As the sun began to rise, the cloud became more visible and its
extent could be estimated. Several square miles were blanketed with a
greenish haze, sitting just above ground level. It became obvious that the
leak was not controlled and that direct action would be needed to stop the
flow. It was not known how much liquid had leaked out, but the amount
that could potentially escape was now estimated at 100 tons or more.
Consultation with plant personnel led to the conclusion that the leak could
only be stopped by placing a blank flange in the line between the storage
tank and the leaking elbow. An entry team was assembled, including both
Fire Department and plant emergency personnel, to go in and insert the
blank flange.
Note: A blank flange is a solid plate, cut to the appropriate size to fit
between the two pieces of a flange pipe connection. To insert the
blank flange, the bolts must be removed from the existing flanged
connection and the plate inserted between the two halves. The bolts
are then reinstalled and tightened.
The entry team dressed in Level B protective clothing and selfcontained
breathing apparatus approached the area of the leak. They
found that the hole in the pipe had expanded to approximately one-inch
diameter and was producing a steady stream of liquid chlorine. The liquid
had formed a pool from which the chlorine was vaporizing rapidly.
To install the blank flange it was necessary to work within two feet
of the actual leak, under the spray of the leaking liquid. Plant employees
performed the actual installation of the blank flange, backed-up by Fire
Department members. The first attempt, at approximately 0630 hours,
proved unsuccessful when the highly corrosive liquid damaged the steel
plate before the bolts could be tightened. A second attempt was
successful, at another flange location, using a Teflon-coated steel plate.
The leak was stopped by approximately 0730 hours.
With the leak stopped, the problem began to diminish. The
remaining liquid on the ground vaporized quickly and the vapor cloud
began to dissipate under improving weather conditions. Over the next
three hours the heat of the sun warmed the ground and provided buoyancy
for the cloud, while a more normal wind condition helped to move it away
from the populated area. By 1000 hours the cloud had dispersed
completely and evacuees were allowed to return to their homes and
businesses.
For the next 24 hours there was a continuing concern that more of
the stored chlorine might have been contaminated with water and the
corrosive mixture could be eating its way out of additional tanks and
piping. The Clark County Fire Department HazMat Team continued to
stand by until sampling of the remaining storage concluded that the
contaminated chlorine was contained in one storage tank and most of its
contents had leaked out. Preparations were made to disassemble the heat
exchanger where the problem was believed to have originated.
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