The sensitiveness of explosives - The grit sensitiveness of high explosives

Abstract

Risks in handling various high explosives are enhanced if grit is present. Quantitative measurements o f the enhanced sensitiveness, made by means of the Rotter impact machine, have included tests on the high explosives: T. N. T., picric acid, tetryl, cyelonite and waxed cyclonite, and penta-erythritol tetranitrate (P. E. T. N.). In addition to the standard Rotter test on the explosives as used in practice, experimental modifications tried include the admixture of controlled amounts of grit of varying hardness and size, to the high explosives. The effect has also been tried of confining the explosives between surfaces of tin or aluminium, in place of the usual brass and steel. Additional methods of calculating the probability of explosion have been used, to distinguish between initiation and propagation. As a result of these experiments, a standard test has been specified for the grit sensitiveness of high explosives. Sensitization by grit, as measured by the Figure of Insensitiveness (F. I.) on the Rotter machine under brass and steel confinement, does not appear to occur if the grit hardness is less than 4 on M oh’s scale. With grit of hardness greater than 4, sensitization increases with increase in the weight percentage of grit. , Sensitization is normally greatest for the explosive with lowest F.I.; 1 % of various factory grits can lower the F. I. to a marked degree. Confinement of cyclonite between surfaces of low melting metals lessens sensitization by grit, but enhances normal impact sensitiveness. Comparison of the grit sensitiveness of cyclonite with that of waxed cyclonite suggests that the effect of the wax is to quench local ‘self-heating’. The results so far obtained on sensitization by grit can be explained in terms o f the production of a number of ‘hot spots’ whose temperature in the case of cyclonite and P. E. T. N. appears to be around 750° K.