Train derailments provide ideal conditions for an oil explosion, say chemists and engineers from across North America, calling into question rail’s ability to transport hydrocarbons safely and to prevent catastrophe in the event of an accident.

While the massive explosions that killed 47 and leveled Lac-Megantic, Que. in 2013 were fuelled by particularly volatile “light” crude oil from the Bakken region of North Dakota, two derailments in the last month in Gogoma, Ont., both involved “heavy” crude from Alberta’s tarsands, and exploded just the same.

“If all conditions are equal, both light and heavy hydrocarbons will ultimately explode,” said Raj Mehta, a professor of oil and gas engineering at the University of Calgary. “But one will take a little longer.”

Heavy crude is often considered difficult to ignite because it will only burn when exposed to a flame, and will stop burning when the flame is removed, said Mehta, an expert in combustion. But train derailments involve so much heat and pressure, heavy crude will not only ignite, it can explode.

When a train carrying tanker cars full of crude oil derails, the three ingredients necessary for an explosion are all present, said Mehta. Heat is produced by the brakes and the impact between cars. Combustible fuel is created when that heat starts to vaporize the oil in the cars. And oxygen is accessible as soon as the smallest crack or rupture in the tanks appears and the oil sprays out.

“All the hydrocarbons will burn, provided you have the right mixture of air and hydrocarbon,” Mehta said.

In Gogoma, some residents thought there had been an earthquake, said France Gelinas, MPP for the Nickel Belt, who visited shortly after the crash. She was shown photos of a fire ball 100m high that exploded just after the train passed through town.

“I don’t scare easily, but that was scary,” she said. “Everyone was talking about Lac-Megantic.”

After the Lac-Megantic disaster, both the U.S. and Canadian governments identified shale oil from the Bakken region as a particularly hazardous for rail transport.

Bakken crude, which is already lighter and more likely to vaporize than the “light, sweet crude” from West Texas, Saudi Arabia or Venezuela, often has a high amount of other even more volatile components present, including hydrogen sulphide, said Ramanan Krishnamoorti, a professor of chemical and biomolecular engineering at the University of Houston. These components are stripped out of the oil before transport.

On the other end of the spectrum, heavy crude from the Alberta oilsands, is the “least volatile” kind of crude, Krishnamoorti said.

“Shipping bitumen is relatively easy. You don’t necessarily worry so much about it volatilizing and becoming a combustible fuel rapidly,” he said.

But because bitumen is so thick, chemicals are often added to get it into tanker cars. These additives are themselves highly flammable rendering the otherwise low-risk bitumen much more explosive, he said.

These different components can settle out inside a tanker, leaving highly volatile dilutant at the top, ready to vaporize and explode, said Mark Winfield, an associate professor of environmental studies at York University who studies public safety regulation.

“There’s always a risk of ignition,” he said. “The physics of the thing is that you’ve got a combustible liquid and a lot of energy in a moving train.”

Following Lac-Megantic, Transport Canada announced that it will be studying the makeup of crude oil being transported with a view to better understanding and classifying the volatility of the oil being transported by train.

“Maybe they should have done that in 2011, when oil by rail started taking off,” said Winfield. “It’s a bit late now.”

Millions of litres of crude from both the U.S. and Alberta are now transported by rail across the country, passing through the centre of small towns like Lac-Megantic and Gogoma as well as the downtown core of Toronto.

This rapid increase in the use of rail has overwhelmed both physical infrastructure and regulations, Winfield says, and accidents have been the result.

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While much of the government reaction has focused on improving the tanker cars, which would take years to reach the rails, a much simpler solution could be introduced immediately, said Winfield.

“The better strategy is ultimately to slow down,” he said. “Energy is a component of speed.”

“I don’t know what speed the train was going in Gogoma, but after seeing the photos of all those cars piled up, I imagine it must have been going pretty fast.”

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