A storage tank containing 93 percent sulfuric acid
ruptured and its contents were released to the environment. Employees
responded to the acid spill by constructing a dike, using gravel, lime
and sand. Forklift drivers removed galvanized poles from the spill. The
acid reacted with the lime, and released a white "cloud" with irritating
properties which enveloped many of the responding employees. The
employer called the Fire Department HAZMAT Team who responded
to the scene. When the HAZMAT Team arrived employees were ordered to
cease activities. This facility used sulfuric acid in the galvanizing
process. The horizontal tank that ruptured had a storage capacity of
3,770 gallons of sulfuric acid and was located outside the facility in
containment. It was used to replenish the sulfuric acid dip tanks. It
was not designed and manufactured as a pressure vessel. The tank
ruptured during the transfer of acid from the storage tank to dip
tank(s) located inside the plant. Acid was transferred from the storage
tank to dip tank(s) by pressurizing the storage tank with compressed
plant air. The compressed plant air line went through an in-line air
dryer which had not been maintained according to the manufacturer's
instructions. The compressed air pressure to the storage tank was
normally reduced from 120 psig by a regulator down to 30 psig. However,
engineering design criteria specified that the regulator be set at 10-15
psig. After the accident, the regulator was found to be set at 90 psig.
In addition, the regulator had recently been replaced and did not meet
the engineering design specifications of the original regulator. An
accident investigation concluded that the tank ruptured due to
over-pressurization within the tank. After their exposure, employees
reported burning faces, throats, headaches, and chest pain. Many of the
employees coughed and choked, and had difficulty in breathing.
Source:osha.gov