Page 198 - Dust Explosions in the Process Industries

Case Histories 171

Potential ignition sources can result fro, “Once a combustion process enters a bucket ele-
vator, things can only get worse.”
Fortunately, in the Fonda explosion in 1980, the bucket elevator explosions did not
result in secondary explosions in the head house. Proper housekeeping could be one
reason for this.

2.4.4
LARGE EXPORT GRAIN SILO PLANT AT CORPUS CHRISTI,
TEXAS, APRIL 1981

In this catastrophic explosion, 9 persons lost their lives and 30 were injured. The mate-
rial loss was also substantial, estimated at US$ 30 million.
The probable cause of ignition was smoldering lumps of sorghum that entered a bucket
elevator together with the grain and ignited the dust cloud in the elevator. The sorghum
was being unloaded from hopper-bottom railway cars. The grain had been stored in
these cars for 30 days, and the weather had been quite warm. A fine screen had been put
over the rail dump to prevent the larger lumps of the sorghum from entering the eleva-
tor. However, smaller lumps of smoldering sorghum nevertheless probably entered one
of the operating bucket elevators and ignited the dust cloud there.
From this elevator the explosion propagated into the other elevators and eventually
broke into the head house basement, through the dust control system, spout mixers, or
the head house silos. It then traveled from the basement into a tunnel to the basement
of a large concrete silo complex, where the combustion process entered the hooded con-
veyors and found more than sufficient dust to sustain the combustion process. As it trav-
eled within this enclosure, the flame accelerated and generated a pressure wave moving
ahead of it. Approximately halfway down the basement of the silo complex, the con-
veyor hoods blew upI throwing a large cloud of dust throughout the basement. The trail-
ing flame front then arrived at this dust cloud and a very rapid combustion process
developed. This explosion then vented itself in four different directions. It blew out the
north basement wall, it went upward through the grain silo cells, westward through the
dog house, and eastward back into the head house, which eventually exploded. The explo-
sion then propagated further through the dust extraction system and into the hooded con-
veyors in the middle of the basement of the second large concrete silo complex, through
which it was channeled to the railway dump area on the north and the shipping gallery on
the south. The explosion in the basement of the second silo complex was vented through
the basement windows.
Figure 2.13 shows the silo plant just after the explosion. The entire gallery of the
nearest large silo complex was totally demolished, and some of the silo cells had blown
out along the entire length. The head house was also badly damaged.
The extensive destruction of the railway dump area is shown in Figure 2.14. The wall
cover sheets of the shelter have been shattered and blown away from the frame structure.
According to Kauffman and Hubbard (1984), the housekeeping in the Corpus Christi
plant was excellent. Therefore, the only explanation for the extensive flame propagation
is accumulation of large dust quantities inside the process and dust extraction equipment,
including the ducting.