Oil flowing through the trans-Alaska pipeline returned to normal levels Thursday morning after a fire at a pump station that led to an unusual nine-hour shutdown of the line and a restart that began with reduced flow.
Two investigations also got underway to determine the cause of the fire in a pressure vacuum vent that allows crude oil vapors to escape from a large oil tank at the pump station near Coldfoot south of the Brooks Range.
Alyeska Pipeline Service Co., which operates the 800-mile pipeline on behalf of its major owners, BP, ConocoPhillips and ExxonMobil, is conducting an internal investigation into the cause of the fire, said Michelle Egan, communications manager for Alyeska.
"It's part of our normal practice to determine the root cause of an event and then apply those lessons going forward," Egan said.
Also investigating is the federal Pipeline and Hazardous Materials Safety Administration, which regulates the transportation of hazardous materials. PHMSA is among the agencies that have sent personnel to the site at Pump Station 5, off the Dalton Highway.
The pipeline moves the North Slope crude oil that's long been critical to the state's economy. Oil flow was restarted about 11:30 p.m. Wednesday at a rate of about 400,000 barrels per day.
At 8:45 a.m., Alyeska asked oil producers to return to full volume production from 75 percent," said Egan, allowing "full flow" to resume. Full flow lately has been about 540,000 barrels of oil daily.
The pump station is one of a dozen along the line that stretches between Prudhoe Bay and Valdez. But oil isn't actually pumped there. Instead, Pump Station 5 serves as a relief station for pressure that can build up in the line, as oil descends from 4,700-foot Atigun Pass in the Brooks Range, the highest point in the line.
The relief tank, shaped like a giant pill at 40 feet high and 170 feet across, can hold 150,000 barrels of crude to help reduce pressure building up in the pipeline.
The Alaska Department of Environmental Conservation was monitoring the situation with personnel on site, said spokesperson Candice Bressler.
"At this time we know there hasn't been a release," she said Thursday morning.
Bressler said DEC staff will coordinate with Alyeska to review tank inspection records and make sure the tank is fit for service.
Technicians at the Alyeska control center in Anchorage shut down the pipeline minutes after an Alyeska worker spotted flames shooting from the vent at about 2:30 p.m. Wednesday.
Fifty-eight workers were moved to a safe area and the pipeline was safely isolated from the tank, Egan said. There were no injuries.
A fire crew providing contractual services for Alyeska -- Houston Contracting Co., owned by ASRC Energy Services -- put out the fire at about 1 a.m. Thursday, using a hose to direct fire-suppression chemicals at the vent, Egan said.
The fire was confirmed to be extinguished about 8:30 a.m. Thursday, said Bressler. Alyeska used an infrared camera that detects radiation from heat – a forward-looking infrared camera -- to confirm the fire was out.
Egan said she did not know how long the investigation might take.
"We're pretty thorough, so it can take a while," she said.
The pipeline is shut down several times a year for maintenance, including for longer durations in summer that may last 36 hours. But shutdowns related to unexpected problems like the fire are rare, said Egan.