Page 197 - Dust Explosions in the Process Industries

170 Dust Explosions in the Process Industries

Figure 2.12 Damaged bucket elevator following a corn dust explosion in a grain terminal at Fonda,
Iowa, 1980 (Courtesy of C. W. Kauffman, University of Michigan).

clamp and the grounded elevator casing. The hot spot either ignited the corn in the ele-
vator boot, which in turn ignited the corn dust cloud or the dust cloud was ignited directly
by the hot spot.
The explosion was transmitted to a second bucket elevator and blast waves and flames
propagated upward in the legs of both elevators, bursting the casings. Figure 2.12 shows
one of the elevator legs after the explosion.
Kauffman (1982) emphasized the essential role played by bucket elevators in 14 care-
fully investigated grain dust explosions in the United States. In 5 of the 14 accidents, the
explosion originated in the bucket elevator. In six other accidents, bucket elevators were
able to effectively amplify and propagate the explosion, although the combustion process
did not originate there. Only in 3 of the 14 cases, the bucket elevators were not involved.
Kaui%nan (1982) also discussed why the bucket elevator is so frequently involved in the explo-
sions. When in operation, the elevator contains an explosible dust cloud that is confined.