Dust explosion in a wool factory: Origin, dynamics and consequences

On 9 January, 2001, at the wool factory “Pettinatura Italiana” in Vigliano Biellese (BI), at 5:50 p.m. an explosion caused the death of three people, the injury of another five, as well as considerable damage to part of the factory.This paper reports the events leading to the explosion together with the investigation that allowed us to reconstruct the accident's dynamic.The aetiology of the accident can be traced to an unusual case of the “Domino Effect”: some electrical equipment of the lighting system caused a spark or source of heat which caused minor smouldering or flaming combustion of dust layers; the burning dust caused a cloud of dust to rise and ignite (primary deflagration); finally, the flame front of the primary deflagration ran into and ignited large quantities of dust (secondary deflagration). The explosion involved at least 400–500 kg of flammable vegetal and wool fibers, not counting moisture and inert particles. The dust was a by-product of the removal of burr from wool during the carding phase. Since large quantities of such dust were present throughout the ground floor and its equipment, it is surprising that no explosion had occurred during the previous decades. The reason for this is possibly the absence of an appropriate ignition source.