The Transportation Safety Board says 13 cars carrying propane and oil on the westbound Canadian National (TSX:CNR) freight train derailed in October 2013 because there were rail breaks along a curve in a siding near the community of Gainford.
One of the derailed propane tank cars was punctured and exploded into a fireball. Two other propane cars also caught fire. The oil tank cars were damaged but did not leak.
The board says the rail in the Gainford siding that failed was old and near the end of its life span. It was inspected two months before the derailment.
The report says railways need to keep the surface of rails clean and smooth or there is a risk that ultrasonic tests won't detect flaws in the metal.
"These defects, they grow over time, and they get to the point where they can no longer support the load and they snap," George Fowler, a civil engineer with the safety board, said Tuesday at a news conference.
"And that is what happened in this particular case. That one defect snapped the rail and the whole derailment resulted in the pileup of the (liquefied petroleum gas) cars and crude oil cars."
Although no one was hurt, more than 120 people were forced to evacuate the hamlet for four days. Almost 200 metres of track was destroyed and a house directly north of the derailment was damaged.
Fowler said there are as many as two dozen problems that rails can suffer, but "transverse defects" such as the ones found at Gainford are the trickiest to deal with.
"They are probably the worst defect because you can't see them with the naked eye and generally you only find them through ultrasonic testing or if they break in service."
CN said it has brought in new safety measures for rail sidings such as Gainford since the derailment. They include walking inspections and retests of all similar sidings across its system.
The company also said it now grinds rails used on sidings to keep them smooth and free of rust. That helps control wear on the metal and ensures that ultrasonic devices used to test rails can detect flaws.
"The industry and all Canadians benefit greatly by the rail industry and the federal regulator working together to fully understand how and why transportation incidents occur," CN spokesman Jim Feeny said in an email.
Rod Shaigec, mayor of Parkland County, has said it was fortunate that no one died. He hopes the report will lead to better safety inspections of rail lines.
Former Gainford resident Jeanette Hall, whose home was most badly damaged, still gets spooked by the sound of a freight train. She said Monday that she would like the Transportation Safety Board report to lead to better rail industry safety.
Last week, the federal government announced it will bolster rail safety inspections, demand higher insurance liability from small carriers and create a disaster relief fund paid for by oil producers.
The measures are in response to a July 2013 explosion and fire in Lac-Megantic, Que., where a crude-laden train derailed, killing 47 people and incinerating the downtown core.
Also on HuffPost