March 6 (Bloomberg) -- BP Plc, the second-largest oil producer in Alaska, risked causing an explosion when it cleaned an oil pipeline in the state in January, according to a report on the incident by Alyeska Pipeline Service Co.

BP caused a 34-minute shutdown of the nation’s largest oil pipeline, the Trans-Alaska Pipeline, an 800-mile (1,287- kilometer) conduit that carries about 700,000 barrels of oil a day, Alyeska said.

A fire or explosion could have injured some of the 63 workers at the site and disabled an adjoining pump station, resulting in a longer shutdown of the pipeline, according to the report by Alyeska, the group of oil companies that runs the pipeline, including BP, Exxon Mobil Corp. and ConocoPhillips, Alaska’s biggest oil producer.

“We recognize that the incident was potentially hazardous,” Steve Rinehart, a BP spokesman in Anchorage, said in an interview. “The conclusion is that the safety-process analysis was inadequate.”

In the Jan. 15 incident on Alaska’s North Slope, BP workers used a bullet-shaped maintenance device called a “pig” to remove oil from a smaller pipeline being decommissioned that feeds into the Trans-Alaska pipeline.

‘Significant Risk’

Workers injected natural gas to push the device through the pipeline. It got stuck, and workers lost track of its location, Alyeska said in its report. BP did not properly evaluate what could happen if the gas bypassed the device, the report said.

The gas flowed past the pig and went into a pump station at the much larger Trans-Alaska Pipeline, which isn’t built to move gas, the report said. That caused pumps to over-spin, sending gas into oil-storage tanks, where some was vented into the air, posing a fire hazard, according to the Feb. 23 report.

The incident posed a “significant risk to personnel and equipment” including a fire or explosion, according to the report.

In a separate report dated Feb. 25, BP confirmed Alyeska’s conclusions and acknowledged that it didn’t properly evaluate the risks of the cleaning procedure.

The reports from Alyeska and BP were submitted to the Joint Pipeline Office, a group of state and federal agencies that regulates the Trans-Alaska Pipeline. The office released the reports to Bloomberg News.

“It’s pretty fortunate that the gas was not near any ignition source,” Mark Morones, a spokesman for the Joint Pipeline Office, said in a telephone interview.

State and federal agencies have been given copies of the reports and will be reviewing BP and Alyeska’s findings, Morones said.

The U.S. Department of Transportation’s Pipeline and Hazardous Materials Safety Administration is investigating the incident, Patricia Klinger, an agency spokeswoman, said in a telephone interview. The agency, which oversees compliance with oil pipeline regulations, will determine if there were any violations, she said.

Last month, BP agreed to spend almost $180 million to resolve allegations that it violated clean-air regulations at its oil refinery in Texas City, Texas, where an explosion in March 2005 killed 15 workers and injured more than 170.

One of the feeder pipelines in Alaska’s Prudhoe Bay oil field, operated by BP, corroded and ruptured in August 2006, partially closing the biggest oilfield in the U.S. for about three months. BP agreed to replace 16 miles of corroded pipelines.

To contact the reporter on this story: Tony Hopfinger in Anchorage at thopfinger@gci.net.

Last Updated: March 6, 2009 17:38 EST