Thick plumes of black smoke billowed from the wreckage site in Wapske after crews detonated explosive charges placed on the hulls of the cars in order to allow vapour and gas to burn off in a wooded area.
CN spokesman Jim Feeny said the explosion was carried out by the rail company and a crew from Louisiana with expertise in cleaning up derailed tankers.
The procedure, known as a vent and burn, was used on two tanker cars carrying liquefied petroleum gas that were burning prior to the explosion and a third one with the gas in it that was not on fire. Feeny said the fire from the explosion was still burning more than four hours after it started, but added the experts overseeing the operation said it was progressing as planned.
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 would 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."
Some tanker cars that derailed from the CN (TSX:CNR) freight train have been burning since Tuesday night at the scene of the derailment, near Plaster Rock.
Feeny said fires from diesel fuel in a locomotive that derailed and a tanker car that was loaded with crude oil were no longer burning.
An evacuation of the area has affected about 150 people since the derailment of 19 rail cars in the 122-car train, and there is no definitive word on when they might be allowed to return to their homes.
A resident who attended a public meeting Friday night said they were told it's possible they could go home this weekend.
"Basically that we might be back in our houses this weekend, might be," said Lyla Bear-Tatlock. "It's according to how everything goes with the clean up overnight and tomorrow."
Some of the evacuees have been allowed to temporarily return to their houses to check on their property and pets.
Laurie Beaulieu, another evacuee, said she was not overly frustrated from being away from home and appreciates the work crews have to do.
"They have a job to do and I'd rather go home when it's safe than go back too soon and have to leave again," said Beaulieu, 41.
A senior investigator with the federal Transportation Safety Board said Thursday that they found a cracked wheel and broken rail at the scene of the derailment, but cautioned that it's too early to determine the exact cause.
Feeny has said that based on its preliminary investigation, the company believes a wheel and possibly an axle failure caused the derailment.
The province's Health Department said as a precaution, people in the area with private wells should not drink their water until after they have been tested.
Feeny said CN will cover the costs of the cleanup and compensate those whose properties have been damaged and incurred expenses as a result of the evacuation.