Explosibility of Nano-Sized Metal Powders

Industrial accidents in the metal processing industries are not uncommon. Some of these accidents are in the form of dust explosions or flash fires. Two of the most cited incidents in North America for combustible metal dust explosions/flash-fires have been the Hayes Lemmerz accident in Huntington, Indiana in 2003 and, more recently, the Hoeganaes Corporation flash-fire in Gallatin Tennessee in 2011. It is important to note that combustible metals can be just as energetic and hazardous as organic fuels, and in some cases like aluminum, magnesium, titanium and zirconium even more energetic. National Fire Protection Agency (NFPA) 484 is an occupancy standard which covers the mitigation of combustible metal dust explosions and fires. While this document covers the unique hazards associated metal fine dusts and powders, it does not address the risks of metal dust combustibility at the nano-scales. Part of the reasoning for this may be due to the limited amount of experimental data in this field. This current work attempts address this issue by studying the explosion severity and likelihood of several nano-scale metal dusts and comparing the results to micron-scale combustibility data. Several metal powders including titanium, aluminum, chromium and copper were studied. Preliminary results seem to indicate that explosion severity is not significantly different in the nano-scale than in the micron-scale however, the likelihood of an explosion increases significantly as the particle size decreases into the nano range. These nano-scale materials are very sensitive and can self-ignite under the appropriate conditions during laboratory testing and handling. As a result, safety precautions and procedures for the nano-scale metal dust combustibility testing are also discussed. With this in mind it appears that for loss prevention purposes, with the explosion severity not being very different between the nano- and the micron-scale metal powders, mitigation techniques used to reduce the magnitude of the explosion for micron-scale metal dusts may be applicable to the nano-scale materials as well. However, mitigation techniques in NFPA 484 and other such standards which focus on ignition source avoidance will have to be modified for nano-scale metal dusts.