Investigators say the huge fire that destroyed a Fort McMurray condo complex under construction started when machinery struck a gas line.

Assistant deputy chief Jody Butz said a soil stabilization mixer tore a 15-centimetre gas line, releasing gas into the air before also hitting the building’s main power, telephone and cable lines causing a spark that ignited the building.

Although the building had a sprinkler system installed, it was not yet working.

It took three hours for fire crews to get the flames under control. One firefighter received minor injuries while battling the blaze, but is expected back at work within a few weeks.

Butz said the building had been slated for low-income housing and noted it had been nearing completion when the fire struck.

Although no exact estimate for damages has been made, Butz said the cost will likely be in the millions.