A Special Agent from the Office of the Illinois State Fire Marshal was the lead
investigator. He was assisted by members of the Illinois State Police; Hancock County
Sheriff’s Office, Hancock County Coroner, Illinois Fire Service Institute, and an independent
engineering consultant. In addition to these agencies, various private cause and origin
investigators and experts were permitted access to the site and equipment under supervision
of the lead investigator. The objective was to identify the cause of the fire and to determine
why the tank BLEVE’d.
Scene documentation began that evening and continued into the next two days.
Photographs and videotape were taken at ground level and from a state helicopter. The
aerial views provided an excellent means to describe the path that the east tank traveled.
The two LP-Gas tanks, parts of the LP-Gas hose fittings that were not consumed
in the fire, and the two pieces of the domed tank head were transported to a secure
location. The portable dryer and the LP-Gas fueled tractor, which powered the dryer,
remained at the site. The extent of damage and size made their movement impractical.
The east LP-Gas tank was moved from the field where it came to rest with a
tank carrier. The north head separated from the rest of the tank at the weld seam.
The metal at the separation seam (fracture surface) was very smooth on both the tank
and on the pieces of the head. The surface was almost like a grinder had passed over
it. There were no chevrons1 on either the tank or the head’s fracture surfaces. The
paint on the south end of the tank appeared blistered while the paint at the north end
was unmarked.
At the time of the scene visit, the roll forming of the metal for the domed head
to the tank cylinder weld seam was being reviewed for proper shape. In addition, the
position and penetration of the weld bead at this seam was being analyzed. Both were
possible contributing causes for the tank failure.
The inside of the tank was clean with no visible corrosion or pitting. The liquid
LP-Gas pickup tube had detached from the liquid withdrawal connection and was
found near the tank’s final resting-place. The tank did receive several dents and
scrapes caused by the tank striking the ground and other objects. In addition, the tank’s
south domed head had a hole about 1/2-inch in diameter punched through the metal.
Marks inside the hole suggested that it had been threaded. A steel rod, threaded on one
end, was found at the third or fourth tank shell impact with the ground. The rod
matched the hole in the head and was traced to the metal pipe rack that the tank struck
in the pole shed. The threaded rod was a support piece for the pipe rack.
The west LP-Gas tank was also moved with a tank carrier to a secure storage
location. At the time of the site visit, the original position and direction that the tank
was facing prior to the incident had not been determined. It is hoped that the hinge
connection for attachment of the protective valve cover may be used to determine
which end of the tank faced north. (See Appendix F for photograph of the tank.)
Around the hinge connection, a two to three inch high blister in the tank shell had
formed over an area about 2 feet long by 1 1/2 feet wide roughly on top of the tank.
The typical cause of tank metal deforming in this fashion is the direct flame impingement
from burning LP-Gas on the tank shell in the vapor space. Allowed to continue,
it is likely that this tank would have also BLEVE’d from the stretched and weakened
metal.
The Office of the Illinois State Fire Marshal contracted with an independent
engineering consultant to assist with the identification of the cause of the original fire.
The consultant’s report described two possible ignition sequences:
Sequence 1: The noise from the dryer was caused by the failure of drive belts to
the blower. The loss of the fan function allowed the dryer burners to flash out
and consume the liquid propane lines and ignite the released propane vapors.
The heat from the propane fire exposed the two 1,000 gallon LP-Gas tanks with
the closer tank receiving the most heat. The heat increased the vapor level,
which forced liquid propane into the other tank.
Sequence 2: Failure of the flexible LP-Gas hose lines in the area of the tractor
and dryer caused a flame roll-out from the dryer. The release of propane from the
hose line resulted in the exposure of the two 1,000 gallon tanks to excessive heat.
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