Case study: Aluminum-dust explosion

An explosion occurred in equipment that was being used to pulverize aluminum-alloy ingots, to form a powder with small particle size. In this process air was recycled through a grinder, cyclone product separator, and blower, with a side stream to extract undesired dust to a dust collector. However, the concentration of dust in the circulating air stream was above the minimum explosible concentration in most of the recycle system. Ignition of this dust/air dispersion occurred as a result of an exothermic oxidation of accumulated combustible dust in the return-air ductwork, accelerated by the relatively high temperature of the circulating air. Because the system was not protected against internal explosion, an access door on the grinder was forcibly ejected, and the door struck a hose on the liquefied petroleum gas (LPG) cylinder on a nearby forlift truck. Escaping LPG vapors-ignited by the dust fireball from the open grinder door - resulted in a flash fire that caused fatal burn injuries to the forlift driver. The primary cause of this incident was failure to adequatelv manage changes to the process. The causes and lessons learned as a result of this incident are described in detail, together with recommendations for improved practices to avoid similar events. Although they are related to this specific incident, the lessons are especiallly relevant for preventing combustible-dust explosions.