Analysis Of An Explosion Occurred In A Wool Processing Plant

A major accident occurred in an Italian wool factory in 2001, culminating with a severe explosion, despite that wool is recognized as the most flame-resistant among the natural textile fibers. The analysis of this exceptional event suggests that, in addition to classical explosion parameters, three key phenomena related to the process jointly contributed to trigger the otherwise unexpected combustion of wool flock suspensions. The first and more important phenomenon is represented by the segregation of dust mixtures occurring during processing of textile fibers and storage of byproduct. Segregation may isolate and concentrate the lighter component of wool processing byproduct as a flammable dust. The main conclusion of our analysis is that, when performing risk assessment, sampling of all materials is a necessary step, since flammability and explosivity of raw materials may not be representative of the safety of the whole process. The second phenomenon is the enhancement of the combustion of the flammable dust layered on nets as they are subjected to cross-flow of air. The enhancement may be such as to promote transition from smoldering to flaming combustion of the dust layer. The third phenomenon is related to the interaction among the flame, the induced turbulence, dust dispersion into clouds and the layout of the plant. The combination of these phenomena promoted a deflagration of unexpected severity. In this paper, the dynamics of the explosion is analyzed in the light of the occurrence of the above cited phenomena. Purposely designed experimental tests have been performed to support the key role of segregation, formation, and ignition of the flammable cloud. Results clarify that real-world dust explosion accidents may be more severe than it could be anticipated on the basis of standard laboratory tests. A procedure for risk analysis is given to predict explosions of flocking materials.