The Wall Street Journal reported yesterday that questions have arisen about the accuracy of scientific tests used to write the regulations. Lynn Helms, head of the state Department of Mineral Resources, said the proposal is still sound despite the concerns about the tests.

“These rules are part of a commitment we made to the federal government to do our part” on oil safety, Helms said.

Oil from the Bakken Shale has caught fire following a string of derailments and other rail accidents, leading to concerns that it’s more prone than other types of oil to ignite in an accident. One fire last summer killed 47 people in Lac-Mégantic, Quebec.

Separately, the U.S. Transportation Department is considering tougher construction standards for rail cars.

North Dakota’s proposed rules are intended to lower a measurement of volatility known as Reid vapor pressure. If they’re approved, operators will have to take steps to ensure that vapor pressure of any oil shipped by rail is below 13.7 pounds per square inch. Most companies would be able to comply by using existing equipment to heat oil and release volatile compounds like propane and butane.

In other parts of the country, oil companies build more extensive plants known as stabilizers to separate volatile compounds from crude oil. The plants are relatively rare in North Dakota, and the state rules are designed to help operators avoid the cost of new plants.

North Dakota based its regulations on a study conducted by the North Dakota Petroleum Council, which found that the vapor pressure of Bakken oil didn’t vary significantly from other types of crude.

Scientists including an engineer from Exxon Mobil Corp.’s Canadian subsidiary and a Canadian trade association said the North Dakota study used a flawed test method, the Journal reported.

The study relied on tests taken on oil in an open container, which could allow volatile chemicals to evaporate before being detected — the equivalent of measuring the fizz in soda after opening the bottle. They suggested using other tests that measure how the oil behaves in a closed container.