An ammonia leak at the Alaska Nitrogen Products (formerly Unocal) plant sent five workers to the hospital Thursday night. None were severely hurt, and no dangerous chemicals traveled outside the plant boundaries, 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 workers 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 was 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.
"We had a problem we didn't identify until switching it over," Newbould explained.
Without power, the controls automatically opened the valves.
Mike Nugent, vice president and general manager of ANP, explained that the valves "fail open" as a safety precaution. In case of problems, the system vents ammonia into the atmosphere to prevent pressure build-up in tanks that potentially could lead to major ruptures.
"You don't want to create another situation," he said. "Everything did exactly what it was supposed to do."
Alarms sounded, and workers evacuated.
Weather conditions were calm and rainy, causing the gas to pool near the ground where workers were passing. Because of poor visibility, some ran into or through clouds of ammonia and reported respiratory distress or skin irritation, Newbould said.
The affected workers were employees of subcontractors involved in the turnaround maintenance. She identified the companies as Koch, CustoFab and Peak Oilfield Services.
"When we have contractors on site, we do quite a bit of training for events like this. We do safety audits every day during the turnaround," she said.
"Those things pay off. They truly knew what to do."
Despite what she described as a "secondary problem" with the public address system, the evacuation of workers was efficient and took only a few minutes, she said.
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 in Soldotna initially and one later.
Trooper Dennis Chan said injuries included second- and third-degree burns from caustic fumes coming into contact with perspiration.
At the hospital, four were treated, released and returned to complete their shifts. A fifth individual was held overnight for observation, released the following day and returned to work that evening.
Plant specialists were able to restore the power within about 10 minutes, which shut down one leak, and to repressurize the valves on the second tank, stopping that leak about 40 minutes after the venting began.
About 8,000 pounds of ammonia, a caustic gas, was released altogether, she said. The vented gas dissipated in the air and dissolved in the rain. Testing on the highway adjacent to the plant found only traces of ammonia smell.
The community alert system was not activated, but a message about the event was placed on the information recording Nikiski industrial plants operate for the public at 776-3225.
Newbould and Nugent estimated that about 35,000 tons of ammonia were in the two storage tanks, which have a combined capacity of 80,000 tons.
Friday morning the company began investigating the incident. It will convene an internal task force to perform a formal, methodical study. The managers and shop stewards had training this summer in the latest investigative techniques, Nugent said.
ANP is considering routing the storage tank pressure relief valve to the plant flare rather than the atmosphere, according to a situation report issued Friday afternoon by the Alaska Department of Environmental Conservation.
"It's going to take some time to put a long-term fix in place," said Newbould on Saturday. "Our priority task yesterday was to come up with an interim plan to make sure we didn't have an ammonia release from those valves. So we spent the day working on that yesterday, did a hazard analysis on the plan we formulated and finished that about 9 p.m. Today workers did the work to put that plan in place. We're not going to have a release like we had."
Newbould said the incident caused a half-shift delay. Whether the incident and subsequent investigation will delay the scheduled completion of the turnaround remains to be seen.
Despite losing half of a shift's work and one day's production on the half of the plant that remains open throughout the turnaround, the major maintenance project is still expected to wrap up Tuesday. But staff will be setting aside previous tasks to focus on preventing such incidents in the future, Nugent said.
"The investigation and what we decide to do takes priority over turnaround," he said.
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