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OTTAWA (Reuters) - The fiery January 2014 derailment of a Canadian National Railway Co crude oil train in New Brunswick was caused by an undetected flaw that broke a wheel, the Transportation Safety Board of Canada said on Friday.
The accident at Plaster Rock in the Canadian Atlantic province was one of a series of tanker train disasters that have increased concerns about the safety of shipping crude oil by rail in North America.
After the wheel broke, 19 cars derailed, spilling 61,000 U.S. gallons (230,000 liters) of crude oil that caught fire. About 150 residents were evacuated within an one-mile (1.6 kilometer) radius of the fire, but no one was injured.
"A wheel on the 13th car shattered due to an area of subsurface porosity (a cavity) that led to fatigue cracking," the TSB said in a official report.
"The subsurface porosity was not detected during the ultrasonic testing when the wheel was manufactured in 1991, or when it was reprofiled in 2006," the report added.
A spokesman for CN Rail, asked whether the company was concerned that the defect had not been caught, said CN had not manufactured or reprofiled the wheel that broke.
Last year the TSB said a broken wheel had caused the derailment of a Canadian Pacific Railway Ltd crude oil train in Ontario in April 2013.
Broken wheels cause around three derailments a year in Canada, the TSB said.
"Although the number of derailments is fairly low, they can pose serious risks because these types of derailments occur at high speeds," it said.
Reporting by David Ljunggren; Editing by Peter Galloway