(Reuters) - Crude oil produced in North Dakota may be more flammable and prone to explosions than earlier thought, U.S. officials said on Thursday as they examine whether gas trapped in crude-by-rail shipments could explain a spate of fiery accidents.
In the latest mishap involving fuel produced in an oil patch known as the Bakken, several tank cars exploded after a collision on a desolate stretch of North Dakota track on Monday.
In that case, as with several other accidents in recent months, tank cars exploded with a force that surprised investigators.
The incidents "indicate that the type of crude being transported from the Bakken region may be more flammable than traditional heavy crude oil," the U.S. Pipeline and Hazardous Material Safety Administration said on Thursday.
Officials are examining whether Bakken crude is unduly corrosive, more sulfurous or loaded with explosive gas as it moves on the tracks from oil fields to distant refineries.
On Thursday, Bakken producers were warned to "sufficiently degasify" crude oil being loaded onto tank cars, and officials said they will examine the "dissolved gas content" of crude oil shipments.
Packing gas onto tank cars meant to carry liquid fuels can push the pressure to dangerous levels and provoke explosions, industry officials have said.
"Large amounts of vapor pressure can split the tank, sink the roof and emit (a) flammable gas cloud," the Canadian Crude Quality Technical Association, an industry-sponsored research group, concluded in March.
Bakken producers have recently reported a large amount of corrosion in tank cars and "high vapor pressure causing bubbling crude," the trade group said.
Advances in drilling technology have dramatically spurred oil production in North Dakota in recent years. Over two-thirds of the state's oil production is currently shipped by rail.
Trains carried nearly 700,000 barrels a day of North Dakota oil to market in October, a 67 percent jump from a year earlier, according to the state pipeline authority.
Officials are considering new rail safety rules for crude shipments in light of several spectacular accidents in the United States and Canada.
In July, a runaway oil train carrying light shale crude oil from the Bakken region derailed and exploded in the center of the Quebec town of Lac-Megantic, killing 47 people.
(Reporting by Patrick Rucker; editing by Ros Krasny and Leslie Adler)