Narrator: The Bayer CropScience plant is a
large chemical complex of more than 400 acres on the Kanawha River near Charleston. It is located in a populated area
next to West Virginia State University. Bayer operated four manufacturing units, using highly
toxic chemicals, including methyl isocyanate or MIC, to produce carbamate pesticides
and other products. One unit, located adjacent to a 6,700
gallon capacity storage tank of MIC, used a series of chemical reactions to
synthesize the Bayer pesticides, Methomyl and Larvin. During the summer of 2008, the Methomyl-Larvin Unit was
shut down for several months of scheduled maintenance, a major control system upgrade and replacement of a 25
year old pressure vessel called the "Residue Treater". Inside this vessel, residual Methomyl
was decomposed at a high temperature, so the waste solvent could be
used as fuel elsewhere in the plant. This process released heat and needed to be
carefully controlled to prevent a runaway reaction. Bayer was eager to get the unit back online
to meet increased demand for Larvin, with workers putting in
extended hours to get the job done. A decision was made to restart the unit,
but this was premature; workers faced numerous equipment problems
and the new computer control system had not been fully calibrated
and was not ready for use. This made the
startup particularly risky. Five days into the startup of the unit,
the Residue Treater was brought online. For safety reasons, the vessel needed to
be prefilled with clean solvent and heated, to prevent a dangerous accumulation
of reactive Methomyl during startup. A safety interlock would prevent Methomyl residue from
being fed to the vessel if the temperature was too low. But some operators believed the heater could not
reach the required temperature to open the valve. Contrary to operating procedure
and with managers' knowledge, operators used a password to
bypass the safety interlock. This routine work-around increased
the likelihood of a runaway reaction. Other equipment problems diverted the
operators' attention and on the day of the accident, they mistakenly did not
prefill the vessel with solvent. Adding to the dangers, problems with a crystallizer
raised the concentrations of Methomyl in the residue significantly above
the safe operating limit. During the day, the over-concentrated Methomyl
inside the vessel began to decompose, releasing heat. As the temperature climbed, the rate
of the decomposition reaction increased rapidly. By 10:00 p.m., the temperature
was approaching the safety limit. At 10:17, the pressure began to climb quickly,
unnoticed by the board operator, who was dealing with
other equipment problems. At 10:25, the Residue Treater
high pressure alarm went off. The board operator mistakenly
believed pressure was increasing, because the vent pipe had become blocked,
as had occurred many times in the past. He radioed two outside operators to check the vent pipe
and set the vessel cooling system to "full", but the runaway reaction
could not be controlled. At 10:33 p.m., the Residue Treater
violently ruptured [sound of explosion]. The vessel careened into the production unit,
ripping out piping, the electrical conduit and
a large structural column. More than 2,200 gallons of flammable and
toxic materials sprayed in all directions. A massive fire erupted. Other debris struck the protective steel mesh
surrounding the storage tank, which contained 13,700 pounds
of methyl isocyanate. The two workers, who had been checking the
vessel's vent pipe, were fatally injured. Two other workers and six volunteer firefighters
were treated for possible toxic chemical exposure.
