Examining the Potential Fire Risk from a Short Duration Pyrotechnic Event

This study originated from trying to determine the fire risk from an armor piercing incendiary (API) passing close to flammable material. Since the temperature field produced by such a device was unknown the temperature distribution within the luminous region of a flash/fireball of laboratory-made cylindrical test charges of Barium Nitrate/Magnalium (Ba(NO₃)₂/Mg-Al) mixture, similar in composition to that of an API, was measured. The measurements have been acquired with 78.7 μm (40 gauge) high-speed K-type thermocouples that have an upper temperature limit of 1372°C. It was found that even though the thermocouples could not be located closer than 20 mm from the surface of the charges without failure, temperature differences of up to 350°C were recorded above the charge to that below. Furthermore, the heat release has a significant effect on the rate at which the temperature decays away from the surface of the charge, and this characterizes its pyrotechnic effect. In addition to the temperature measurements some image analysis has shown that the luminous region of the fireball was some 17 times larger than the charge itself, but the reaction zone was only a fraction of this size. Furthermore, this reaction zone was not as symmetrical as assumed and was probably due to an irregular burning process as the combustion wave traversed the test charge.