Before Monday’s fiery derailment of an oil train near Casselton, North Dakota, leading to the evacuation of nearly 3,000 people, the state government was commissioning a study that would show it was safe to move massive amounts of oil on 100-car trains. Once finished, the report would try to dispel the negative press the state’s oil industry was getting since 47 people were killed in Lac-Mégantic.

Now regulators and industry officials are wondering why the oil is exploding.

The Pipeline and Hazardous Materials Safety Administration (PHMSA) issued a safety advisory ”to notify the general public, emergency responders and shippers and carriers 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.”

In addition, PHMSA warned that improper safety measures taken by oil transporters are in urgent need of being addressed. Businessweek reports:

"The agency’s findings may expedite the rail industry’s push for stronger tank cars for moving crude and other hazardous materials. It strengthens calls for the petroleum industry to accurately label tank-car contents and test shipments to make sure they don’t contain gases from the lighter oil produced in the shale rock in North Dakota. “We believe there is sufficient cause for concern,” about whether crude shippers are properly labeling tank cars’ contents, Jeannie Shiffer, a pipeline-regulator spokeswoman, said in an e-mail."

Despite crude being flammable, it's almost never the cause of explosions before being refined into products like gasoline, the Wall Street Journal reports.

But when the BNSF Railway Co. train carrying crude collided with another train, it released a series of explosions on Tuesday.

"Crude oil doesn't explode like that," said Matthew Goitia, chief executive of Peaker Energy Group LLC, a Houston company that is developing crude-by-rail terminals.

Federal investigators, and railroad and energy company officials are investigating whether additives to the crude or incorrect labeling of the liquid contents played a part in the series of explosions.

The Federal Railroad Administration, and Pipeline and Hazardous Materials Safety Administration launched a joint probe called the "Bakken Blitz" before the latest explosion in North Dakota, hoping to uncover what impurities might be in the crude oil.

WSJ:

"Liquid crude oil is extremely difficult to ignite," API spokesman Brian Straessle said, "but the same property that makes it such an excellent source of energy means it is possible that rail accidents caused by human error, track defects, trains running into each other at very high speeds, or other rail issues could cause ignition." The energy industry has been reluctant to discuss publicly what might be causing the problem. It is possible, experts say, that unusually large amounts of naturally occurring and highly flammable petroleum products such as propane and ethane are coming out of the ground with the Bakken crude. Last March, Tesoro Logistics TLLP +1.84% LP reported the Bakken crude it was transporting by rail was increasingly volatile. The San Antonio company didn't respond to a request for comment. Another possibility is that impurities are being introduced during hydraulic fracturing, or fracking. That process involves pumping chemicals or other additives along with water and sand into a well to free more fossil fuels. One such additive is hydrochloric acid, a highly caustic material, which federal investigators suspect could be corroding the inside of rail tank cars, weakening them. Oil from fracked wells can also be laced with benzene and other volatile and highly flammable organic compounds. Enbridge Energy Partners EEP -0.34% LP threatened in May to shut down a North Dakota rail facility operated by the company because there was too much hydrogen sulfide, a potentially deadly and corrosive gas, in the crude being loaded there. The Houston company didn't respond to a request for comment.

Since 2009, the number of carloads transported by U.S. railroads has drastically escalated, from 10,840 to an estimated 400,000 this year.

"It's a grave concern," said Dan Sietsema, the emergency coordinator in northeastern Montana's Roosevelt County, where oil trains pass through the city Wolf Point regularly.

"It has the ability to wipe out a town like Wolf Point."

In a review of federal hazardous material accident records, the AP found they involved small quantities of oil, and railroads say 99.997 percent of hazardous materials that are shipped arrive at destinations safely. Fuzzy math, eh?

However two major reports in July detailed by Desmogblog reveal oil, gas, and coal – the fossil fuel trio -- are inherently unsafe industries regardless of the mode of transport.

Jim Hall, a former NTSB Chairman, said a comprehensive review of national policy on carrying crude was long overdue.

"It appears this is going to be in our nation's communities for the next decade," Hall said. "With this kind of transportation of hazardous material, there are a whole lot of issues that come to mind, not the least of which is terrorism. You are creating a movable bomb from community to community."

The Association of American Railroads in November asked regulators to require most of the U.S. tank car fleet, about 92,000 cars, to be replaced or retrofitted to make the equipment better able to withstand a crash. The Washington-based trade group’s members include BNSF, owned by Warren Buffett’s Berkshire Hathaway Inc.

But switching to sturdier tank cars that would take longer to catch fire -- and include larger pressure-relief valves and other features to cut the risk of a breach -- might cost energy companies $1 billion or more, according to the American Petroleum Institute, which not surprisingly opposes any proposals to upgrade all existing tank cars too quickly.