Don Pittis was a forest fire fighter for nearly a decade, and studied forestry at Lakehead University before switching to economics and journalism.

In nearly a decade of being paid to fight forest fires, I rarely experienced the intensity of the fire that the people of Fort McMurray witnessed this week. And while I have felt in terror for my life, I have certainly never seen such economic destruction.

It's not because such giant conflagrations are so rare. It's because firefighters only get that close to the roaring, moving head of a large forest fire when things have gone badly wrong. Canada has thousands of fires every year, but the giant ones seldom come close to communities as big as Fort McMurray.

The leading edge of a crowning fire is always terrifying. The noise is often compared to a passing freight train, but unlike a freight train, the fire cannot be stopped.

Understanding the power of a moving forest fire isn't hard once you think of the process at work.

Firestorm effect

Just like a camp bonfire, the heat of the flames pushes the air into a convection column. When there is little wind, the fire burns straight up, not sideways, creeping slowly through the brush, occasionally flaring up through the needles of a conifer with a bright yellow roar, something called candling. In the absence of firefighters, the fire moves forward gradually, finding new fuel along its edge as the fuel behind the edge smolders to ash.

But powerful winds like those in Fort McMurray can bend the convection column forward so it passes through the crowns of the trees just ahead of the fire front. Instead of candling individually, the fire leaps through the needled crowns even before the fuel behind has finished burning. Then the process is repeated.

Instead of just a thin leading edge of the fire gradually spreading, a wide swath of forest burns at once, flaring up into the sky, throwing up bark, branches, even whole trees.

Firefighters standing in front of the blaze would suffocate as the fire consumes the oxygen and replaces it with smoke. That's why, despite economic damage, they must be pulled out. Water bombers have almost no effect.

Sometimes called a firestorm, such an intense inferno can spread faster still as embers are sent up and then pitched forward by the upper winds. The radiant heat — the reason you have to move back from the campfire when toasting a marshmallow — is so powerful it can ignite trees across a river, road or firebreak.

Morning dawns on the the widespread devastation in Beacon Hill, where 80 per cent of homes were lost as the Fort McMurray, Alta., wildfire rages. (Sylvain Bascaron/Radio-Canada)

Backfiring

As witnesses in Fort McMurray have described, it's the radiant heat that can cause passing vehicles to burst into flames and makes people inside cars feel intense heat despite air conditioning.

Giant fires create their own weather, sucking air along the ground in front of them to feed the convection column. The one way sometimes tried to stop or slow a giant fire is to light another fire in front of it, taking advantage of the surface wind sucked toward the main fire. The intent is to rob the main fire of fuel.

An attempt to use the technique, sometimes called a backfire, was the time I most feared for my life as a forest fire fighter. The trouble is backfires can sometimes backfire, as a shift in wind turns the burnout fire into the new leading edge. We made a run for it between walls of flame, holding hose bags and helmets to shield our faces from the radiant heat.

There is no doubt this is an early beginning to the fire season. Provincial fire crews don't usually gear up until the beginning of May.

Fort McMurray's wildfire destroyed the Denny's restaurant and Super 8 motel. (Briar Stewart/CBC)

Spring fires are special

And spring fires are strange things. Despite hot conditions up on the surface, the ground and deep roots can remain frozen, meaning the trees are not yet flush with water. In spring fires even deciduous trees, normally a partial firebreak, can flare up in eerie yellow smoke.

There is no question that firefighters did what they could. Despite images of the sooty firefighter saving Bambi, human life — including that of the firefighters — ranks as the top firefighting priority, followed by human property and the commercial value of the trees. Animals must fend for themselves.

The good thing about forest fires is they come and go quickly. Just as when you stop adding fuel to a campfire, following the intense leading wall of flame, the interior of a forest is nothing but smoldering ash. You can walk through it in good boots.

The Fort Mac fire may burn on, but the chances of a fire circling around through unburned fuel and taking another pass at the community are tiny. As Canadians pull together to help the people of Fort McMurray, they can only stand in awe, as firefighters do, of the power of nature.

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​More analysis by Don Pittis