Forensic Reconstruction of the Explosion that Occurred at the Cordero Flour Mill, Cuneo, Italy

Abstract

This paper contains the forensic reconstruction of a powerful explosion that occurred in a flour mill in Italy in 2007. The mill produced wheat flour and was organised over 4 floors inside a very old building. The explosion occurred just after a tanker had been loaded with flour which was to be delivered to customers. Since the truck was loaded with a slight excess of flour, a small amount was sent back to one of the silos, via pneumatic transport, through a rubber hose connected to a steel pipe. The explosion destroyed the building and killed 5 workers. Through an analysis of the collected evidence, the testimony of the witnesses and an examination of the debris, the causes and dynamics of the explosion are here described. It was recognised that the explosion was ignited because of an electrostatic arc that occurred in the pneumatic transport duct. Signs of the explosion in the duct were evident because of the deformation that was provoked by internal overpressure. The triggering discharge occurred at the joint between the hose and the pipe. The pipe deformations were coherent with calculations of an internal pressure increase according to EN 14491. The explosion propagated to a flour silo and then to the whole building through the elevator case, and resulted in many secondary explosions. The explosion dynamics are here described and the lesson that have been learned are also proposed. 1. Plant description The Cordero Mill, in which the accident occurred in 2007, was a flour mill with a production of more than 0.2 t per day. It was located in a rectangular masonry building in the town of Fossano. The building consisted of a central four storey plus a basement; the products warehouse and the offices were located in a more recent three-storey construction. The main building, in which the production area was located, was organized in four main sections, separated by brick thick walls. Access to the area was through a hoist and an internal staircase. The production area which was located in the “B” rooms, while the “A” rooms were used as floor storage areas and for the preparation of the wheat for milling operations can be seen in Figures 1 and 2, which represent the ground and the top floor of the main building.