By Chester Dawson 

Canadian regulators said Thursday the improperly labeled oil on a train that derailed in a Quebec town last July and killed 47 people was consistent with normal light sweet crude and was as volatile as gasoline, highlighting the potential danger of crude-by-rail shipments.

The analysis marks the first time government officials have tested the doomed train's oil, from North Dakota's Bakken shale fields, which they have said was improperly labeled because it was more volatile and had a lower ignition point than indicated by its shippers.

In response to the accident, regulators in the U.S. and Canada have mandated new testing requirements for oil shipped by rail.

The engineering lab report released by Canada's Transportation Safety Board on Thursday found tests of oil samples showed properties that were "consistent with those of a light sweet crude oil, with volatility comparable to that of a condensate or gasoline product." The samples were taken from cars that didn't explode at the accident site and another train carrying oil of the same origin.

The analysis also said a number of factors contributed to the massive size of the explosion, which destroyed several buildings in the town of Lac-Mégantic, and shocked oil and rail industry officials.

"The large quantities of spilled crude oil, the rapid rate of release, and the oil's high volatility and low viscosity were likely the major contributors to the large post-derailment fireball and pool fire," the report said.

The TSB report appeared to rule out chemicals used in shale oil fracking as a cause for the explosion, which some had speculated might be a contributing factor in the ignition of the crude or the intensity of the fire. "There was no indication that the...crude oil's properties had been affected by contamination from fracturing process fluid additives," the report said.

It also determined that levels of hydrogen sulfide, a toxic gas often dissolved into crude oil, was not found to be present in the oil sampled, but that "significant concentrations" of benzene and other volatile organic compounds were detected.

A Wall Street Journal analysis published last month found that North Dakota's Bakken Shale formation contains several times the amount of combustible gases as oil from elsewhere. It also found that light, sweet oil from the Bakken Shale had a far higher vapor pressure--making it much more likely to throw off combustible gases--than crude from dozens of other locations.

The TSB released its analysis as part of a larger investigation into the derailment of the Montreal, Maine & Atlantic Railway Inc.-operated train that careened off the tracks on July 6 after an unexplained brake failure.

TSB spokesman Chris Krepski said that the investigation remains ongoing and a final report that will detail the agency's findings is pending.

Dangerous fluids are measured on a scale of 1 to 3, with level 1 being most hazardous. The TSB lab report concluded that all of the crude sampled met the criteria for classification as level 2. Investigators had said in September that trucks used to move the oil from Bakken to a rail-loading facility in North Dakota had documents indicating level 2, but that the railcars that took the cargo on to Lac-Mégantic had identified it as level 3.

The MM&A train was headed to an oil refinery in St. John, New Brunswick, owned and operated by closely held Irving Oil. Investigators have said regulations dictate the importer of the goods--in this case, Irving--has the responsibility to ensure railcars are properly labeled.

Last month, the U.S. Transportation Department issued emergency rules requiring more extensive testing of oil shipped by rail, following similar directives by Canadian authorities.

A spokesman from Canadian Pacific Railway Ltd. declined to comment on the TSB report. Representatives for Canadian National Railway Co. were unavailable for immediate comment.

Paul Vieira and David George-Cosh contributed to this article.

Write to Chester Dawson at chester.dawson@wsj.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires

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