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OCR for page 13
1
Chapter 3
SUMMARY OF ON-SITE INVESTIGATIONS
In the Appendix detailed information is given on six explosion
investigations conducted by members of the investigation subpanel. It is
useful to point out how the previously discussed methodology was used in
these investigations. Recapitulating, the major steps of the investigation
methodology include physical site examination of pieces and parts of the
elevator complex; determination from rubble, wreckage, etc. of the direction
and origination of blast and combustion waves; and interrogation of
witnesses. In the six incidents described, all of these steps were taken.
In all cases the interviewing of witnesses played an important role in
_ _ _ _ _ _ ~ _ _ ~ _ , _ _ _,
determining the probable scenario. On-gite Investigation was important in
all except the second incident in which the cause was immediately obvious
upon interviewing. In the incidents 1, 3, 4, and 5 the direction of blast
and combustion waves also played an important role in determining probable
sequence of events.
In the f irst incident, considerable site investigation and interviewing
were necessary before the investigators were led to the conclusion that the
ignition resulted from an electrical equipment failure in one of the bins.
Although the precise cause of the initial propagation of the explosion is
not fully deducible, the-end result follows the assumption of a primary
explosion in a loading bin connected directly to other portions of the
facility.
In the second incident, the major explosion was definitely attributable
to the use of firefighting procedures that stirred up dust and generated an
explosive atmosphere. The initial fire was probably caused by a hot light
fixture. -
In the third incident, a light fixture also was the probable initial
cause of a fire in the top of the headhouse cupola structure. The explosion
that occurred after firefighters had arrived at the scene was inevitable
because of the state of housekeeping of the building.
The second and third incidents were fairly easily identifiable events.
However, in the fourth incident, considerable interviewing was necessary
ascertain the events that led to the explosion. The primary cause was a
failing belt; however, only after detailed investigation was the whole story
obtained. The single bucket elevator in the complex had been damaged so
that choking and stoppage had occurred. There may have been a loose bucket
13
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1
l
14 ,
on the belt. Jogging procedures apparently caused a friction fire that
burned through the belt. The main explosion occurred in an inaccessible
concrete legwell through which the bucket elevator passed. The explosion
f orce propagated upward into the headhouse and downward into the tunnel.
Because the concrete legwell shattered early in the explosion sequence, very
little pressure was transmitted to the bulk of the elevator itself. The top
of the headhouse.was damaged because it did not have enough vent area to.
relieve the explosion pressures developed from the legwel1 directly below
the headhouse. However, little damage~was done in the tunnel an the
explosion force had diminished.because of rupture of the main headhouse
walls. In this investigation an apparent discrepancy in the events just
prior to the explosion was later explained when a hospitalized witness gave
a different version of what-had happened and refuted earlier testimony. .
This illustrates the importance of persistence in interviewing to validate
the most probable scenario if it cannot otherwise be verified.
. .
In the fifth incident, site investigation soon revealed that the initial
explosion probably occurred in the headhouse itself or was communicated into
the headhouse from the legwell. The initial explosion occurred someplace in
the bucket elevator casing and propagated into the headhouse proper. The
head Dullev Showed signs of scorching and evidence that the h-1 t had The
_ _ _ ~ _ ~ ~ ~ — 0
· ~ ~ ~ _a ~ _ .
On fire and.broken. This was not confirmed until the wreckage was removed
from the boot area several weeks afterwards. In this instance the
communication from the headhouse to different bins through open spouting led
to additional damage. However, the direction of propagation from leg to
headhouse to other parts of the structure became fairly obvious early in the
investigation. The ruptured bucket elevator confirmed the logical ignition
source.
_ . ~
In the last event, witnesses confirmed that a belt had broken. The site
investigation simply confirmed the expected propagation of blast and
combustion wave damage.after the leg and casing exploded on the bucket
elevator. .
In summary, the logical methodology described for the investigation of
grain elevator explosions can be successful. Observations at the sites and
interviews with witnesses are the principal mechanisms to determine cause.
No investigation can be considered complete until all of the facts coincide
and essentially verify the sequence scenario. Major inconsistencies must be
resolved? or the cause will fall: into the unknown (unverifiable) category.
1
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1
15
REFERENCES
l
1
Brasie, W. C., Guidelines for Estimating the Damage from Grain Dust
Explosions, Proceedings of the International Symposium on Grain Dust,
Kansas State University, Manhattan, Kansas, October 2-4, 19 7 9.
National Fire Protection Association, Explosion Venting, Bulletin No. 68,
Boston, 1978.
National Materials Advisory Board, The Investigation of Grain Elevator
Explosions, NMAB Report 367-1, National Academy Press, Washington, D.C.,
1980.
National Materials Advisory Board, Prevention of Grain Elevator and Mill
Explosions, NMAB Report 367-2, National Academy Press, Washington, D.C.
1982a .
National Materials Advisory Board, Pneumatic Dust Control in Grain
Elevators: Guidelines for Design Operation and Maintenance, NMAB Report
367-3, National Academy Press, Washington, D.C., 1982b.
Verkade, M., and Chiotti, P., Literature Survey of Dust Explosions in
Grain Handling Facilities: Causes and Prevention. Report IS-EMRRI-2,
Energy and Mineral Research Institute, Ames, Iowa, 1976.
OCR for page 16
Representative terms from entire chapter:
grain dust
