Wednesday, July 18, 2007

Angora Fire: Burning Homes, Not Crownfire, Fueled an Urban Conflagration

Within the next two weeks, the California State Fire Marshall will release a final Building Damage Assessment Report of the 3,100 acre Angora Fire located near Lake Tahoe. Initial newsmedia accounts stated that over 250 homes were destroyed. Nearly all of the damage or destruction to buildings occurred within the first few hours after the wildfire started as the wind-whipped blaze spread through the small community of Meyers, California. See the North Tree Fire website for an excellent Google Earth tour of the Angora Fire and spatial analysis of destroyed homes. A detailed description of the actual fire behavior of the Angora Fire, an analysis of the way that the fire spread through both residential areas and undeveloped wildlands, and the process by which individual structures were ignited and consumed by fire will hopefully be revealed in the Damage Assessment report.

While flames were still spreading and smoke was spewing during the first days of the wildfire, many claims were made in the press about the role that wildland vegetation, particularly trees, played in causing wildfire destruction of houses, and alternately, the role that Forest Service fuels reduction projects and fuelbreaks played in saving homes from wildfire destruction. Based on eyewitness accounts of folks who live in or have recently visited the Angora Fire area, the following is our assessment of the facts about the Angora Fire as we currently understand them:

Surface Fire, Not Crown Fire, Entered and Ignited the Residential Area

Contrary to prevailing beliefs that a tsunami-like towering inferno rolled across the community of Meyers, in actuality, the headfire (the fastest-spreading and hottest part of a wildfire’s flame front) initially bypassed the community. A shift in wind direction then enhanced the flanks of the wildfire perimeter to spread into the residential area. At the places where the wildfire moved from undeveloped wildlands into the developed neighborhoods, with little exception the wildfire was a surface fire, not a crown fire.

This point is worth repeating: the Angora Fire was burning on the ground surface, not the tree tops, when it entered the residential area. Pro-logging interests are currently using the Angora Fire to argue that the lack of logging around Lake Tahoe communities created hazardous fuel conditions that allowed a crownfire to destroy those homes. The reality is that burning homes ignited surrounding tree tops and adjacent homes. Although there were a few instances when the tree canopies did not ignite even though nearby homes had burned, there were no instances where burning canopies alone minus burning structures had ignited other homes.

Fuels Reduction Treatments Did Not Stop the Wildfire

Also contrary to prevailing beliefs that fuels reduction treatments stop wildfire spread, the Angora Fire spread through areas that the Forest Service had completed fuels reduction projects within the last six years--in some places, fuels treatments had been completed as recently as three months ago.

This point, too, cannot be overstated: where the Angora Fire entered into the residential area, the wildfire had spread through a fuels treatment unit. Fuels treatments alone do not stop wildfire spread or protect communities from home ignitions.

The bottom line is that there are numerous tradeoffs involved in constructing and maintaining fuels reduction treatments. Depending on the amount and kind of tree thinning conducted, fireline intensity and the risk of crownfire may decrease, but the rate of surface fire spread may actually increase. The rate of spread is a critical factor in determining the number of homes that are simultaneously exposed to flames and the ability of firefighters to construct containment lines. Simply reducing the amount of trees or shrubs alone does not guarantee better wildfire protection for adjacent communities.

Recent statements to the media have acknowledged that under extreme fire weather conditions, fire suppression has limited success even with fuels treatments. But fire suppression has successfully contained 97-99% of all wildfires during initial attack during the last decade regardless of fuel loads. The 1-3% of the wildfires that defy successful containment typically occur during severe fire weather or extreme fire behavior conditions, and it is under these conditions that most Wildland/Urban Interface fire disasters occur. Thus, if fuels reduction treatments do not benefit suppression efforts during these extreme conditions, then they cannot provide protection for vulnerable homes, as evidenced on the Angora Fire. There may be other social or ecological benefits to reducing fuels in forested wildlands, but protecting homes during severe fire weather or extreme fire behavior conditions is not one of them, and they ought not to be “sold” to the public as being designed for community wildfire protection.

Untreated Thinning Slash Does Not Make for a "Completed" Fuel Treatment

Forest Service officials were quick to claim that recently completed fuels treatments prevented the wildfire from entering the tree canopies, and spared as many as 500 more homes from wildfire destruction. However, regardless of the fire behavior within fuels reduction units, there is a lingering question as to whether or not slash treatments had been fully completed inside the units. The Forest Service annually reports to Congress on the number of acres it has completed fuels reduction, and counts as “acres treated” units where it conducts a tree thinning operation, and then can count those same “acres treated” again when it finally treats the thinning slash, normally a year or more after the initial tree cutting. Thus, for a given 40 acre unit, the agency can report 80 acres of fuels reduction treatments “completed” by adding the tree cutting and slash burning treatment acres together.

Within some of the fuel treatment sections located near residential areas there remained large unburned slash piles mountainously high. Logging slash in general poses extreme fuel hazards that can create high fire intensity and loft embers that can ignite spotfires ahead of the flame front. It is unknown at this time what role if any the untreated slashpiles inside fuels reduction areas may have played in the spread or severity of the Angora Fire. Trees inside the fuels reduction units have been severely scorched and have browned canopies even though the crowns were not consumed. Heat generated from excessive surface fuels like logging slash is sometimes sufficient to kill large trees by "heat girdling" their trunks, baking their roots, or convectional heat cooking the canopy even though flames do not get anywhere near the tree tops.

A Wildland Fire Became an Urban Conflagration

Once the Angora Fire spread out of the fuels treatment units into the first line of houses along the outer edge of the residential area, it rapidly transitioned from a wildland fire to an urban conflagration. The residential portion of the Angora Fire spread as a chain reaction of burning homes igniting adjacent homes. The intense, prolonged heat output from flaming structures sent a sustained flow of radiant heat and burning embers that ignited vegetation and other homes located downwind. This intense heat output enhanced firebrand ignitions of homes and surrounding vegetation across paved streets that progressed downwind igniting houses from block to block.

The first homes to burn occurred barely one hour after the wildfire was first detected, but once this first line of homes ignited, the fire dramatically increased intensity so that many homes were simultaneously set aflame within a short time. Tragically, it appears that even homes that had prepared for wildfire by having flame-resistant roofs and defensible space were consumed by the flames spread from homes that had not taken these steps.

Observing the effects of the Angora Fire, it appears that the residential fire dynamics operated almost independently of the fire burning through the undeveloped wildland areas. While it is true that vegetation was much denser in the residential area than in the surrounding wildland, the principal fuel causing extreme fire intensities were burning structures rather than vegetation, although both fuel types were involved in the conflagration. There were hundreds of undeveloped lots interspersed within homes but the wildfire did not move through these densely-vegetated lots with the same intensity as it did through highly-developed residential areas. And again, in many cases burning homes ignited surrounding tree canopies, but in no case did crownfire without structural fire ignite homes. The final Damage Assessment report will hopefully provide more details on the actual fire behavior and effects of the Angora Fire.

Preventing Future Wildfire Disasters Means Reducing Home Ignitability

For policymakers trying to make sense of the Angora Fire and take steps to prevent similar future disasters, there are a number of important lessons to be learned. First, it is time to stop speaking in vague generalities about the spatially amorphous “Wildland/Urban Interface Zone,” and instead, focus attention on what Forest Service fire researcher Jack Cohen calls the Home Ignition Zone. Too often, when policymakers speak about the Wildland/Urban Interface Zone, they focus on the (publicly-owned) wildland part and tend to ignore the (privately-owned) urban portion of the problem. Management actions to reduce home losses to wildfire must be centered on reducing fuel hazards in the home ignition zone, an area 200 feet or less in radius around structures. Vegetation growing within developed suburban areas should not be considered “wildland” but rather residential vegetation, and it is the residential vegetation located within the home ignition zone that matters most in terms of reducing hazard potential. Where home ignition zones overlap, community cooperation will be necessary to reduce everyone’s vulnerability to igntion.

Second, it is time to stop thinking about creating defensible space around homes as a responsibility solely of individual homeowners. Instead, this is rightfully a social problem and a community-wide responsibility. Rugged individualism is not a viable strategy for protecting one’s home that is most threatened by ignitions coming from a neighbor’s property. Not everyone who lives in rural America has the wealth or legal or physical ability to deal with fuel hazards of their homes. There are lots of impoverished people, renters who do not own the homes they live in, and elderly or infirmed people who cannot do the necessary work themselves. In these cases, it is appropriate for governments and communities to facilitate hazard reduction work on these properties. A socially progressive policy to reduce home losses to wildfire would devise a set of grants, low-interest loans, and free labor sources like Americorps to get the work done for people who need assistance.

Ultimately, though, it is time for our aesthetic sensibilities to adapt to the fire-prone environments we live in. It is time for homes to be located, designed, built, and maintained so that they can survive the spread of wildland fires with minimal or no need for human intervention. Wildland fires are inevitable; consequently, wildfires during extreme fire behavior conditions are inevitable as well. The current strategy of protecting homes through attempts to prevent and/or suppress wildfires is simply not a viable strategy, especially given the fact that most ecosystems in North America are adapted to or dependent upon recurring fires to maintain their ecological integrity and biological diversity. Added to this is the fact that global warming and climate change will likely increase the frequency of large-scale high-intensity wildland fires that will simply overwhelm the capacity of the fire services to successfully fight every wildfire.

The FUSEE vision is to recreate fire-compatible communities capable of living safely and sustainably within fire-permeable landscapes and fire-adapted ecosystems. May the Angora Fire provide us all with a teachable moment to change public policies and personal lifestyles needed to move toward that vision.

--FUSEE Staff

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