Why costly forest fires come back to terrorize us: Don Pittis

DonPittiswas a forest fire fighter for nearly a decade, and studied forestry atLakeheadUniversity before switching to economics and journalism.

The latestevacuation of Albertaoilsandsoperations has added millions of dollars to the billions in damage already caused bythe single FortMcMurrayfire that only a few days ago was so calm it had begun to fade from the headlines.

Albertansand other Canadians maybe asking themselves whyfirefightersdidn't get off the pot andput the darn thing out while they had the chance.

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Horrifying pictures taken when the blaze first hitFortMcMurrayclearly show why it's so hard to stop a firein itshottest stages. Perhaps more mystifying is why giant fires so often come back to bite us after we think we're safe.

Fires are so sneaky and unpredictablethat in firefighter lore, among the most dangerous things fire bosses can do for theircareers is to declare a fire under control too soon and have it go on another tear.

A worm's-eye view of how fires burnmakes it clear why thatmistake is so easy to make.

The cost and scale of battlinga giant forest fire is often compared to fighting a war. Thousands of men and womenmust enter the fray.

Despite being manykilometresfrom civilization, the workersmust be housed often in tentsand fed. Despite a lack of roads, they need transportation,sometimes expensive helicopters.And as they get closer to the fire, they must carry everything they need on their backs.

There are few things asexciting as the initial attack on a moving fire. With adrenaline pumping, the crews work long daysflat out, usually attacking the back or side of a fire, setting up aportable pumpatthe nearest river or beaver pond and racing to the fire's edge.

In the boreal forest with its lakes, rocks and swamp, there is nearly always water within pumping distance. But if not, firefighters must attack the edge of the fire with shovels and axes.

Essentially, the technique has two stages.The first pass stops the advancing edge of the fire, putting out the spreading flames with eitherwater or dirt. With smaller fires, when winds are light, the hope is you can work your way from the relative safety of the side of the fire to pinch off the advancing front.

The firefighters' second taskisto use shovels, axes or hoses todiga non-flammablebarrier between the smoldering interior of the fire and the fresh non-burnt fuel outside the fire.

That crucial edge between burntand non-burnt forest fuel is called the fire line. In imagery that echoes the First World War, the job of forest fire fighters is to hold the line. That's what stops the fire. And it's harder than it sounds.

Pussycat to dragon

As we saw this week, a fire's battle plan is never static. Changing winds, falling humidity and rising temperatures can turn a fire that looks like a dozing pussycat into a rampaging dragon.

On a map, the fire's edge may seemlike a straight line, but that's far from the case. Even when it's just creeping or smoldering, the fire moves at different speeds in different types of fuel, creating bays, fingers and islands like the coastline of a boreal lake.

RAW: Aerial view of northern forest fires

9 years ago

Duration 3:20

Fires in the northern forests of Saskatchewan continue to burn. A CBC News camera man shot this video today about 32 kilometres north of La Ronge.

The "fog of war" applies as fire bosses struggle to keep track of the moving fire, workers and equipment. The map of the fire changes constantly and mappers can't keep up.

That's because a fire's advance is inconsistent.It rushes up hills. It creeps down valley sides. It becomes an inferno when criss-crossed fallentrees act like drylogs in a giant fireplace. It slows to a crawl in moistswamps.

Worse, the fire is unpredictable. A change in windcan turn a thinsmoldering finger intothe fire's broadleading edge. The longer the fire remains out of control, the more it becomes multi-headed when a rising wind sends lobes and fingers flaring into fresh fuel.

No more adrenaline

Even as the weather cools, getting a largefire under control is a dreary and laborioustask. There is no more adrenaline, no more overtime pay. Every centimetre of the fire's edge must be painstakingly dug up withhoses and shovels. Working back from the edge, each smoldering stump must be extinguished, each bulldozed pile torn apart.

And then you wait while the deep interior of the giant fire burns itself out.

• Hot spots slow re-entry plans for Fort McMurray
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All the while, the fireline must be constantly patrolled. Many a time I remember patrolling back to find a hidden smoldering root or a deep tuft of moss, a wet spot that had dried out and allowed the fire to escape, merrily burning out into fresh fuel.

Fresh winds can makean interior island of non-burnt forest burst into new flame. Occasionally areas that burned quickly and superficially the first timecan burn againonce fuels have dried out.

And after all the work, all the digging and spraying and smudging, the only way to be sure a big fire is well and truly out is to wait for a long and soaking rain, such that even the forest outside the fire line is so drenched you couldn'tlight a fire if you tried.

Follow Don on Twitter@don_pittis

More analysisby Don Pittis