A top transportation safety regulator warned on Thursday that the type of crude oil that exploded rail cars in Lac-Mégantic, Que., last year is more flammable that other forms of oil and needs more careful treatment.

The Pipeline and Hazardous Materials Safety Administration, a division of the U.S. Department of Transportation, warned Thursday in a safety alert that "recent derailments and resulting fires indicate that the type of crude oil being transported from the Bakken region may be more flammable than traditional heavy crude oil."

Bakken oil hails from the Bakken region of the U.S. midwest, just south of Manitoba and Saskatchewan. New technology has allowed for the extraction of so much previously unrecoverable oil that America is now on the road toward energy self-sufficiency within the next decade.

But that new oil has different chemical properties that make it more dangerous to handle, the PHMSA said. Its flashpoint (the point at which the chemical can vaporize and possibly ignite in the air) is as low as 23 C.

"This means the materials pose significant fire risk if released from the package in an accident," the safety warning said.

Bakken oil boom

The Lac-Mégantic​, Que., explosions devastated the town and killed 47 people in one of Canada's worst rail disasters.

This past weekend, a BNSF Railway Co. train carrying Bakken oil caught fire after a collision in Casselton, N.D.

Another oil train derailed and exploded in Alabama in November, killing no one but releasing an estimated 749,000 gallons of oil from 26 tanker cars.

Amid multiple protests against various oil pipelines proposed to soon cut across the continent, the rail industry has pitched itself as a safe, less disruptive alternative to transport oil from oil fields to refiners and the export market.

Lobby groups for the rail industry in the U.S. and Canada are pushing to have rail cars upgraded and retrofitted to handle more and more volumes of oil as the amount of oil moved by rail has spiked since 2009, from just more than 10,000 tanker cars to a projected 400,000 cars in 2013.

Thursday's safety alert resulted in part from results of preliminary tests on Bakken oil to determine just how dangerous it is, said Jeannie Shiffer with the Department of Transportation's Pipeline and Hazardous Material Safety Administration.

Shiffer said it is important to know the volatility of the oil so that it can be properly handled during shipping.

"The material must be properly classified at the beginning of the process. That determines everything," she said.

Last September, Canada's Transportation Safety Board found that the oil that exploded in Lac-Mégantic has been improperly labelled as a less-volatile substance and as such may not have been handled with as much scrutiny.

With files from The Associated Press