Page 202 - Dust Explosions in the Process Industries
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Case Histories 7 75
Figure 2.1 7 Part of a screw conveyor in the exploded fish meal plant showing fixing bolts.
of broken bolts and other tramp metal into the hammer mills was a fairly frequent event.
The presence of bolts in the mills created a most unpleasant noise, which warned the oper-
ators of the plant. The normal procedure for removal of bolts from the mill was to open
the 250 mm x 180 mm door in the mill chute, shown by the arrow in Figure 2.18, and wait
until the foreign metal object eventually found its way out of the opening.
Just prior to the explosion, as part of the routine during startup of the night shift, a
worker went up to the loft, where he at once heard, by the sound from the mills, that for-
eign objects had entered several of them. By means of the usual procedure, bolts were
first removed from mills 2 and 4. However, the noise of foreign objects continued, and
the source was mill no. 1. As soon as the door in the mill chute was opened, a rapidly
growing cloud of “sparks” (probably burning fish meal particles) was discovered. At the
same time, flames just below mill no. 1 were observed through a narrow slot close to the
mill. The main explosion occurred immediately after these observations had been made,
blowing the hatch off the manhole and ejecting a strong flame through the loft room and
against the roof of the building. According to the observer, the flame was bluish in color,
similq to that of a brazing lamp. This first blast was followed by a kind of whistling or
howling that moved in the direction from mill no. 1 to mill no. 4. This may have been
flame propagation from silo no. 1 via silo no. 2 to silo no. 3 through the 0.1 m x 1 m
slots at the top of the common wall between two neighboring silos. At this moment,
the witness found his way out and escaped from the loft, which was now on fire.
The explosion was also observed from the outside by two persons who just happened
to pass by. One distinct and fairly strong explosion could be heard. This was followed
by a large pyramidal flame lasting for 30-45 seconds and extending 4-5 m above the
roof of the building. The explosion was sufficiently strong to blow out windows in the
building even in other parts than the loft.