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Lac-Mégantic crude oil as explosive as gas, testing reveals

First responders fight burning trains after a train derailment and explosion in Lac-Mégantic, Que., early July 6, 2013.


The crude oil that exploded during a derailment in Lac-Mégantic had characteristics similar to that of unleaded gasoline, a new report by the Transportation Safety Board says.

The TSB released the results on Thursday of a battery of tests on crude oil samples drawn from undamaged tank cars pulled from the inferno after the derailment, and from cars from another train that held the same type of oil. The accident occurred when an oil-laden train jumped the tracks and exploded in Lac-Mégantic last July, causing a series of explosions that killed 47 people and levelled the downtown core.

That disaster, along with a string of other fiery derailments involving crude oil, has led to growing concerns about the safety of shipping crude by rail. A Globe and Mail investigation has documented how oil from the Bakken formation, which straddles North Dakota, Saskatchewan and Manitoba, can be more volatile than other crudes, which means it is more likely to explode if an accident occurs.

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Last fall, the TSB said the oil on the Lac-Mégantic train, which was from the Bakken region, had been incorrectly classified as "packing group III," the least dangerous option for crude oil. The TSB test results show the oil should have been classified as a more dangerous flammable liquid, in part because its flashpoint was significantly lower than that of crude typically pulled from other North American sites, such as the Alberta oil sands.

The flashpoint refers to the temperature at which the crude gives off enough vapour to ignite in air, with a low flashpoint increasing the likelihood that crude would explode during a rail accident. The TSB results indicate that the flashpoint on at least some of the crude in the Lac-Mégantic accident was so low that the machine used to measure it could only show that it was less than -35 C. "It is apparent that the occurrence crude oil's flashpoint is similar to that of unleaded gasoline," the report says.

The test results also indicate that the crude had a high vapour pressure, another factor that would make it more vulnerable to exploding during an accident.

A recent Wall Street Journal analysis of test results for oil from a number of different locations suggested that Bakken crude generally has a higher vapour pressure than many traditional crudes. The TSB's test results indicate that the crude in the Lac-Mégantic disaster had a slightly higher vapour pressure than the Bakken samples analyzed by the newspaper.

The high vapour pressure and low flashpoint of the crude in Lac-Mégantic meant it was "readily ignitable," the TSB report says. "Multiple sources of ignition were present at the derailments site … Therefore, all of the conditions required for ignition to occur were present."

Transport Minister Lisa Raitt ordered companies last year to test all crude before it is shipped to make sure it is classified correctly. The U.S. issued a similar order on testing last month, and took the additional step of prohibiting companies from classifying crude in the least-dangerous category, even in cases where test results suggest it is not highly volatile.

The results of the classification tests can determine which tank cars may be used for crude shipments and how shipping documents that accompany a train should be filled out.

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On Thursday, U.S. regulators amended their order by narrowing the scope of the new requirements. The change means shippers would have to measure the flashpoint and boiling point of the crude they are shipping, but would not have to measure other crude specifications such as vapour pressure and corrosivity, as long as they are familiar with the characteristics of the oil.

The Canadian directive on testing does not specify the types of tests that must be run, but flashpoint and boiling point are the key factors in determining how shipments in Canada are classified. Ottawa took steps earlier this year to close a perceived loophole in the rules by introducing changes that would require companies to vouch for the contents of crude oil and keep detailed records of test results for at least two years.

With a report from Reuters

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