Built to Burn

The Santa Ana winds of Southern California are sometimes called the “Devil Winds.” They pick up in the late summer and early fall, sweeping down from the mountains and across the coast. They’re hot and dry, and known for creating dangerous fire conditions.

In late November of 1980 — as the Santa Anas blew in at up to 90 miles an hour — an unknown arsonist lit a fire near Panorama Point in the San Bernardino Mountains. Pushed by the wind, the fire grew and quickly spread down the mountain toward the city of San Bernardino.

In just a few hours, the Panorama Fire destroyed hundreds of homes and killed four people. It was one of the worst wildfire disasters in California history at the time, which sent one man off on a mission to try and change the way we address wildfires.

Burning Mystery

Jack Cohen was a few years out of graduate school, and a recent transplant to California at the time of the fire. He was working as a research scientist for the Forest Service, studying fire behavior, and he was interested in how the Panorama fire had destroyed so many homes — especially when there was such a robust firefighting response.

One of the first things that Cohen did was to listen to emergency dispatch tapes from the day of the fire. And as he listened, he began to notice a pattern. People were calling in about houses on fire long before the fire front ever reached their neighborhoods.

The houses were not burning because a wall of flames was racing through the community, destroying them. It was something else: embers. As wildfires burn, they generate embers that are lofted downwind ahead of the main body of the fire. And Cohen realized that most of the houses that burned had one, extremely problematic feature in common: the embers were accumulating in the crevices around their dry wood shingle roofs, and setting fire to the houses from above.

Across the street, in a development without wood roofs, most of the houses had survived. The problem was that some houses were built to burn.

It wasn’t a huge revelation that wood roofs were flammable — people had known that for ages. But for Cohen, it was a big moment. Because when he shifted his focus to the design of the homes, suddenly he found himself wondering if we were framing the whole problem of wildfire in the wrong way. Cohen wasn’t the first to have that thought, but he was the first to do extensive research into exactly how homes burn in wildfires.

His subsequent work would put him at odds with some of the main fire fighting agencies in the U.S., as well as with hundreds of years of fire policy and tradition.

Fire = Bad

For most of this country’s history, our approach to wildfire could be summed up as “fire is bad.” Before colonization, many Native American tribes set fires intentionally to regenerate wild plants and to create grasslands, and habitat for game. But when Europeans arrived, they brought fear of fire with them.

Over time, in much of the country, not only did we do away with the practice of setting fires, we actually started to extinguish naturally-occurring fires too.

In 1911, that became an official responsibility of the newly-created Forest Service. Later, in 1935, that policy even got a name — the “10 AM rule.” It said the Forest Service should put out every new fire on public land by 10 AM the following day. For a while, that brute-force approach seemed to work.

But these early fire fighters had an advantage. For millennia — before the rise of modern fire suppression — wildfires had burned regularly through America’s forests, eating up all the fuel. So when there were fires, they were often low-intensity and stayed on the forest floor.

But then the forest began to get thicker and thicker — so when it did catch on fire, there was more material to burn… and the fires burned hotter and bigger. Effectively, by suppressing natural fires… we created something that turned out to be much, much worse.

Trailblazing Research & Redesign

Which brings us back to Jack Cohen and the Panorama fire. Once he started to focus on the home as the problem, not the wildfire, he wanted to know what made some houses more susceptible than others. “What I’m trying to do is to establish a relationship between wildfire and home destruction. I want to know what that linkage is. How does this happen?”

He set about learning all of a house’s potential weaknesses — all the ways it might plausibly catch on fire. He did a series of experiments, including one in the late 1990s in northern Canada where he set an actual forest on fire. Cohen cut plots of forest and set them on fire to watch them burn.

What Cohen found in the experiment was that an entire forest could be on fire, 30 feet away from the house… and nothing. It was fine.

But of course, Cohen knew that radiant heat and flames weren’t the only threats to a house. There were also the embers. He frequently found himself standing next to houses reduced to ash with green trees sitting right next to them. It was a telltale sign that the fire front never even reached the home, but the embers had.

So, he did experiments to see exactly how the embers were setting houses on fire, and he discovered embers like to collect in lots of places — like in the corners of wood deck, and in gutters full of pine needles, and in attics with open vents.

The more Cohen thought about it, the more he came to believe that most ember fires could be stopped with some simple design solutions.

He started by drawing a buffer, based on a conservative interpretation of those Canadian fire experiments. He called it the “home ignition zone.” The home ignition zone is limited to the house and its immediate surroundings out to about a hundred feet.

Between 100 feet and 30 feet from the house, Cohen said, the goal is to keep trees spaced in a way that prevents the fire from jumping from tree to tree, and forces it onto the ground. Between 30 and 5 feet, the goal is to landscape and design so the ground fire loses steam, by removing fuels like tall grasses and wood piles. And within 5 feet of the house, the goal is to stop the fire dead in its tracks, with things like rock beds and well-irrigated grass.

Cohen also came up with a long list of suggestions for preventing ember fires on the house itself, from the big and obvious ones, like replacing your flammable wood roof, to the smaller and less obvious, like making sure your garage door has a tight seal with the concrete and removing decorative juniper trees, which are extremely flammable.

Some of these ideas were pretty intuitive and had been floating around for a long time. In many fire-prone communities, homeowners had long been encouraged to clear flammable vegetation from their properties and to maintain their homes in ways that would reduce their chances of catching fire. But Cohen’s experiments allowed him to put hard numbers to people’s intuitions — and to develop specific, evidence-backed recommendations for the changes homeowners should make.

Cohen’s experiments also showed that when those changes were made, a house was much less likely to burn. In fact, he showed that was the main factor in whether a house was going to burn. It wasn’t about the intensity of the wildfire or its size — it was really about what was happening within 100 feet of your home.

All of this led him to a further, far more radical conclusion: it’s possible to not control extreme wildfire behavior, and yet still have houses survive.

In other words, if structures near fire-prone areas were designed and maintained to withstand fire, we might not need to fight some wildfires at all. If the only goal was to save houses, that ruled out fighting a lot of forest fires.

Cohen thought he had come up with a way to save houses and to let fires burn naturally — he thought it was a win-win. And so in 1999, he presented a paper about his findings at a fire conference in front of people from the Forest Service and state fire agencies. These were people who were in a position to change policies. But Cohen says they were totally uninterested. Cohen’s research implied that basically everything about how the Forest Service dealt with wildfires was wrong.

The 10 AM rule had left us with a huge fire fighting infrastructure, so the Forest Service was spending hundreds of millions of dollars on planes and fire crews, and was approving massive logging projects on the grounds that thinning out the forest would help reduce the intensity of wildfires and save homes. Cohen was saying: actually, it would be way more effective if you just encouraged homeowners to maintain and retrofit their properties.

“I believe that people taking more ownership in their home and having defensible space is number one,” says Shawna Legarza, the National Director of Fire and Aviation Management for the Forest Service. She says that, over her thirty year career in the Forest Service, she’s seen increasing emphasis placed on community preparedness and prevention. And she’s happy about that.

But she says there’s only so much the Forest Service can do to encourage people to make changes — a lot of that work falls to local governments and individual homeowners. And even today, not everyone is convinced that it’s important to invest in the kinds of preparations that Cohen recommends.

“Some communities don’t believe a fire will ever happen where they’re at… And unfortunately time is showing us that it does happen. Fire has no boundaries and no preference for where it burns.”

In the meantime, the Forest Service has a congressionally-mandated duty to fight forest fires.

Last year, the federal government spent more than 2 billion dollars fighting fires and just a small fraction of that on prevention and mitigation efforts. We continue to view fire as primarily an emergency response activity.

It’s hard to shift the culture — especially when there’s so much history behind the idea that we’ve got to do something about fire, whether it’s effective or not. We, the public, expect to see the dramatic shots of airplanes flying over raging fires, dropping water on them.

But when communities put the principles Cohen articulated into practice, they work. There are several communities in Southern California built with wildfires in mind that have survived when nearby homes didn’t. But those homes are mostly custom designs in gated communities, with homeowners associations that enforce strict rules about vegetation clearing and home design. Making changes elsewhere is more complicated — for starters, many homeowners may not even have 100 feet of space to clear and fireproof. It’s expensive to replace your roof. For renters, they may not have the authority to make changes to their homes. And in many cases, there aren’t incentives for people to invest.

Not to mention, many homeowners just kind of instinctively understand that the odds of being in a wildfire are extremely low. There are more than 40 million homes in wildfire-prone areas, and only a few thousand burn every year. Homeowners might decide it’s just not worth spending time and money to change their properties.

Cohen’s ideas have become more mainstream over time. Fire agencies like the Forest Service now talk a lot about defensible space and there’s more emphasis placed on homeowner responsibility. Jack also helped start the prominent organization FireWise, which promotes fire preparedness. Enormously destructive fires of the past few years have forced people to think about how to make their homes and properties more fire-resistant.

But with climate change, the fire season is only getting longer. And no one’s really talking about getting out of the fire fighting business.

The Forest Service is currently fighting several dozen fires across the western United States. When you’re that busy running around putting out fires — literally — it’s hard to focus on how to prevent them from being so destructive in the first place.

Cohen retired from the Forest Service a few years ago, feeling like all his research hasn’t made much of a difference in the end. When he’s watching the news — especially coverage of the past few destructive fire seasons in California — he’s noticed there isn’t a lot of talk about making homes more fire resistant or clearing more defensible space. Instead, there’s a lot of talk about firefighting.

The continued sense of fatalism frustrates Cohen — the feeling that if fire suppression can’t solve the problem, then nothing can be done. But as Jack says, “The bottom line is that we can do something. It just doesn’t have anything to do with controlling the wildfire.”