A huge fireball and black smoke billowed from the site of a CN Rail train derailment near Plaster Rock, N.B., Friday as officials performed a controlled burn.

A team of experts used explosive devices to burn and vent three butane-filled rail cars at about 3:45 p.m. AT. CN spokesman Jim Feeny said fire from the explosion was still burning more than four hours after it started, but experts overseeing the operation say it was progressing as planned.​

Feeny said the explosion was carried out by the rail company and a crew from Louisiana with expertise in cleaning up derailed tankers.

The flames were visible from about five kilometres away.

Feeny said the intent behind the explosion was to allow crews to move cars safely. It's the same type of explosion that was used following a CN train derailment in Gainford, Alta., in October.

Crews will work through the night, he said, to begin the clean up of the site, including work to rebuild the track, and arranging to move what's in the cars.

"The next step will be a transfer of product," Feeny added.

“There are other cars that were never involved in the fire that are containing products that will have to be transferred from one car to another or to a truck so those products can be removed."

"The burn is needed so that evacuees may return to their homes as soon as possible," the Department of Public Safety's Emergency Measures Organization (EMO) stated in a release. "The safety of residents remains the priority."

There is still no indication when the evacuees will be allowed to return to their homes. But without the controlled burn, the butane could have continued burning for a week or two, officials said.

The procedure is rare but safe, CN officials said. It has only been used about four times in Canada before, CBC's Melissa Oakley reported from the scene.

About 150 people living in 50 homes within a two-kilometre radius of the derailment site in Wapske have spent three nights out of their homes since the Tuesday night derailment. Most are staying with family or friends.

A CN Rail train hauling crude oil, propane, butane and other goods derailed about 7 p.m. Tuesday, sparking a massive fire in some of the derailed cars that continued to billow smoke into the rural area on Friday.

The materials posed a hazard to residents, inspectors and salvage workers.

Safest option

A liquefied petroleum gas emergency response team brought in from Louisiana assessed the situation on Thursday and deemed the controlled burn the safest option and the quickest way to get evacuees back home, said Oakley.

Crews set charges on the top and bottom of the cars, which punched small holes in the hulls of the cars, said Jim Feeny, director of public and government affairs for CN Rail.

That allowed the vapour and liquid at the bottom of the cars to escape, ignite and burn off, he said.

"The fire will be extinguished, the cars will be removed and then things will start returning back to normal," said Feeny.

The EMO had advised earlier in the day the public might see the flames at the derailment site become temporarily larger as part of the technique to extinguish the fire. 

The department said people would likely hear sirens but should not be alarmed.

Several people gathered to watch the event, reported Oakely. The fireball was "impressive," she said.

Transportation Safety Board investigators said 19 of the train's 122 cars derailed, along with a remote locomotive.

The derailed cars included five that were full of crude oil and four that contained liquefied petroleum gas.

Evacuees were updated on the situation in a private meeting Thursday afternoon. There is no indication when the evacuation order will be lifted.

Residents check on homes

Residents with wood-burning heating systems in their homes were being given escorted visits to their homes to check on the state of things.

"I'll feel better once I get to my house and check it out and see if my water's frozen," said resident Richard Levesque on Thursday as he waited for an escort. "It hasn't had any heat in it since last night.

Plaster Rock derailment

"That's why I'm trying to get to it now … to get the furnace going, make sure the pipes aren't froze."

Two full days after the derailment, the burning crash site was still too dangerous for investigators to approach.

It was confirmed that two of the tank cars were older model DOT-111s, which have a history of rupturing during accidents. DOT-111s were also involved in the Lac-Mégantic, Que., derailment disaster in July 2013 that killed 47 people when a crude-carrying train derailed in the middle of the town and set off a series of explosions and fires that lasted for days.

"The Transportation Safety Board and the U.S. regulator have been warning for years these tank cars have a tendency to puncture easily during derailments and nothing really has been done about it," said Bruce Campbell, executive director of the Canadian Centre for Policy Alternatives.

Opposition Leader Tom Mulcair said it's time for the federal government to change the rules.

"There are some cars that are safer than others," said Mulcair ."There's a new generation that are required in the [United] States. We should be using those."

Lead investigator Guy Laporte of the TSB said on an initial visit to the site Wednesday, he saw that a wheel had cracked on one car toward the front of the train and moved on its axle, falling to the ground inside the rail. A broken rail was also noted.

The other derailed cars were at the rear of the train. That was the scene of the fire and remained too dangerous for Laporte and investigators to approach on Thursday.

In both the Plaster Rock and Lac-Mégantic derailments, the crude oil was destined for the Irving Oil refinery in Saint John.

More crude oil carried by trains

hl-train-wheel

This cracked wheel slipped on its axle on the train that derailed near Plaster Rock, N.B., on Tuesday. (CBC)

Court documents filed in connection with a lawsuit in the Lac-Mégantic derailment show MM&A railway hauled 67 trains bound for the Irving refinery between Nov. 2, 2012, and July 6, 2013. Florida-based World Fuel Services helped Irving import 3,830 tanker cars of crude oil during that time period.

Campbell notes the volume of crude oil carried by train in Canada has skyrocketed in recent years, from 529 cars in 2005 to an estimated 160,000 cars last year.

Campbell says the regulatory process hasn't kept up with that growth.

"The number of inspectors for the transportation of dangerous goods has remained pretty steady at 35 inspectors," said Campbell. "And my calculation is that the ratio of inspectors to car loads of oil has gone from one in 14 to one in 4,000 over that period."