An April fire that shot 9-foot flames into the air and shut down the pipeline that moves Alaska's North Slope oil occurred when a worker using a wrench caused a spark near a vent that releases fumes from a large oil tank, an official with Alyeska Pipeline Service Co. said on Monday.
The April 20 fire occurred at Pump Station 5 following preparatory work for a maintenance shutdown of the 800-mile trans-Alaska oil pipeline that was planned two days later, said Michelle Egan, communications manager for the pipeline operator. It led to a nine-hour shutdown of the line.
Alyeska Pipeline released the information on Monday following a preliminary review into the fire. A full report will be completed later.
The pump station is one of a dozen along the pipeline that stretches between Prudhoe Bay and Valdez. But instead of pumping oil, the station serves as a pressure-relief station for oil descending from 4,700-foot Atigun Pass in the Brooks Range, the highest point in the line.
Egan said the pipeline technician was loosening some of the 12 nuts on a metal access plate to the vent. The step has been done in the past to reduce the work associated with an inspection of the vent, with workers removing about eight of 12 nuts without incident, she said. The vent is one of several that rings the top of the 40-foot-high tank capable of holding 150,000 barrels of oil to relieve pressure that can build up in the nearby pipeline.
The worker was using an adjustable wrench, not a power tool, Egan said.
"He was holding it, it slipped and it struck" a metal object, she said.
The accident caused a 3-inch flame to flare from the edges of the access plate. The worker did not have fire-dousing equipment with him atop the tank, Egan said.
"He notified the control room and went down off the tank to retrieve the fire extinguisher, but flames had grown too much so he couldn't go up with a hand-extinguisher and extinguish them," she said.
"Extinguishers are required for what we refer to as 'hot' work --- work such as welding, cutting, grinding and using motorized equipment that could generate heat, flame or spark," Egan said. "This work was not considered 'hot' work, therefore an extinguisher was not required."
The flames, flickering, had jumped up to between 8 and 9 feet high, she said.
The pipeline was shut down minutes after the worker spotted the first flames, with the tank isolated from the pipeline that moves more than 500,000 barrels of oil daily. Workers were evacuated to a safe area, Alyeska Pipeline said previously.
Once the company's full report is completed, it will be reviewed by the federal Pipeline and Hazardous Materials Safety Administration, which regulates the transportation of hazardous materials, Egan said.
Egan has previously said the federal agency has launched its own review of the fire. The agency has not responded to requests for comment about the review.
With the completion of its full report, Alyeska Pipeline will likely recommend changes to its operations to prevent a repeat of the accident, said Egan. Until then, all work on tanks has been suspended unless a director approves it.