K.L. and B.J. Kosanke
ABSTRACT: Muzzle breaking aerial shells continue to be a significant cause of serious injury for persons discharging display fireworks. The problem is greatest for manually fired displays, where the person igniting the fireworks remains in close proximity to the mortar. Over the years, many possible causes for muzzle breaks have been suggested. Unfortunately, most of these explanations are incapable of withstanding close scientific scrutiny, and there has been no published study that has tested any of the potential explanations. Without knowing the cause(s) for muzzle breaks with some certainty, it is difficult (or impossible) for a manufacturer of aerial shells to know what measures might be taken to reduce or eliminate the chance of their occurrence.
Probably the best known characteristic of muzzle breaks is that they occur almost exclusively in the largest diameter (most potentially dangerous) aerial shells. Probably at least 90% of muzzle breaks occur in aerial shells 205 mm (8 in.) or larger. This is true, even though at least 90% of all aerial shells fired are smaller than 205 mm (8 in.). Thus any theory for the cause of muzzle breaks must account for this observation. The authors hypothesize that either setback or very small fire leaks lead to the occurrence of muzzle breaks, and that the dynamics of the propulsion of fireworks from mortars and the explosion of aerial shells is such that the chances for muzzle break occurrence is greatest for large diameter shells. In an attempt to test the hypothesis, a series of measurements were performed to determine the exit times of aerial shells from mortars and the times to explosion of shells after internal ignition. Results of these measurements are each somewhat surprising; they tend to support the hypothesis and provide insight into the mechanisms of aerial shell flowerpots.
Ref: Selected Pyrotechnic Publication of K.L. and B.J Kosanke, Part 3, (1993-1994), pp 76-87
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