A trailer park damaged by the wildfires is seen in Fort McMurray, Alta., on Monday, May 9, 2016.

Image Credit: THE CANADIAN PRESS/Ryan Remiorz

CALGARY - Crews are working around the clock to restore power and natural gas to the fire-ravaged city of Fort McMurray, but the head of the utility that serves the area says it's impossible to say how soon residents will be able to go home.

It's slow and dangerous work.

"If you can imagine a charred power line pole that we don't want to take out of service, but we want to reinforce — it's something we obviously want to do with great care," Atco president Siegfried Kiefer said Wednesday following the company's annual meeting.

"Both of the products we deal with are invisible and both can kill you."

More than 80,000 people were forced to flee when a ravenous wildfire attacked several neighbourhoods in the northern Alberta city last week.

The blaze destroyed about 2,400 structures, but about 90 per cent of the city was saved.

Kiefer said about 75 per cent of Fort McMurray's buildings could have their power turned back on, but at this early stage it wouldn't be safe.

"We won't turn power on to many of the regions until inspections are complete," he said.

"Obviously you don't want to if there's any residual gas or if there's any kind of explosion potential."

As for natural gas, Atco cut off the supply to the city when the fire started as a safety precaution, Kiefer said, and turning it back on can't occur until gas lines are checked.

Alberta Premier Rachel Notley didn't have an update Wednesday on when Fort McMurray residents may be able to go back. Earlier in the week, after touring the city by ground, she said a schedule would be out in about two weeks.

"I understand it's hard for people not to have a definitive timeline," she said. "But at the same time, I don't want to give them a definitive timeline, have them build their hopes around that ... and then discover an infrastructure deficit that we didn't previously know about that delays things by a week or two."

Kiefer said he couldn't pinpoint how soon repairs will be completed, but suggested it would be "less than a month."

Once they are, re-entry is likely to be staggered, he said.

"That's how it worked in the Slave Lake fires. We took blocks of communities and allowed members of that area of the town to come in."

Atco also has a division that provides modular buildings, office trailers, workforce housing and camp and lodging services.

Kiefer said once first responders are done their work, the company will be making the most of 4,000 beds it already has available in the Fort McMurray area.

Atco is also willing to "ramp up" delivery of additional temporary housing if the province decides it's necessary for people returning to the city while their houses are rebuilt.

News from © The Canadian Press, 2016