ANCHORAGE - A massive release of Prudhoe Bay natural gas that filtered into a trans-Alaska pipeline pump station could have destroyed the building and caused an extended shutdown of Alaska's North Slope oil fields, pipeline operators and investigators said.
The incident Jan. 15 occurred as workers for BP PLC, which operates the nation's largest oil field, used pressurized natural gas to move a cleaning pig through a corroded 34-inch pipeline that was being prepared for decommission.
When the pig - a device inserted to scrape walls, detect abnormalities or perform other functions - became stuck, a large volume of gas bypassed it and went to Pump Station 1.
The rush of natural gas overwhelmed systems before escaping out of storage tanks into the atmosphere.
An investigation by federal and state authorities is under way into the incident, a federal regulator said Friday.
Officials at Alyeska Pipeline Service Co., the company that operates the 800-mile pipeline, acknowledge that a fire or explosion could have endangered the station's 60-plus workers and caused a shutdown of oil fields.
The incident occurred as BP workers used the pig to swab oil out of an old 34-inch pipe. The pipe was among major Prudhoe trunk lines found in 2006 to be severely corroded due to BP's lack of proper maintenance.
Pigs typically are shaped like oversized bullets and ringed with discs that scrape the inside wall of a pipe as they slide through. Workers used pressurized natural gas to push the pig.
The pig became stuck and workers "lost track of its exact location" along the pipeline, according to a preliminary report Alyeska prepared for regulators.
A large volume of gas then bypassed the pig and rushed to Pump Station 1, through which all oil coming off the North Slope must pass. The gas caused the station's pumps to "overspeed" and shut down.
Incoming oil and gas was diverted into two huge storage tanks adjacent to the pump station.
Large volumes of gas escaped out relief vents and hatches into the air and some burned in a safety flare near the tanks.
The pump station shut down for more than half an hour, from 3:06 p.m. to 3:41 p.m. Workers were ordered to evacuate some areas.
The potentially catastrophic incident alarmed regulators as well as BP and Alyeska workers. Everyone at the pump station was asked to submit to interviews as part of the investigation.
Federal pipeline regulator Jerry Brossia said the pump station could have burned down.
A spokeswoman for Alyeska on Friday acknowledged the close call.
"It was a very serious event," said Michelle Egan.
Alyeska's report faults BP, a nearly 50 percent owner of Alyeska, for mistakes leading up to the Pump Station 1 incident.
In planning the cleanup of the old pipe, BP did not consider a scenario of the pig getting stuck or stalled, or the "possibility of significant gas breakthrough," according to the report.
Also, BP planners failed to involve Alyeska workers who understand the pump station's equipment and operation.
The incident shows that oil producers need to work more closely with the trans-Alaska pipeline operator, Brossia said.
BP spokesman Steve Rinehart acknowledged planning lapses. Although BP did a safety analysis, the analysis was "flawed" and no burst of natural gas was supposed to reach Pump Station 1, he said.
BP also needs to tighten its work with the pipeline operator, Rinehart said.
"We're going to use this incident to improve our practices and our procedures and to enhance our communications with Alyeska," he said.