 Today, more and more people are leaving the city to enjoy the beauty and tranquility that nature offers. Homes and communities are springing up where once only trees and fields stood. While living next to wildlands may offer serenity, it also poses great risk. A wildland environment is a fire environment. Fire in wildland urban areas is inevitable. It's part and parcel of the natural order of things. But that doesn't mean we are helpless in the face of the flames. We may not be able to stop wildland fires from occurring, but we do have a choice about whether or not our homes will survive a wildfire. And the steps we need to take to protect our homes are actually surprisingly simple. What ignited this house and burned it down were the little things. For nearly three decades, Jack Cohen, a fire research scientist with the USDA Forest Service, has studied the physics of wildfire in order to understand how fire behaves. And in doing so, he has helped dispel many myths that cloud our understanding of fire and inhibit our ability to protect ourselves. The big problem with our perception of fire in general in our society is that, first of all, we as civilians, as homeowners, can't do anything or don't do anything about fire. Over the last roughly thirty years, I've had that challenged and over the last ten years I've pretty much come to the perception that there are definitely choices that we've got to avoid residential fire disasters during wildfires. Most people believe wildfire to be a tsunami-like force sweeping across the countryside, destroying everything in its path, a perception regularly reinforced in the media. The firestorm rages on across the in-the-northwest tonight. The wind and dry conditions stack the chips in the fire's favor. But as Jack and other researchers studied fire, they began to see fire in a different light, not simply as a wave moving along a single path. I was seeing things during fires that I just sort of filed away in the back of my head, things that didn't quite match what my expectations were. So for example, when I was just a student, I watched a film about a fire in Southern California and my mental model when I started out watching this film was, well, the wildland fire would come up and get the edge of the community and it would burn those houses down. And yet when I was watching this film, it wasn't just the houses on the edge that were totally destroyed. It was also several blocks inside the community where the houses were destroyed. If fire proceeded as a wave, why then did homes outside the path of the wildfire burn down? And in other fires, why did some homes, directly in the path of the fire, survive while neighboring houses burn to the ground? Researchers like Jack believed that if they could explain these inconsistencies, they could better understand how wildfire destroyed homes. To do this, they conducted laboratory and field experiments and post-fire investigations. When I started on this problem of houses burning during wildfires, I started really paying attention to not only the things that were destroyed during a wildland urban interface fire event, but also maybe especially those things that survived. In investigations like this one in the bitter root of Montana, Jack tries to reconstruct the fire's path to the home. He also challenges the assumption that crown fires, large flames burning in the tree canopy, destroyed the homes. When I get to a site of residential destruction, I try to get a sense of the pattern of the exposure. We can begin to also trace a chronology, a timing. For example, on the glider we can see where there was wilt around the glider and yet under the glider there was no burning from the crown fire and yet we can also see where the glider was burning from the house. And what that tells us is that the crown fire was long gone by the time this house was burning. I start challenging the idea that the big flames burned this house down. I particularly look for the degree of heating between what was the crown fire and what was the house. And one of the things that I noticed was the foam hand grips. They would have been dripping off. They would have totally been melted away. And these are highly vulnerable to high intensity heat. Postmortems like this one led to a breakthrough in sight. What my investigations are telling me is that more than half the time the big crown fires aren't igniting these structures. It's something else. It's the little things. If crown fires didn't ignite these structures, then why and how did these homes burn? In the effort to solve this mystery, researchers applied what they already knew about fire behavior. Fire spreads from ignition to ignition. Fire doesn't spread by some magical whim. It doesn't spread like an avalanche or a flash flood or a lava flow, something on that order. It spreads according to meeting the requirements for combustion. If homes burn as the result of a chemical reaction called combustion, then the entire process can be broken down and studied scientifically. There are three basic ingredients necessary to create combustion. Oxygen, heat, and fuel. Remove any one of these elements and the fire cannot continue. Scientific research determined that home ignitions are caused by flames and by firebrands. Flames directly transfer enough heat to ignite the home. This transference of heat can occur by thermal radiation when a fire conveys enough heat to nearby fuel so that the fuel combusts. Or it can be caused by convection when fire comes into direct contact with the fuel. Homes can also be ignited by firebrands, burning embers that fly through the air, land on combustible materials, and directly ignite them. Scientists also investigated the relationship between time and fire and dispelled another widely held misconception. When we watch a fire spreading through the forest, it may last for hours and hours, but it doesn't last hours and hours at a particular location with those big flames. It is the twigs, needles, grasses, and other fine fuels that allow forest fires to burn, but it doesn't take long for that material to be consumed. It's not that the big flames don't provide a lot of heat, it's just that they don't provide that heat over a very long time. So, for example, the big flames come up in some proximity to a house with wood walls, and we find that, yeah, it's really intense and certainly intense enough to cause human injury, but over the period of time that they last on the order of 60 seconds, it's not sufficient to ignite that wall. We assume that a fire which burns humans quickly can also ignite wood quickly, but our intuitions are misleading. Humans are far more susceptible to injury from heat exposure. Because most crown fires consume their fuel in a given area in about a minute, they simply burn out before they can ignite most homes or structures. Other experiments revealed an equally surprising finding about fire and distance. Crown fires, even intense crown fires that burn at a distance greater than 100 feet, cannot provide enough radiant heat to ignite a structure. It gives us an opportunity to change where that fire goes by somehow changing the situation so that it doesn't meet the requirements for combustion. Armed with this information, Jack formulated the home ignition zone. The home ignition zone is an area that includes the home and its immediate surroundings, which, if properly conditioned, can save the home during a wildfire. The home ignition zone regards property from the perspective of a wildland fire. A house is no longer a home, it is potential fuel, and everything surrounding this fuel is a potential heat source that could ignite it. The home ignition zone determines the vulnerability of our home to wildfire, and that home ignition zone extends out a couple of hundred feet at most from the house. Protecting a home begins by reducing the flammability of the home itself and the surrounding property. For example, by switching to flame-resistant roof materials. Thinning out trees can stop crown fires from spreading from canopy to canopy until it reaches the home. And clearing the zone of dry vegetation and flammable objects can eliminate heat sources that might form a path to the home. The object is not to entirely eliminate fire within the zone, but to ensure that fires that do start can't burn long enough or intensely enough to ignite other objects. The goal is simple, reduce the fuel, and the fire cannot continue. This property is a good example of how there is plenty of clearance on this property. From the irrigated lawn, it's essentially fire-free. It won't propagate the fire, it won't spread the fire. The surrounding landscaping is separated from the rest of the forest, and there's a mixed wood. So in this particular case, it's got plenty of clearance. The real issue on this house was the wood roof that they've changed out. The wood roof would have dominated the likelihood for ignition on this house. Reducing combustible vegetation adjacent to the home also helps to reduce the potential for a fire involving the house. Well here we have an example of a home ignition zone that has a considerable amount of space between the house and the dense forest beyond. The home, as well as its surroundings, is part of the home ignition zone. And so the noncombustible walls and the noncombustible roof have very low ignition. Every potential heat source in the zone must be evaluated, even a neighbor's home. If multiple homes share ignition zones, then each home becomes a potential heat source that could ignite the other homes. Solving this problem becomes a shared concern requiring cooperation and planning. The home ignition zone empowers people and neighborhoods to take relatively simple steps to save their homes and communities, even from the most intense blazes. Perhaps the greatest vulnerability in the home ignition zone is the threat posed by firebrands. Jack was first introduced to the importance of firebrands igniting homes in 1977 as a young research scientist in Paddy Canyon, Montana. Initially we could begin to see just a little bit of flame over this ridge and at the same time could see some of the firebrand ignitions, those spot ignitions from the burning embers that were coming out of this fire beginning to ignite on this hillside. The intense heat of a fire on the ridge generated swirling winds that carried and dropped burning embers on homes far in advance of the flames. We were right here on this road, so we were fairly close to this crown fire, a couple of hundred feet from this crown fire, and yet the radiation wasn't so intense to where it would have ignited the wood walls because we're more vulnerable to the heat than what wood walls are, but there was this tremendous blizzard of burning embers coming out of this intense fire. Severe wildfires commonly generate firebrand blizzards. Like the Paddy Canyon fire, these blazes quickly race out of control. Firebrands are swept along fast-moving currents and deposited onto homes ahead of the fire, causing them to burn to the ground even though the crown fire never came near them. Because firebrands are so small, we tend to ignore them and instead focus on the large flames. Ironically, we tend to pay a lot of attention to the flames that can be relatively close to the home and not ignite it and ignore those things that don't bother us very much. They're highly inconvenient if you're caught in an ember blizzard, having these embers on the back of your neck or burning small holes in your clothes is obviously not a great experience, but it's not mortally threatening to us and yet this blizzard of firebrands can, just like snow, begin to collect and pile up in certain locations around the house. Our intuitions belie the truth. A tiny firebrand can be more devastating than a raging crown fire, but that doesn't mean that homeowners are helpless. If we consider a house as fuel and reduce the flammability of materials on and near it, we can protect against firebrands igniting our home. Vigilance begins with the roof, the most vulnerable part of the home to firebrands. The most flammable roofs, not surprisingly, are constructed of wooden shingles. Firebrands that land on or between the shingles can easily ignite the structure. To find safer, less flammable materials, Jack has conducted experiments on composition shingle roofs. What I did was to pile pine needles, actually a lot of us gathered pine needles and put them on the roof to a depth of about an inch and a half, and then we ignited it to demonstrate that the roof wouldn't ignite. It's somewhat dramatic to watch a surface fire spreading across a roof. It tends to be counterintuitive to our expectations, but you find that composition shingles just don't carry fire. Experiments have also been conducted on siding and deck materials. I'm looking at materials, for example, exterior plywood, wall siding, and wood decking that always ignite from the firebrands that I deposit on the deck, and then I look at other materials to see how they compare with regard to ignitions. Initial results have determined that fiber cement siding has proven to be non-flammable. Still, other areas around a home are vulnerable to catching fire. Any gaps or cracks in a structure or any place where combustible materials or firebrands can gather are ideal for sustaining ignitions. By conditioning the home ignition zone, we can prevent wildland urban fire disaster. It's been proven. When fires broke out in Bel Air, California in 1961, 95% of all homes with non-flammable roofs and a 30 to 50 foot buffer from fire survived. The 1990 Painted Cave fires in Santa Barbara, California experienced similar results. There, 86% of homes with non-flammable roofs and 30 foot separation from flames survived while other homes burned. Scientists like Jack Cohen have dramatically changed our understanding of wildfire. We now better understand how homes ignite and we possess the remedies to save our homes. But that raises a question. Why should people take responsibility for their property? Isn't that the job of firefighters? We can't rely on fire agencies to either keep the fire away or to keep our house from igniting. The wildland firefighters job is to contain the wildfire. They go out and they remove vegetation to keep the fire from spreading and thereby we contain the fire that way. Wildfires can quickly become so overwhelming that firefighters are unable to protect individual homes so the burden must fall elsewhere. When we think about how homes ignite during wildfires and realize that it's the home ignition zone that determines the vulnerability of our home and that by and large we own that and that we're the only ones that can do something, that means that we are going to have to participate in this problem as homeowners. The good news is that home survival isn't an all or nothing proposition. We don't have to completely rebuild our homes or re-landscape our yards. The goal is to minimize ignitions during a wildfire in order to contain the fire. Preparation, however, must begin long before smoke appears on the horizon. We've got to do things before the fire ignites. Those things like seasonal cleanup of needles around our house, changing the roof, thinning out the forest that's next to our house. Those are the kinds of things that we can't do when the threat becomes imminent. Saving homes demands a fundamental change in our way of thinking. To coexist peacefully with nature, we must learn to be compatible with wildfire. We must realize that wildfire is inevitable in nature, but that destruction of our property is avoidable. We can save our homes. It's up to us.