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Part 1: Scientists, Missoula County shift wildfire focus to home ignition zone

A crowd gathers to watch a fire burn on Mount Sentinel in this file photo. Recent fires around the West have demonstrated the potential for large urban wildfires. (Martin Kidston/Missoula Current file)

Editor’s note: This is part one of a two-part story on urban fires. Part 2 can be read by following this link

It’s been called an “urban firestorm” or “urban conflagration.” Regardless of the title, the citizens of Superior and Louisville, Colo., all agree that the Dec. 30 fire that burned more than 1,000 homes and businesses nearly to the ground was an urban disaster.

The Marshall Fire started in the grasslands west of the two suburbs as residents were going about their business, some no doubt preparing for New Year’s Eve festivities. They likely wouldn’t have been aware of the fire on an average day when fire departments could snuff out the flames.

But the winds of Dec. 30 were extreme, accelerating down the Rocky Mountain Front with some gusts topping 105 mph. Grassfires burn fast anyway, but this caused the fire to race toward the towns, spitting burning embers ahead of it that then caused several buildings on the edge of town to begin to burn.

From there, the structures themselves started a domino effect, the embers of each penetrating nearby houses, causing entire neighborhoods to burn at about the same time.

Video shows residents emerging from stores, confused and scared, as wind and smoke enveloped the towns. Trying to flee the parking lots, people ended up in bumper-to-bumper traffic as debris bounced off their vehicles. Amazingly, only two people remain unaccounted for.

Post-fire photos show neighborhoods with houses reduced to ash piles, and only the concrete stairwells remain of the four-story Element Hotel. A snowstorm finally blew through on New Year’s Eve, a day too late for the thousands who suddenly found themselves homeless.

Some in Missoula may see the fire as another sad but distant event of 2021. But some fire experts hope people take it as a warning to improve plans for evacuation and home defense.

“Could it happen? Missoula doesn’t have that extent of development yet. But the answer is yes, to a limited extent,” said retired U.S. Forest Service fire behaviorist Jack Cohen.

Dissecting an urban conflagration

Understanding what caused the Colorado disaster is key to reducing the extent of the next one. Four factors played a role, Cohen said: high winds, a wildfire with a wide leading edge and non-fire-resistant structures in relatively dense neighborhoods. And these four led to a final factor: firefighters unable to deal with such an overwhelming situation so buildings burned.

Unlike a point source like a bonfire, a wildfire with a wide fire front can send multiple burning embers into a community, causing a number of house fires to start simultaneously. But those embers aren’t likely to sail far away from the flame front without a good wind blowing them. And stronger winds can create a “blizzard of burning embers.”

“And it doesn’t have to be 100 mph,” Cohen said. “It was 30 to 40 mph winds that spread the West Wind Fire into Denton. And it was the same thing for the Lytton, British Columbia, fire where winds were 25 to 30 mph. And that was a grassfire too.”

The sun sets over Montana in a blanket of smoke. (William Munoz/Missoula Current file)

While it’s not unusual to have high winds along places like the Colorado Front or the plains of eastern Montana, climate scientists are hypothesizing that a warming climate creates conditions that favor more severe storms accompanied by strong winds, which could end up in uncharacteristic places.

Though Missoula isn’t historically a windy town, throughout the night of Nov. 15 , winds toppled trees and power lines in the Missoula area, with the Missoula Airport registering gusts of more than 65 mph while Point Six above Snowbowl hit 75 mph.

If the burning embers rain on a fire-resistant house with a clear “home ignition zone” – an area 100 to 200 feet around the house – little damage is likely to result. But a house with wood siding, large windows and flammable items next to the house, such as leaf litter or firewood, could be in trouble, because the flames will work their way inside the house. A fire department might be able to limit the destruction of one such fire. But put a bunch of similar homes right next to each other, and they’ll not only catch fire but also create their own embers that winds will shower on nearby houses.

“At that point, the community spreads the fire and the wildfire has nothing to do with it,” Cohen said. “Multiple ignitions simultaneously result in fire-involved structures and are completely destroyed because at that point, there’s no fire suppression. What I’ve been trying to get people to understand is fire protection is overwhelmed. And that’s when a community disaster happens.”

Solutions

Cohen has investigated multiple community disasters, carefully observing the scene, noting details that firefighters cannot because they’re too busy trying to save buildings. After seeing similarities in each case, he worked with other fire scientists to devise a more effective fire risk analysis for communities, compared the ability to control wildfire to the ability to control community vulnerability. In essence, they compared trying to control thousands of acres to improving a half-acre of property.

“The ability to be effective is intractable when we define the problem as wildfire,” Cohen said.

In western Montana, residents tend to think of forest fires as the danger to communities. However, as Cohen noted, several recent firestorm disasters have been initiated by grassfires. He can rattle off several such incidents, from the fires last month that ravaged Denton and Gibson Flats near Great Falls to the January 2006 prairie fires in Oklahoma and Texas that burned more than 200 homes. With the Santa Rosa fire in 2017, the Tubbs Fire ran out of stubby vegetation before it reached Coffee Park, but the embers had already inundated the dense subdivisions of Coffee Park.

This is why fire scientists argue that forest thinning does little to nothing to stop wildfire in extreme conditions. Firefighters are pulled back for their safety and firebrands can leap thinned areas. That’s also when urban disasters occur. When conditions aren’t extreme, wildland firefighters can usually put fires out before they reach communities.

The Boulder 2700 fire on Flathead Lake. (Trevon Baker photo)

In 2021, Montana had 2,555 fires, but crews dealt with most of them. Only 48 grew large enough to be named. But some forest managers still justify logging as a way to reduce community wildfire risk. Cohen said such efforts aren’t effective.

“We’re already successful at stopping 95-98% of wildfires. But if we’re not doing preparatory projects to handle the 3% of the fires that are causing us 80-95% of the problems, particularly in light of climate change, then don’t do it. Because it won’t work,” Cohen said. “That seems to be the hard sell.”

When it comes to controlling community vulnerability, it’s a matter of convincing people that all they need to do is improve the conditions in their home ignition zone. And if Missoula wants higher density, then houses need to be built of tougher stuff and designed differently. That’s a lot easier and better for ecosystems than having to clear-cut the forest.

“We need to start thinking in terms of engineering our design and materials, and this can be done with codes,” Cohen said. “And the greater the density, the more important those kind of codes become.”