Page 215 - Dust Explosions in the Process Industries

Case Histories 187

tunnel ruptured, and the resulting blast dispersed large quantities of dust in the workrooms
into explosible clouds that were subsequently ignited. From the eastern dust collectors,
the explosion also propagated into the underground flax stores. It is not unlikely that even
this scenario could be developed further in such a way as to agree with the evidence from
the seismic recording.

2.9.4
ADDlTlONAL REMARKS

The investigation of the Harbin disaster exposed the great difficulties in identifying the
exact course of events of major explosions creating massive damage. In addition to
causing pain and grief, loss of life also means loss of eyewitnesses. Besides, the imme-
diate need for fire-fighting and rescue operations changes the scene before the investi-
gators can make their observations. Also, the explosion itself often erases evidence,
such as of the ignition source. This problem was shared by the experts who investigated
the Harbin explosion, and it seems doubtful that the exact course of events will ever be
fully resolved.
However. the Harbin disaster unambiguously demonstrated the dramatic consequences
of inadequate housekeeping in industrial plants where fine dust that can give dust explo-
sions, is generated.

.I 0
FIRES AND EXPLOSIONS IN COAL DUST PLANTS

2.1 0.1
METHANE EXPLOSION IN 17,000 m3COAL SILO AT ELKFORD,
BRITISH COLUMBIA, CANADA, IN 1982

As mentioned in Section 1.5, the handling and storage of coal can, in addition to the dust
explosion hazard, present a gas explosion risk, due to release of methane from some types
of coal. An account of such an explosion was given by Stokes (1986).
The silo of height 48 m and diameter 21 m that exploded was used for storage and load-
out of cleaned, dried metallurgical coal. The capacity of the silo was 15,000 tomes.
rior to the explosion, a methane detector had been installed in the roof of the silo.
The detector activated a warning light in the silo control room when a methane con-
centration of 1% was detected, and an alarm light was activated when detecting 2%
methane. A wet scrubber was located in the silo head house to remove dust from the dust-
laden air in the silo during silo loading. A natural ventilation methane stack was also
located in the silo roof to vent any buildup of methane gas from the silo.
The explosion occurred early in the morning on May 1, 1982, devastating the silo roof,
head house, and conveyor handling system. Witnesses stated that a flash was noticed in
the vicinity of the head house, followed seconds later by an explosion that displaced the
silo top structures. This was followed by an orange-colored fireball that rolled down the
silo walls and extinguished prior to reaching the base of the silo. Fortunately, neither injury