Oil industry studies concluding that Bakken crude oil is safe to move by rail under existing standards may underestimate the dangers of the fuel and should not be the last word, U.S. lawmakers and industry officials said on Monday.

In the past year, several doomed oil trains originated from North Dakota’s Bakken region, including a shipment that jumped the tracks and burst into flames in Lynchburg, Virginia, on April 30. Last July, a fiery derailment destroyed the center of the village of Lac-Megantic, Quebec, killing 47 people.

Two industry-funded studies conclude Bakken fuel is rightly classed as a flammable liquid that can safely move in standard tank cars. The cargo is nothing akin to flammable gasses like propane that must move in costlier, heavier vessels, the oil industry has said.

But the industry findings hinge on incomplete and out-of-date methods for determining vapor pressure, an important indicator of volatility, that may miss the true dangers of Bakken fuel, according to several industry officials.

Lawmakers say they expect regulators to scrutinize the industry’s findings.

“These studies should be taken with a grain of salt,” said Senator Charles Schumer, Democrat of New York, a state that is a major pass-through point for Bakken fuel.

One study released May 20 by the North Dakota Petroleum Council (NDPC) collected samples with open bottles rather than a precision instrument, known as a floating piston cylinder, that is being adopted by the industry.

Gas can escape with bottle sampling and such tests are unreliable, said the Canadian Crude Quality Technical Association, a trade group.

“We would consider the data suspect,” the group said.

ASTM, an international standard-setting body, last month deemed the floating piston cylinder the right tool for Bakken fuel samples. Open bottle samples can skew vapor pressure nearly 10 percent lower, according to research from Ametek, which manufactures testing equipment.

Industry officials say that any underestimation of vapor pressure would be negligible.

Vapor pressure results did not exceed 15 pounds per square inch (psi) in the NDPC report.

A separate study by the American Fuel and Petrochemical Manufacturers (AFPM) returned readings below 17 psi.

The threshold pressure for flammable gas is 43 psi under those same conditions.

Rich Moskowitz, general counsel for the AFPM, the refining industry trade group, said its report “clearly found that Bakken crude oil is properly transported as a flammable liquid. That’s the bottom line.”

Industry officials note that the U.S. Department of Transportation has not issued any of its own findings on Bakken fuel despite collecting samples since the summer.

The issue was expected to be raised Tuesday at a panel of the Senate Commerce Committee which had scheduled testimony from railroad regulators, among others.

“It is my hope that any private data collection and studies on this issue will be highly scrutinized,” said Senator Cory Booker, Democrat of New Jersey, who sits on the panel. (Reporting by Patrick Rucker; Editing by Grant McCool)