WASHINGTON - International rules for handling the kind of petroleum shipments involved in several recent fiery derailments may need to be revised, the United Nations said, in a move that could rattle the fast-growing oil-by-rail sector.

A U.N. panel for shipping hazardous materials this week said that it accepted a request from U.S. and Canadian experts to revisit rules that govern shipping the kinds of fuel produced in energy areas such as North Dakota's Bakken.

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Specifically, the panel will examine whether rules for shipping crude oil properly account for dangerous pressure and volatile gases.

"Unprocessed crude oil may present unique hazards based on the specific gas content, posing different hazards in transport," the U.N. panel on transporting dangerous goods said in a statement seen by Reuters.

Existing hazardous material rules envision a test for the initial boiling point of crude oil and the liquid's flash point, or the temperature at which it will combust with a spark.

But the rules do not require a test for pressure and the panel will consider whether that is a blind spot in the regulations that should be addressed.

U.S. and Canadian officials have been trying to understand the potential dangers of oil-by-rail shipments since a 74-car runaway train carrying Bakken crude exploded in Lac-Megantic, Quebec, last July, killing 47 people.

"This is massive," said Lawrence Bierlein, a veteran transportation lawyer in Washington.

"If it succeeds, this is going to change the definition of flammable liquids in a way that is going to hit the oil industry and many others."