OTTAWA — A runaway train that blew up in a Quebec town, killing 47 people, was hauling a more flammable, gasoline-like fuel than the crude oil it was supposed to be carrying, raising questions about how accurately dangerous goods are identified on North American railroads, Canadian investigators said on Wednesday.

In an update on its probe into the July 6 disaster, Canada’s Transportation Safety Board urged U.S. and Canadian regulators to better document the transport of dangerous goods and said it is also looking at the safety of the rail cars that are used to move oil. The TSB can recommend changes but not impose them.

The tanker train derailed and exploded in the middle of the small town of Lac-Megantic, Quebec, causing hundreds of millions of dollars in damage as well as the 47 deaths in what was the continent’s deadliest rail disaster in two decades.

The calamity focused attention on rising volumes of crude-by-rail shipments across North America, which have gained in popularity as pipelines fill to capacity.

The fuel being shipped through Lac-Megantic by the now-bankrupt Montreal, Maine and Atlantic Railway came from a U.S. Bakken oilfield and was headed for an Atlantic Canadian refinery. The TSB said documents showed the cargo belonged to the Packing Group III category, which describes regular crude oil.

But tests showed the oil actually belonged to the Packing Group II category, which has the characteristics of gasoline and is much more explosive.

“The lower flashpoint of the crude oil explains in part why it ignited so quickly,” TSB chief investigator Donald Ross told a news conference.

The TSB made clear the cargo would have been handled the same way, regardless of fuel classification, under current rules. Its investigation will now shift to the cars used on the train: old-style DOT 111 tanker cars, which lack twin hulls or extra strengthening.

Asked if the TSB might recommend that companies be banned from using the older versions of the DOT 111 to carry fuel, investigator Ed Belkaloul replied: “Our inquiry continues and based on the results, it’s a path we’re contemplating, and eventually if we find deficiencies, we’ll go in that direction.”

The driverless train, hauling 72 tanker cars, was parked uphill of Lac-Megantic when it rolled away, accelerated on a downhill grade and derailed and exploded in vast fireballs in the center of town.

The gigantic blasts already had raised questions about the cargo, given that regular crude oil does not normally explode very readily. Bakken crude is lighter, and hence more volatile, than crude from some other areas.

Ross said the fuel had been taken by truck from 11 Bakken wellheads to a train yard in North Dakota. Shipping documents from the truck companies that the TSB saw showed the fuel had been correctly listed as PGII. But when the train left, the classification had somehow changed to PGIII, he added.

Asked how that could have happened, Ross answered: “Good question.” Tests on a tanker train that was following the one involved in the disaster on the rail line showed that it too was carrying PGII fuel that had been documented as PGIII.

Deborah Hersman, acting chairman of the U.S. Transportation Safety Board, said she shared the Canadian TSB’s concerns.

“Clearly understanding the hazardous characteristics of what is being transported is one of the keys to safe transportation,” she said in a statement.

Canadian Transport Minister Lisa Raitt noted that if a company does not properly classify its goods, it can be prosecuted.

Ross said that stronger tanker cars might not have helped much in Lac-Megantic.

“I think you have to bear in mind the speed of this accident … given the speed the train came down the hill, was the performance of the cars reasonable? Obviously you can’t build a railway car to withstand anything,” he told reporters.

Environmental organization Greenpeace demanded an immediate ban on shipping oil in the older DOT 111 cars.

“What we learned today was that there are major gaps in the safety rules for moving oil by rail,” said climate and energy campaigner Keith Stewart.

Canada’s federal transport ministry reacted to the disaster on July 23 by saying trains carrying dangerous goods must not be left unattended on a main track, and two “qualified persons” must run any train that hauls dangerous goods.

The train in the Quebec crash had a single engineer aboard when it was parked for the night on the main line.