, and of the small steel cannon shots used in connection with certain research programs on the ignition of firedamp (6, 10).6/ The question of the interrelationship of freespace, weight of charge, and ignition probability of the methane-air atmosphere has been raised