Industry experts stated that new regulations framed to cap vapor pressure of North Dakota crude failed to account how it behaves in transit.

This failure has raised concerns about whether the state's much-anticipated rules will make oil train shipments safer, they said.

High vapor pressure has been identified as a possible reason in the fireball explosions witnessed after oil train derailments in Illinois and West Virginia in recent weeks.

For over a year, federal officials have warned that crude from North Dakota's Bakken shale oilfields contains a cocktail of explosive gas known in the industry as 'light ends'.

The new rule that will go into effect from April 1, aims at controlling dangers by spot-checking the vapor pressure of crude before loading and capping it at 13.7 pounds per square inch (psi) about normal atmospheric conditions.

The plan relies on a widely-used test for measuring pressure at the wellhead. But as per safety experts, gas levels can rise inside the filled tankers therefore the checks are a poor indicator of explosion risks for rail shipments.

Dennis Sutton, executive director of the Crude Oil Quality Association, said, "It is well-understood, basic physics that crude oil will exert more pressure in a full container than in the test conditions North Dakota will use".

It has been told that Ametek Inc, a leading manufacturer of testing equipment, has detected vapor pressure climbing from about 9 psi to over 30 psi, which is twice that of the new limit.

About 70% of the roughly 1.2 million barrels of oil produced in North Dakota every day moves by rail to far located refineries and passes through hundreds of cities and towns along the way.