An Alternative to Thermal Flux Measurements in the UN Test 6(c)

Abstract : In the United Nations' bonfire test (test 6c), thermal radiation measurements are used to determine the potential radiation hazards from transportation fires involving flammable substances. Currently, packaged substances are assigned to UN division 1.3 (propellants), if the irradiance from the bonfire test of the product exceeds 4 kw/m2 at a distance of 15 m from the fire. The irradiance is measured over 5 seconds, during the period of maximum output. For substances, the value is corrected (scaled) to a mass of 100 kg net explosive content. Thermal radiation measurements require complicated instrumentation, and are subject to significant errors introduced by wind, atmospheric attenuation, smoke obscuration, variation in source fire intensity, etc. Experience with UN test 6c, at the Bureau of Mines, indicates that the irradiance from bonfires involving typical test sample weights (10 to 100 kg) can be calculated to an acceptable degree of accuracy, from simple observations of the total burning time for the involved substance. This paper discusses this simple approach, the current thinking of the UN Group of Experts on thermal flux measurements and criteria, and the impact of substituting burn times for thermal flux measurements on the classification of substances of interest.