[Circumstances of Incident]
An explosion
occurred inside a tank during repair work on wastewater treatment
facilities located within the premises of an oil refinery.
The
wastewater treatment facilities are comprised of oil/water separation
equipment, dissolved gas removal equipment, activated carbon adsorption
equipment and other equipment in order to remove environmental pollutants
from the wastewater discharged from each process of the plant. The
wastewater tank is provided for holding operations in order to keep the
treatment volume constant.
During normal operations, the upper 60
percent of this wastewater tank contains gas while wastewater after oil
separation and accumulated sludge make up the remaining portion. Most of
the gas is hydrogen sulfide, although some nitrogen, ammonia, hexane,
etc., are also included.
The purpose of repair work was to clean
the 250m3 wastewater tank and coat the interior walls of the
tank.
On the day of the accident, preparatory work for the repair
work began at 9:00 in the morning. In order to first confirm the situation
of the remaining wastewater within the tank, the cover of the manhole was
raised 15cm by a chain block, and the sludge situation was checked. When
the cover of the manhole was put back in place, flames and white smoke
erupted from the manhole with a muffled thud. As a result, five workers
suffered from burns.
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