(Adds background on an Energy Department study of crude oil in paragraphs 18, 19)
By Patrick Rucker
WASHINGTON, March 31 (Reuters) - New regulations to cap vapor pressure of North Dakota crude fail to account for how it behaves in transit, according to industry experts, raising doubts about whether the state's much-anticipated rules will make oil train shipments safer.
High vapor pressure has been identified as a possible factor 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 rules, which take effect on April 1, aim to contain 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 safety experts say gas levels can climb inside the nearly-full tankers, so the checks are a poor indicator of explosion risks for rail shipments.
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, said Dennis Sutton, executive director of the Crude Oil Quality Association, which studies how to safely handle fossil fuels.
Ametek Inc, a leading manufacturer of testing equipment, has detected vapor pressure climbing from about 9 psi to over 30 psi - more than twice the new limit - while an oil tank is filled to near-capacity. (Graphic: reut.rs/1EHChG4)
About 70 percent of the roughly 1.2 million barrels of oil produced in North Dakota every day moves by rail to distant refineries and passes through hundreds of cities and towns along the way.
The state controls matter to those communities because there is no federal standard to curb explosive gases in oil trains.
North Dakota officials point out that the pressure limit is more stringent than the industry-accepted definition of "stable" crude oil. They also say that they lack jurisdiction over tank cars leaving the state and that the pressure tests are just one of the measures to make oil trains safer.
"We're trying to achieve a set of operating practices that generates a safe, reliable crude oil," Lynn Helms, director of the North Dakota Department of Mineral Resources, has said. Helms has also said that test readings for near-full containers were less reliable.
However, given different testing and transport conditions, industry officials say the pressure threshold may need to be lowered to reduce the risks.
Limiting vapor pressure to 13.7 psi in transit would require an operator to bring it to "something well below that" at the loading point, Sutton said.
The uncertainty about regulatory reach and safety has spurred calls for the White House to develop national standards to control explosive gas pressure.
"Let me be really clear," Democratic Senator Maria Cantwell of Washington state told reporters last week. "They should set a standard on volatility."
The National Transportation Safety Board, an independent safety agency, has already encouraged a federal standard for "setting vapor pressure thresholds" for oil trains citing Canadian findings linking such pressure and the size of explosions in train accidents.
Meanwhile, a leading voice for the oil industry is lobbying Congress to resist federal vapor pressure benchmarks.
Last week, the American Petroleum Institute urged lawmakers to oppose "a national volatility standard" and pointed to an Energy Department study that the severity of an oil train mishap may have more to do with the circumstances of the crash than the volatility of the cargo.
That same report said much more study was needed to understand volatility of crude oil from the Bakken. (For a link to the study: tinyurl.com/nvjqmxt)
The oil industry has said that wringing 'light ends' out of Bakken crude may keep a share of valuable fuel from reaching refineries.
Reuters reported early this month that Transportation Secretary Anthony Foxx took his concerns about Bakken oil volatility to the White House last summer and sought advice on what to do about the danger of explosive gases.
The administration decided that rather than assert federal authority it would allow the North Dakota rules to take root, according to sources familiar with the meeting. (Reporting By Patrick Rucker; Additional reporting by Ernest Scheyder in North Dakota; Editing by Tomasz Janowski, Bernard Orr)