The raging wildfire that has laid waste to an area larger than Prince Edward Island and wrecked one-tenth of Fort McMurray was most likely human caused, according to Alberta's senior wildfire manager.

While the investigation continues into the inferno known informally as 'The Beast,' Chad Morrison told the Globe and Mail on Saturday that the fire was probably the result of human action–a broad category that includes everything from careless ATV drivers to issues with power lines.

"Human-caused really means anything other than lightning. It's most likely human caused, but we're continuing to investigate," Mr. Morrison said.

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That's a conclusion local firefighters agree with. While the Fort McMurray fire might not have been intentionally set, human actions were responsible, said Paul Spring, the owner of a local helicopter company that has spent decades fighting forest fires in northern Alberta.

"It wasn't natural," said Mr. Spring of the fire that ignited on May 1. "There was no probability of a fire starting naturally that day. There was no lightning in the forecast, nothing that we look for."

The wildfire is technically known as MWF-009, indicating it was the ninth wildfire of the year in the Fort McMurray area.

The wildfire was first spotted 15-kilometres southwest of Fort McMurray by an airborne forestry crew on May 1. It was discovered during the late afternoon, the peak burning period of the day. There were power lines in the area according to Mr. Spring.

The previous 12 months had been dry in Alberta, with a record-setting drought the preceding summer followed by an unusually dry winter. One fire in northwestern Alberta, spotted near High Level on June 26, 2015, is currently listed as under control but could still be burning nearly a year later.

On the first day of May near-record temperatures and bone dry forests created the perfect conditions for a fire to start.

A wildfire crew landed almost immediately after the fire was discovered and began to tackle the two-hectare fire, which is larger than two Canadian football fields. As the crew approached, MWF-009 was already sending sparks into the sky and leaping to the crowns of tall trees.

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"When a fire starts at that time it moves to a full crown within minutes. It was in the crowns and rolling by the time the helicopters showed up," Mr. Morrison said. "When these fires occur, Mother Nature is going to do what it's going to do. It's going to challenge us."

Complicating matters was a second fire burning at the same time within Fort McMurray near an industrial area in the city's north end. That fire was moving up a hill towards a row of houses on May 1. Mr. Spring says that fire crews had to decide which to tackle first: the fire in a remote area south of town or the one bearing down on homes.

Video from May 1 shows tankers dropping fire retardant in Fort McMurray as helicopters poured buckets of water. Crews had decided to confront the blaze burning in the industrial north end–because it was first spotted within the city it doesn't have a wildfire name like MWF-009.

"The choice had to be made between fire 009 and that second fire headed towards houses. Five out of five times anyone would choose to go after the second fire," Mr. Spring said.

His company wasn't asked to dispatch a helicopter to MWF-009 on May 1. Within two hours that fire had grown to 60 hectares, fed by strong winds. The first evacuation notices went out before dusk that evening.

Fort McMurray's 80,000 residents were evacuated two days later, on May 3.

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Due to the Fort McMurray fire's aggressive behaviour–it jumped the kilometre wide Athabasca River–and the number of dry lightning storms created by the pyrocumulus clouds rising from the inferno, the province will be rewriting part of its wildfire manual, Mr. Morrison said.