Burned homes in Slave Lake. May 16, 2011. Alberta, Canada. CTV.
Researchers have found that building codes based on lessons learned during the deadly 1991 Tunnel Fire in the Oakland Hills of California can reduce the vulnerability of homes to wildfires.
In a paper titled Mandatory vs. voluntary adaptation to natural disasters: the case of U.S. Wildfires, authors Patrick W. Baylis and Judson Boomhower describe how they scoured property and wildfire records to identify which homes were constructed under building codes requiring enhanced resistance to wildfires.
Chapter 7A of the California Building Code which went into effect in 2008 requires certain fire resistance measures, including exterior construction materials used for roof coverings, vents, exterior walls, and decks. It applies to new construction of residential and commercial buildings in designated fire hazard severity zones.
The researchers discovered that a 2008 or newer home is about 16 percentage points (40%) less likely to be destroyed than a 1990 home experiencing an identical wildfire exposure. There is strong evidence, they concluded, that these effects are due to state and local building code changes – first after the deadly 1991 Oakland Firestorm, and again with the strengthening of wildfire codes in 2008. The observed vintage effects are highly nonlinear, appearing immediately for homes built after building code changes. There are no similar effects in areas of California not subject to these codes or in other states that lack wildfire codes.
Their findings are similar to those in a paper published October 4, 2021 in which researchers analyzed the structures that were destroyed and those that survived the Camp Fire that ran through the city of Paradise, California in 2018. They considered at least four primary characteristics of structures:
Were they built before or after the adoption in 2008 of Chapter 7A of the California Building Code.
Distance to nearest destroyed structure.
Number of structures destroyed within 100 meters.
Pre-fire overstory tree canopy within 100 meters
They found that the last three criteria were the strongest predictors of survival. Homes more than 18 meters (59 feet) from a destroyed structure and with less than 53 percent pre-fire overstory canopy within 30 to 100 meters (98 to 328 feet) survived at a substantially higher rate than homes in closer proximity to a destroyed structure or in areas with higher pre-fire overstory canopy. Most fire damage to surviving homes appeared to result from radiant heat from nearby burning structures or flame impingement from the ignition of near-home combustible materials. The researchers concluded that building and vegetation modifications are possible that would substantially improve outcomes. Among those include improvements to windows and siding in closest proximity to neighboring structures, treatment of wildland fuels, and eliminating near-home combustibles, especially within 1.5 meters of the structure.
(The video below was shot December 31, 2021, the day after the Marshall Fire destroyed more than 1,000 homes in Boulder County, Colorado. Notice that most of the surviving homes seen in the video had fewer homes in close proximity.)
The authors noted that while Chapter 7a includes requirements not found in many building codes, a few other codes are more complete incorporating multiple construction classes based on anticipated radiant heat, flame, and ember exposure levels. For example Chapter 7A does not consider the interaction between components such as siding, window, and the under-eave area on an exterior wall.
California is embarking on a pilot project in which owners of vulnerable homes in lower income neighborhoods will be given grants up to $40,000 to retrofit the structures, making them more resistant to wildfires.
The state of California is beginning the initiative in rural San Diego County
Relatively fire-resistant homes can ignite during low-intensity wildfires if a path of combustible material, such as fences, stairs, decks, or support beams lead the fire to the home. Image from Texas Forest Service report about fires in 2011.
Recognizing that the Home Ignition Zone can be the most important factor that determines how vulnerable a residence is to an approaching wildfire, the State of California has embarked on a pilot program that will grant up to $40,000 to homeowners who retrofit their homes to make them more fire resistant.
Working with the Federal Emergency Management Agency (FEMA) the funds in the $100-million project will be available in areas that are commonly threatened by fires.
The California Department of Forestry and Fire Protection, or CAL FIRE, chose the communities of Dulzura, Potrero and Campo based largely on their concentration of low-income residents living in older, fire-prone homes. The state is also starting to roll out the pilot in Shasta County [in Northern California]. Residents with higher incomes can still qualify for the retrofits as long as they pay for a percentage of the work on a sliding scale.
There may be additional federal funds becoming available in the future. During a January 21 speech at Del Rosa Fire Station on the San Bernardino National Forest Vice President Kamala Harris spoke about wildland fires and the resilience of communities threatened by fire.
“We are talking with home owners and reaching out to communities,” she said, “to figure out how we can support them to create a community that is less likely to be so significantly damaged if a fire should hit.”
However, she may have been referring to the $100-million from FEMA and California.
Our take
We will never be able to prevent all fires that threaten homes and private property. We have to learn to Live With Fire. The Home Ignition Zone should be an extremely high priority in preventing structures from burning in wildfires.
Grants for homeowners to retrofit homes to make them more fire resistant is the right thing to do. These could be expanded to include modifying the vegetation within 100 feet of the structures. Below is an excerpt from an article posted September 24, 2020 on Wildfire Today:
“Ignition resistant homes, and collectively communities, can be readily created by eliminating and reducing ignition vulnerabilities within the Home Ignition Zone,” said Jack Cohen, a retired U.S. Forest Service Research fire scientist. “This enables the prevention of wildland-urban fire disasters without necessarily controlling extreme wildfires. Ironically, ignition resistant homes and communities can facilitate appropriate ecological fire management using prescribed burning. The potential destruction of homes from escaped prescribed burns is arguably a principal obstacle for restoring fire as an appropriate ecological factor. Therefore, it is unlikely that ecologically significant prescribed burning at landscape scales will occur without ignition resistant homes and communities.”
Here are some suggestions that could be considered for funding along with an enhanced prescribed fire program.
Provide grants to homeowners that are in areas with high risk from wildland fires. Pay a portion of the costs of improvements or retrofits to structures and the nearby vegetation to make the property more fire resistant. This could include the cost of removing some of the trees in order to have the crowns at least 18 feet apart if they are within 30 feet of the structures — many homeowners can’t afford the cost of complete tree removal.
Cities and counties could establish systems and procedures for property owners to easily dispose of the vegetation and debris they remove.
Hire crews that can physically help property owners reduce the fuels near their homes when it would be difficult for them to do it themselves.
Provide grants to cities and counties to improve evacuation capability and planning, to create community safety zones for sheltering as a fire approaches, and to build or improve resilient emergency water supplies to be used by firefighters.
At Del Rosa fire station in Southern California the VP was introduced by a wildland firefighter
Vice President Kamala Harris at the San Bernardino National Forest, January 21, 2022.
On Friday Vice President Kamala Harris traveled to California where she spoke about wildland fires and the fact that federal firefighters are “underpaid given the nature and value of their work.”
Her 12-minute speech was made at Del Rosa fire station on the San Bernardino National Forest as she stood in front of US Forest Service fire apparatus, Engine 330 and a Del Rosa Interagency Hotshot crew buggy.
“On behalf of the President and myself I want to thank all the men and women who serve in such difficult times but always with such grace. Thank you Sarah and thank you Chief,” the Vice President said as she began her remarks. Sarah Hudson, a firefighter, introduced the VP. More about that below.
Later the Vice President mentioned the pay of federal wildland firefighters.
“There will be $5 billion, and more actually,” she said, “for wildfire preparedness and resilience, and it will include, and this requires its own conversation, a pay raise for our federal firefighters. And I invite everyone to become familiar with the history of this issue and for how long they have been underpaid given the nature and value of their work, and so we are very, very excited to acknowledge their work not only in words but with the pay that recognizes the value of the skill and the dignity of the work that they perform…And I am very proud of the folks who in particular are on the ground doing this work every day. As I have said before I will say again, you inspire us all.”
The Vice President spoke for 12 minutes about wildland fire and reducing their impact, and never mentioned raking the forest.
She also covered the resilience of communities threatened by fire.
“We are talking with home owners and reaching out to communities,” she said, “to figure out how we can support them to create a community that is less likely to be so significantly damaged if a fire should hit.”
The Home Ignition Zone should be an extremely high priority in preventing structures from burning as a wildfire approaches.
“Surprisingly, research has shown that home ignitions during extreme wildfires result from conditions local to a home,” wrote retired US Forest Service Research scientist Jack Cohen in a 2020 article on Wildfire Today. “A home’s ignition vulnerabilities in relation to nearby burning materials within 100 feet principally determine home ignitions. This area of a home and its immediate surroundings is called the home ignition zone (HIZ). Typically, lofted burning embers initiate ignitions within the HIZ – to homes directly and nearby flammables leading to homes.”
Other speakers at the event included Secretary of Agriculture Tom Vilsack, California Governor Gavin Newsom, and Chief of the Forest Service Randy Moore.
Sarah Hudson, a US Forest Service firefighter with Heaps Peak Helitack, introduces Vice President Kamala Harris, January 21, 2022.
In addition to the dignitaries peaking at the event, Sarah Hudson, a senior firefighter on the Heaps Peak helitack crew on the San Bernardino National Forest made remarks and then introduced the Vice President. This may be the first time a wildland firefighter has performed such a feat. In her spare time Ms. Hudson serves in the California National Guard as a senior airman with the 163rd Attack Wing where she performs maintenance on ground support equipment for remotely piloted aircraft such as the MQ-9 Reaper. On several occasions a National Guard Reaper or similar National Guard drone have assisted firefighters by gathering real time imagery over ongoing wildfires in California.
The entire 35-minute event is covered in the video below.
Early Friday morning, about 20 hours after the Marshall Fire ignited, a drone operated by Twitter user WxChasing/Brandon Clement flew over subdivisions that were devastated by the December 30 fire. It found block after block of ash piles, some still smoldering. In many scenes there was scarcely a structure still standing. (Scroll down to see the video.)
All of the reasons why some houses did not burn even though dozens around them were consumed could not be determined from the video, but there was one common feature — the survivors were more distant from the neighboring homes. Many houses in the subdivisions were only 10 to 20 feet apart based on archived imagery in Google Earth.
The fire was driven by very strong winds gusting at 60 to 100 mph, extremely dry conditions after months of drought, and relative humidity in the mid-20s. These are the very worst fire conditions. The weather paired with the nearly back to back structures led to the fire spreading through a continuous human-made fuel bed. When one house burned the convective and radiant heat easily ignited its neighbor, which ignited its neighbor, etc.
The fire in the vegetation and structures lofted burning materials far downwind, creating distant spot fires in the home ignition zone on bone dry lawns, mulch beds around ornamental plants, and on structures. It is unknown at this point how many had been designed and built to be fire resistant, such as the characteristics of the roof, vents, siding, doors, windows, foundation, fences, eaves, and decks. A FEMA publication (13 MB) has excellent detailed recommendations. Headwaters Economics found that the cost of building a fire-resistant home is about the same as a standard home. Local building codes could regulate these features. But if the lot size is so small that residences are only 10 to 20 feet apart, if one becomes fully involved, the neighbors also burn, especially during windy conditions.
So far we have listed some factors that affect the vulnerably of structures during a wildland-urban interface fire: home spacing and lot size, the envelope of the structure itself, fire codes, and the home ignition zone. Others are:
Safety zones where residents can shelter in place;
Road and driveway width, wide enough for large fire trucks;
Turnarounds at the end of roads;
Signage, and;
Emergency water supply.
The video below of the Marshall Fire devastation was shot by WxChasing/Brandon Clement at first light on December 31, 2021, the day after the fire started. Not long after, snow began falling. The National Weather Service in nearby Boulder recorded an accumulation of eight inches.
The blaze in Northern California destroyed 18,804 structures, most of which were in Paradise
Aerial image showing a portion of Magalia just NW of Paradise, illustrating a gradient of fire damage to overstory vegetation with distance from destroyed homes. At least in some areas, burning homes may have influenced the effects to overstory vegetation more so than burning overstory vegetation influenced the outcome to homes. Photo: Owen Bettis, Deer Creek Resources.
In a paper published October 4, 2021, researchers analyzed the structures that were destroyed and those that survived the Camp Fire that ran through the city of Paradise, California in 2018. They considered at least four primary characteristics of structures:
Were they built before or after the adoption in 2008 of Chapter 7A of the California Building Code which requires certain fire resistance measures, including exterior construction materials used for roof coverings, vents, exterior walls, and decks and applies to new construction of residential and commercial buildings in designated fire hazard severity zones.
Distance to nearest destroyed structure.
Number of structures destroyed within 100 meters.
Pre-fire overstory tree canopy within 100 meters
They found that the last three criteria were the strongest predictors of survival. Homes more than 18 meters from a destroyed structure and with less than 53 percent pre-fire overstory canopy within 30 to 100 meters survived at a substantially higher rate than homes in closer proximity to a destroyed structure or in areas with higher pre-fire overstory canopy. Most fire damage to surviving homes appeared to result from radiant heat from nearby burning structures or flame impingement from the ignition of near-home combustible materials. The researchers concluded that building and vegetation modifications are possible that would substantially improve outcomes. Among those include improvements to windows and siding in closest proximity to neighboring structures, treatment of wildland fuels, and eliminating near-home combustibles, especially within 1.5 meters of the structure.
The authors noted that while 7a includes requirements not found in many building codes, a few others are more complete incorporating multiple construction classes based on anticipated radiant heat, flame, and ember exposure levels. For example Chapter 7A does not consider the interaction between components such as siding, window, and the under-eave area on an exterior wall.
There is an opportunity for much needed improvement in both current building codes and how we live in wildfire prone WUI areas.
Below is the complete Conclusion section from the research.
Conclusions
The results of this study support the idea that both proximities to neighboring burning structures and surrounding vegetation influence home survival with wildfire. Denser developments, built to the highest standards, may protect subdivisions against direct flame impingement of a vegetation fire, but density becomes a detriment once buildings ignite and burn.
Recent examples of losses in areas of higher density housing include the wind-driven 2017 Tubbs Fire in northern California, where house-to-house spread resulted in the loss of over 1400 homes in the Coffey Park neighborhood (Keeley and Syphard 2019), and the wind-driven 2020 Almeda Fire in southern Oregon, which destroyed nearly 2800 structures, many in denser areas in the towns of Talent and Phoenix (Cohen and Strohmaier 2020). Once fire becomes an urban conflagration, proximity to nearby burned structures becomes especially important because occupied structures contain significant quantities of fuel, produce substantial heat when burned, and are a source of additional embers. For density to be protective, home and other structure ignitions would need to be rare.
Fifty-six percent of homes in Paradise built during or after 2008 did not survive, illustrating that much improvement is needed in both current building codes and how we live in wildfire prone WUI areas before proximity to nearby structures becomes a benefit rather than a vulnerability. The threat posed by nearby burning structures as well as our finding of an apparent strong influence of vegetation 30–100 m from the home—a distance that in most cases encompasses multiple adjacent properties—demonstrates that neighbors need to work together to improve the overall ability of homes and communities to resist wildfire exposures.
To maximize survivability, homes need to be designed and maintained to minimize the chance of a direct flame contact, resist ember ignition, and survive extended radiant heat exposure. Our analyses demonstrating the strong influence of nearby burning structures on home survival suggests improvements to resist radiant heat exposures may be warranted in the California Building Code—i.e., increasing the standards for buildings within a certain minimum distance of other structures.
Some possible improvements might include noncombustible siding with rating minimums tied to proximity to other structures, both panes in windows consisting of tempered glass, or installation of deployable non-combustible shutter systems. Additionally, certain options for complying with Chapter 7A are better for resisting radiant heat and flame contact exposures and could minimize fire spread to other components. Whereas the International Code Council’s Wildland Urban Interface Building Code (International Code Council 2017) provides three ignition-resistant construction classes to allow for material restrictions as a function of exposure level, Chapter 7A consists of one level, so is binary in nature in that a building either needs to comply, or it does not. The Australian building code for construction in bushfire prone areas, AS 3959 (Standards Australia 2018), incorporates six different construction classes based on anticipated radiant heat, flame, and ember exposure levels. Interaction between components, for example, siding, window, and the under-eave area on an exterior wall, is not considered.
Our summary of damaged but not destroyed homes in Paradise was in line with other reports showing a high proportion of home ignitions indirectly resulting from embers (Mell et al. 2010). Embers frequently ignited near home combustibles such as woody mulch, fences, and receptive vegetative fuels with flames and/or associated radiant heat then impacting the home itself, supporting awareness of the importance of combustibles within the first 1.5 m (5 ft) of the building on home survival.
A re-interpretation of defensible space fuel modifications is needed to increase the building’s resistance and exposure to embers and direct flame contact, especially in the area immediately around a building and under any attached deck or steps. This does not diminish the value of defensible space fuel modifications 9 to 30 m (30 to 100 ft) away from the home, which not only reduces fuel continuity and the probability of direct flame contact to the home, but also provides firefighters a chance to intervene.
While our data show a relationship between home loss and vegetative fuels (high pre-fire overstory canopy cover likely associated with a greater litter and woody fuel abundance, as well as other wildland understory vegetation) that can contribute to fire intensity and ember generation, the WUI fire loss issue has been described as home ignition problem more so than a wildland fire problem (Cohen 2000; Calkin et al. 2014). The damaged home data were in line with this view, with few homes showing evidence of continuity with wildland fuels that would contribute to flame impingement, but numerous homes with near home fuels, both from manmade and natural sources, that led to direct or indirect ember ignitions.
California’s Mediterranean climate will continue to challenge its residents with regular wildfire exposure throughout the state. Whether through modifying the nearby surface and vegetative wildland fuels or the home itself, adapting to wildfire will take time. The good news is that the trend in survival is improving with newer construction practices. However, with 56% of houses built after 2008 still succumbing to the Camp Fire, much room for improvement remains.
Our data suggest it is possible to build (and maintain) buildings that have a high probability of surviving a worst-case scenario type of wildfire, even in fire-prone landscapes such as the Paradise area. Newer homes built after 1972, where the nearest burning structure was >18 m away, and fuels associated with vegetation 30–100 m from the home kept at moderate and lower levels (<53% canopy cover) had a 61% survival rate—an approximately 5-fold improvement over the Paradise housing population as a whole. Survival percentages substantially higher still are potentially possible if all components of risk, including ember generation in nearby wildland fuels, continuity of wildland and other fuels on the property, and home ignitability are sufficiently mitigated.
Citation:
Knapp, E.E., Valachovic, Y.S., Quarles, S.L. et al. Housing arrangement and vegetation factors associated with single-family home survival in the 2018 Camp Fire, California. fire ecol 17, 25 (2021). https://doi.org/10.1186/s42408-021-00117-0
Victoria Prescribed Fire, Black Hills National Forest. South Dakota. USFS photo by Matt Daigle. March, 2021.
In recent weeks there have been discussions online about whether or not fuel reduction projects can aid firefighters by reducing the intensity of wildfires. These rumblings are heard from agenda driven advocacy groups including the John Muir Project.
There is no question that properly executed and followed up fuels treatments — mechanical, or prescribed fires — can modify subsequent fire behavior and reduce a wildfire’s intensity. Despite the attention getting efforts of these groups, this has been a settled issue for a very, very long time. Indigenous people no doubt knew this, and in recent decades wildland firefighters do as well.
Scientists say climate change has made the American West much warmer and drier and will continue to make weather more extreme and wildfires more frequent and destructive, accelerating the need for more large-scale forest treatments.
Critics say forest thinning operations are essentially logging projects in disguise.
Opening up the forest canopy and leaving more distance between trees reduces the natural humidity and cooling shade of dense forests and allows unimpeded winds to push fire faster, said Chad Hanson, forest and fire ecologist with the John Muir Project.
Such reasoning defies the laws of physics, said other experts: Less fuel means less severe fire. Fewer trees means it’s more difficult for fires to leap from treetop to treetop.
In a tweet that linked to the Associated Press article, British Columbia-based fire ecologist Robert W. Gray wrote:
Another case of false equivalency: weight of published, peer-reviewed fact vs one or two counter factuals published in a single journal known for pushing pseudoscience.
During extreme weather and fuel conditions, such as strong winds and very low fuel moisture, fires can spread very quickly with a great deal of resistance to control igniting spot fires a mile ahead, and in some cases may burn rapidly through or jump across fuel reduction sites, possibly igniting structures. This can illustrate the importance of homeowners making structures fire resistant and reducing flammable material in the Home Ignition Zone.
But in less than extreme conditions, a fire that spreads into a recently completed fuels project will slow, be less intense, and will offer less resistance to control. A recent example of this was when the Caldor Fire in Northern California began to reach the South Lake Tahoe area, allowing firefighters to attack the fire more directly. In a live briefing on September 3, 2021 East Side Incident Commander Rocky Opliger complimented the agencies for the fuel treatments that had been accomplished over the years. He said the 150-foot flame lengths dropped to about 15-feet when the fire entered the treated areas. This allowed hand crews and engines to take an aggressive approach to suppress the fire and prevent structure loss. The video of the briefing is on Facebook; Mr. Oplinger’s comments about the fuel treatments begin at 34:10.
“Science” funded by agenda driven advocacy groups that has not been peer-reviewed should always be suspect. Settled science that has been proven for decades or even centuries, should be respected.
