09/11/2013 09:59 EDT | Updated 11/11/2013 05:12 EST

Lac-Mégantic disaster oil more dangerous than stated

The crude oil carried in tankers that derailed and ignited in Lac-Mégantic, Que., in July was misclassified as a less volatile substance, the Transportation Safety Board of Canada announced this morning.

At a news conference in Ottawa, the lead investigator on the rail disaster, Donald Ross, said that misclassification, "explains in part why the crude ignited so quickly once the train cars were breached."

The revelation comes after tests were conducted on oil contained in nine train cars belonging to Montreal, Maine & Atlantic railway that were not involved in the explosion.

The 72-car, unmanned train rolled down an incline into the core of the town, left the tracks and exploded early in the morning on July 6. The blast and fires killed 47 people and destroyed several blocks neighbouring the train tracks.

The TSB said it was immediately issuing safety advisory letters to rail authorities in Canada and the U.S., where the train originated, to review the processes for suppliers and companies transporting dangerous goods to ensure the description of the products are accurate and documented properly.

The crude oil in the Montreal, Maine & Atlantic train that derailed in Quebec had been listed as packing group three, the least hazardous on the scale.

The oil actually had the properties of a class two substance, which also includes goods like gasoline, that have a lower flash point and will therefore ignite quicker.

It's the responsibility of the importer, in this case New Brunswick-based Irving Oil, to ensure the description of the products are correct, Ross said.

Ross said the response by firefighters would not have been affected by the packing group and the tankers used to ship the crude wouldn't have necessarily have been changed if the oil had been correctly identified.

"It’s a possibility that it had no effect, but we’re not saying that yet," he said.

The TSB investigation is ongoing and remains a top priority, Ross said.