Investigators are trying to determine what caused Saturday night's explosion of a TransCanada Corp. natural gas pipeline in northern Ontario.

James Millar, a spokesman for the Calgary-based company, told NGI that Line 2 -- one of three parallel lines comprising the Canadian Mainline -- ruptured at 11:10 p.m. EST. The incident occurred about two kilometers (1.24 miles) from the town of Beardmore, ON, 170 kilometers (105.6 miles) northeast of Thunder Bay, ON.

"There were some people who voluntarily left their homes, but there was no official evacuation," Millar said, adding that Beardmore has about 345 residents. "They returned to their homes in about an hour. There was no danger to the public [and] nobody was injured."

Millar said workers at the company's gas control center in Calgary detected a drop in pressure and were able to remotely shut down valves on both sides of the rupture -- creating a segment 28 kilometers (17.4 miles) long -- within five minutes. He said the fire at the explosion site burned off residual gas in the segment through the night and finally ended Sunday at about 8:45 a.m.

Officials from the company, the Canadian Transportation Safety Board and the National Energy Board arrived at the site Sunday afternoon and were working to determine the cause of the explosion, Millar said.

"It was pretty difficult [for officials] to get on the scene," Millar said. "It's in a remote area and the only access is by snowmobile or helicopter. We are starting to assess the situation and determine the cause."

Millar said Line 1 is currently operational but Line 3 remains isolated. He said gas shipments would not be disrupted by the incident.

"Line 1 is back in service, so we are able to meet all of our firm contracts with [it]," he said. "We're hoping to have Line 3 operational in a few days. There is no damage to Line 3. It's just a case of insuring that it is fully operational." A company statement added that it was unlikely any discretionary services would be authorized in the impacted area until Line 3 was back in service.

Millar said the Canadian Mainline, which runs about 14,000 kilometers (8,700 miles) from Alberta to Quebec, has a daily capacity of 7 Bcf, but the average amount shipped daily in 2010 was around 3.4 Bcf. He said the section of pipeline that exploded was constructed in 1972, and the three lines in that area run parallel about 35 to 50 feet apart and two feet below ground.

"We're essentially running at reduced capacity," Millar said. "Once [the investigators] release the site to us -- which we're expecting in the next couple of days -- we can immediately begin repairs on Line 2. We're ready to start that once they release the site to us." He said the company was still trying to determine how much the repairs would cost.

Saturday's natural gas pipeline explosion, the fourth since September, could add to growing concerns about the age of the natural gas pipeline infrastructure in the U.S., and help advance pipeline safety legislation through Congress. One bill, S 275, was introduced earlier this month by U.S. Sens. Frank Lautenberg (D-NJ) and Jay Rockefeller (D-VA) (see Daily GPI, Feb. 16).

On Sept. 10 eight people were killed and 35 homes were destroyed in San Bruno, CA after the explosion of a Pacific Gas & Electric pipeline (see Daily GPI, Nov. 2, 2010; Sept. 13, 2010). Five people were killed when an underground gas line owned by utility UGI Corp. exploded in Allentown, PA on Feb. 9 (see Daily GPI, Feb. 14a; Feb. 11). A segment of the 36-inch diameter Tennessee Gas Pipeline, owned and operated by El Paso Corp., exploded on Feb. 10 and caused a fire near Dungannon, OH. There were no injuries (see Daily GPI, Feb. 14b).

©Copyright 2011 Intelligence Press Inc. All rights reserved. The preceding news report may not be republished or redistributed, in whole or in part, in any form, without prior written consent of Intelligence Press, Inc.