FIRE: Characteristics Of Structures That Burned In The 2018 Camp Fire

dWeb.News Article from Daniel Webster dWeb.News

dWeb.News Article from Daniel Webster dWeb.News

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. In some cases, the fires from homes could have had a greater impact on the overstory vegetation than the destruction of 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. Radiant heat from nearby burning structures, or flame impingement caused by the ignition of near-home explosive materials, seem to be the main causes of fire damage to surviving houses. Researchers concluded that vegetation and building modifications could significantly improve the outcome. These include improving windows and siding near neighboring structures, treating wildland fuels and eliminating near-home combustion, particularly within 1.5m of the structure.

. The authors pointed out that 7a does not include many requirements found in other building codes. However, some others incorporate more construction classes based upon anticipated radiant heat, flame and ember exposure levels. Chapter 7A, for example, does not address the interaction of components like siding, window, or the under-eave on an exterior wall.

*There are opportunities for improvement in current building codes as well as how we live in wildfire-prone WUI areas.

. The complete conclusion section of the research is below.


The results of this study support the idea that both proximities to neighboring burning structures and surrounding vegetation influence home survival with wildfire. While denser development may help protect sub-divisions from direct flame impingement by a vegetation fire 2800, and the wind-driven Almeda Fire in southern Oregon, which destroyed nearly 111 structures, it is clear that density can be a problem once buildings start to 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). Because a fire can become an urban conflagration when it is large, the proximity of nearby burning structures is crucial. These structures produce significant heat and provide a source for additional embers. To ensure density is protective, ignitions from home and other structures must 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.

. Homes must be designed and maintained so that they can resist direct flame contact and ember ignition and can withstand extended radiant heat exposure. The strong influence of nearby burning structures upon home survival may suggest that California’s Building Code should be updated to increase the standard for radiant heat exposure.

. Some possible improvements include noncombustible siding that has rating minimums that are tied to the proximity of other structures, both panes of tempered glass in windows, and deployment of non-combustible shutters. Certain options for Chapter 7A compliance are more resistant to radiant heat and flame contact and may reduce fire spread to other parts. 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. Interactions between components such as siding, window and the under-eave on exterior walls are not considered.

. Our summary of Paradise’s damaged and not-disfigured homes was consistent with other reports that showed a high percentage of home ignitions indirect to embers (Mell, et al. 2010). 3959 Embers are often ignited near home-combustibles like fences, woody mulch, and other receptive fuels. These flames and associated radiant heat then impact the home, raising awareness about the importance of combustibles in the first 1.5m (5 feet) of a building for home survival.

. To increase the building’s resistance to embers, direct flame contact and the surrounding area around it and any attached decks or steps, a reinterpretation is necessary. 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). This view was supported by the damaged home data. Few homes showed evidence of continuity with wildland firewoods that could contribute to flame impingement. However, there were many homes that had near home fuels from both manmade and natural sources that caused ember ignitions.

(*California’s Mediterranean climate continues to pose a challenge to its residents through regular wildfire exposure across the state. It will take time to adapt to wildfire, whether by changing the surrounding surface or vegetative wildland fire fuels or simply the home itself. Good news is that survival rates are improving thanks to newer construction techniques. However, with 56% of houses built after 2008 still succumbing to the Camp Fire, much room for improvement remains.

. Our data suggests that it is possible to construct and maintain buildings that are capable of surviving wildfires, even in areas like the Paradise. 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 (


Knapp, E.E., Valachovic, Y.S., Quarles, S.L. Research by et al. Housing arrangement and vegetation factors associated with single-family home survival in the 2018 Camp Fire, California. fire ecol 17, 25 (2021). 1186/s42408-021-00117-0

Author: Bill Gabbert

After working full time in wildland fire for 33 years, he continues to learn, and strives to be a Student of Fire. View all posts by Bill Gabbert

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