A few days ago, Fort McMurray was a mid-size Canadian city. Today, it is burning down, after unseasonably high temperatures, low humidity, and strong winds turned a trailer park fire into a city-wide conflagration.
Eighty thousand people have been evacuated, and 250 firefighters are attacking an inferno that has consumed 1,600 buildings. "Now it’s to the point that this fire is creating its own weather pattern," says Shayne Mintz, regional director for Canada's National Fire Protection Association. And that's not all. The fire has spread into the forests around the city, creating an insane logistical challenge for the women and men fighting to save what remains.
Fighting this fire is especially complicated, because it’s not confined to just a city or wilderness. Fort McMurray is in what firefighters call a Wildland Urban Interface. Forest surrounds and laces through the city. Some of its neighborhoods are built on slopes, hilltops, and other topographic features that channel fire. The city is isolated, with a single freeway connecting it to the outside world. Oh, and it’s in the middle of the Alberta Tar Sands.
The fire started in the woods outside town, and burning embers blew into a mobile home park1, setting it ablaze. Once the first trailer lit up, there wasn’t much of a chance to save nearby trailers, made with their lightweight materials. “These are very combustible," says Jim Connors, director of City College of San Francisco's fire science technology program. "If one catches fire it is very easy to spread to other mobile homes."
Outside the mobile home park, firefighters have a better chance of saving buildings, but they can’t save everything. What happens next, especially in a complicated, tinder-filled city like Fort McMurray, is a kind of firefighting triage. If a structure is especially at risk—or puts firefighters at risk—it’s probably getting left to burn. “This comes down to how it’s built, where it’s sitting on a hill, and what’s around it," says Connors.
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First to go are the homes whose owners didn’t clear away surrounding vegetation, which are especially flammable and dangerous for firefighters. But other homes are at risk because of Fort McMurray’s topography. Fire loves to climb hills, and several of the city's neighborhoods are elevated. Flames also pick up momentum when they encounter pinched-in sections between two slopes—so much that firefighters call these vertical depressions chimneys. And the saddles between two hills can act like funnels, compressing the fire and increasing its intensity. "If you're not aware, you could be in some of these natural features that promote spread," says Connors.
The defendable homes—those with a brush-free fire boundary, and leafless roofs and rain gutters—get treated with flame retardant chemicals.
The firefighters try to get in front of the blaze, setting up gaps with no fuel to burn. They’ll set up perimeters around savable buildings, hitting them from above and below with water. "If you got one city block you try to hold it," says Tim Capehart, director of fire science safety at Bakersfield College in California. "If you’ve got two or three blocks, then you’re moving further out."
That’s protecting the city. But in Fort McMurray, firefighters have an even bigger challenge in trying to suppress the fire in the forest—because that’s all fuel, waiting to burn. Especially these trees. The spruce and pine in northern Canada are adapted to burn, and the unseasonably heat and low annual snowpack has turned them into a tinderbox.
Once you’re in the forest proper, standard wildfire tactics apply. Dig trenches upwind of the fire, then start small backfires to eat up the fuel between the main conflagration and the fire breaks. Use air support to drop water from above. Repeat until the fire stops, or the fire stops you.
Surrounding Fort McMurray’s tinderbox are tar sands, oil fields, and mines. Shayne Mintz, the Canadian fire protection director, says nobody is worried about the blaze reaching them—yet. "All those areas are still a bit north or outside the fire zone right now," he says. Many of them are being used as temporary camps for evacuees.
But the fire is still completely unconfined. A wind shift or some other unforeseen event could change the game. "The tar sands are not flammable, but they are combustible," says Capehart, whose college campus in Bakersfield sits over one of the largest oil fields in the contiguous United States. The difference, he says, is flash point. As opposed to gasoline, which will light with a match, tar needs to get hot enough to produce vapor. The tar vapor is what burns, and it’s incredibly difficult to extinguish.
Everyone will have to wait for the smoke to clear to find out what has truly become of Fort McMurray.
If the tar sands do combust, the Fort McMurray firefighting strategy will dramatically shift. "There's three things that you need to make a fire: oxygen, fuel, and heat. If you take one away, physics forces the fire to go out," says Capehart. Firefighters attack oil and tar fires with special foam that coats the tar's surface, effectively separating the vapors from the oxygen. Drilling sites and mines are typically required to have this stuff on hand, but are loathe to use it because of environmental concerns. Fighting a tar fire is like playing the pyrrhic lottery.
In summary, Fort McMurray is currently looking really screwed. The airport and hospital are both closed. The one freeway leading out of town is backed up with miles of traffic, confounding not only the evacuation, but also efforts to bring relief. Meteorologists are predicting a cold front, but not cold enough to provide firefighters any meaningful aid. The one positive note is there have been no casualties, no fatalities. At least, not yet. Everyone will have to wait for the smoke to clear to find out what has truly become of Fort McMurray.
1 UPDATE 05/05/2016 Originally sources had indicated that this fire began in the mobile home park itself, under unknown circumstances.