Page 195 - Dust Explosions in the Process Industries

168 Dust Explosions in the Process Industries

2.4.2
RIVER GRAIN TERMINAL AT ST. PAUL, MINNESOTA, JUNE 10, 1980

The explosion occurred just before lunchtime. There were no fatalities, but 13 persons
were injured. The material loss was estimated at about US$0.3 million.
The probable cause of the explosion was that an electrician was repairing live elec-
trical equipment in a truck-receiving cross tunnel, while the elevator was unloading
grain trucks. The ignition source probably was electric arcing in an open electric junc-
tion box located within an explosible dust cloud.
The blast and flame front moved in one direction along the tunnel into the head house
basement. There were open spouts to the bucket elevators, and with the secondary explo-
sion in the basement initiated by the cross tunnel explosion, the explosion was carried
into all the bucket elevators and the dust extraction systems. The building was of struc-
tural steel with nonsupporting metal clad walls, and this allowed rapid pressure relief by
blowing out the wall panels (see Figure 1.136 in Chapter 1). Therefore, the blast that went
out of the head house and up one of the bucket elevators did not do much damage to the
galleries. This was fortunate because, as Figure 2.10 shows, the level of housekeeping
in the gallery at the moment of the explosion was rather poor. With a stronger blast enter-
ing the gallery and a flame following, a serious secondary gallery explosion could have
resulted.
Figure 2.1 1 shows another example of unacceptably large quantities of accumulated
dust. Kauffman (1982) used this photograph as a reminder when emphasizing that even

Figure 2.1 0 Accumulation of dust in the gallery of a river grain terminal at St. Paul, Minnesota, 1980
(Courtesy of C. W. Kauffman, University of Michigan).