An ammonia leak at the Alaska Nitrogen Products (formerly Unocal) plant sent five workers to the hospital Thursday night. None were severely hurt, according to company officials.
At about 8:10 p.m., an electrical glitch caused safety valves to open on two tanks storing anhydrous ammonia.
The incident lasted about 40 minutes, during which personnel evacuated the plant, treated nine people for inhalation of caustic fumes and closed the valves.
"It was an exciting time," said Denise Newbould, the plant's environmental, health and safety supervisor.
The problem is linked to the plant's turnaround, a regularly scheduled maintenance and upgrade period. Half the plant was off-line for the work, which is due to finish Tuesday.
A temporary power source was used in some areas while crews were working on the regular generation system. When workers switched back to the regular power source, the electrical connection to a control computer failed. The controls automatically opened the valves to prevent potentially dangerous pressure build-up in tanks.
Plant specialists were able to restore the power within about 10 minutes, which shut down one leak, and repressurized the valves on the second tank, stopping that leak about 30 to 40 minutes after the initial leak.
About 8,000 pounds of ammonia, a caustic gas, was released altogether.
Weather conditions were calm and rainy, causing the gas to pool near the ground where workers were evacuating. Some reported respiratory distress or skin irritation. Those affected were working for subcontractors involved in the maintenance.
The Nikiski Fire Department responded at 8:48 p.m. with two ambulances and a fire truck. Four people were treated with oxygen on the scene and returned to work. The ambulance crews transported four people to Central Peninsula General Hospital initially and one later.
Four were treated and released; one was held overnight for observation, Newbould said.
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