Page 188 - Dust Explosions in the Process Industries

Case Histories 7 6 1

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Figure 2.2 Damaged silo roof after the wheat grain dust explosion in Stavanger in June 1970
(Courtesy of Egil Eriksson).

Almost all the windows, except those in the offices, were blown out, as was a large
provisional light wall at the top of the head house, as shown in Figure 2.3. The legs of
all five bucket elevators (0.65 m x 0.44 m cross section) were torn open from bottom to
top. The dust extraction ducts were also in part tom open.
The source and site of initiation of the explosion were never fully identified. However,
two hypotheses were put forward. The first was self-ignition of dust deposited in the boot
of the elevator in which the explosion was supposed to start. The self-ignition process
was thought to have been initiated by a bucket that had been heated by repeated impacts
until it finally loosened and fell into the dust deposit in the elevator boot. The second
hypothesis is that the chain of events leading to ignition started with welding on the out-
side of the grain feed duct to one of the elevator boots. Due to efficient heat transfer
through the duct wall, self-heating could then have been initiated in a possible dust
deposit on the inside of the duct wall (see Figure 1.10 in Chapter 1). Lumps of the smol-
dering deposit could then have loosened and been conveyed into the elevator boot and
initiated an explosion in the dust cloud there.