The trans-Alaska pipeline will remain shut down overnight as the line’s operating company decides how to clean up oil that overflowed from a tank into a diked containment area at Pump Station 9 just after noon Tuesday.

As much as several thousand barrels of oil overflowed from the 55,000-barrel crude oil storage tank, according to Michelle Egan, Alyeska Pipeline Service Co.’s communications director in Anchorage. No oil escaped the lined area around the tank, which can hold 104,500 barrels, she said.

Pump Station 9 sits a few hundred feet east of the Richardson Highway, eight miles south of Delta Junction and about 110 miles southeast of Fairbanks.

Alyeska began a brief planned shutdown of the pipeline at 9 a.m. Tuesday. During the shutdown, while workers were testing the pump station’s fire suppression system, the power went out, Egan said.

“That loss of power resulted in some valves being opened, which is by design so you don’t over-pressure the system,” she said.

An incident summary released by the state Department of Environmental Conservation at 3:30 p.m. Tuesday stated that the problem occurred when power at the station “was switched from grid to an uninterrupted power source battery.” The battery’s control circuit “failed to control a valve,” according to the summary.

The open valve allowed oil to fill and then overflow the pump station’s crude oil relief tank. The valve was open for about an hour, Egan said.

There were no injuries.

The site has been evacuated while Alyeska analyzes the situation, Egan said. Crude oil can produce strong flammable vapors.