Researchers evaluate how fences can spread fires and ignite structures

Tests fire hazard fences
Examples of very high hazard fences and mulch: A) parallel privacy fences, B) double
lattice fences, C) wood-plastic composite #1 fence, D) good neighbor fence, E) rubber mulch. (From the NIST research)

Three weeks ago a television station in Dallas, FOX 4, streamed live video as a grass fire spread across a field and reached densely-packed houses, eventually destroying 9 and damaging another 17. There were several reasons why the structures were so vulnerable, including medium-heavy vegetation in the field adjacent to the property lines, very little impact from efforts of the fire department to stop the spread, no air support, and wood fences that connected all of the properties on the rear and sides of the homes.

fences burn fire Texas homes destroyed
Parallel fences burn as grass fire spreads into neighborhood in Balch Springs, Texas, July 25, 2022. Image from video by FOX 4 Dallas-Fort Worth.

On August 10 the National Institute of Standards and Technology (NIST) published results of 187 experiments that examined how fire spread toward a structure is affected by combustible fences and mulch under conditions that may be encountered in a wildland-urban interface (WUI) fire. They looked at mulch only, fence only, fence plus mulch, parallel fences, and long range firebrands. The materials studied were western red cedar, California redwood, pine, vinyl, and wood-plastic composites. Fence styles included privacy, lattice, and good neighbor (board on board).

A small structure was located between zero and up to six feet downwind of the fence or mulch bed as a target for flames and firebrands. A target mulch bed at the base of the structure tested the ability of firebrands produced by the burning fence and mulch bed to ignite spot fires that threatened the structure.

While not many homeowners place store-bought mulch below their fences, it can be common for debris to build up along the base on one or both sides. The amount and flammability can be extremely variable, but the researchers’ use of mulch gave them control over the flammable material which could be consistently duplicated in their experiments.

The study found that firebrands capable of igniting spot fires downwind were generated by nearly all combinations of fence and mulch tested in this study. All wood fences with mulch at the base caused spot fires in the target mulch bed. Spot fires were often ignited within a few minutes of mulch and fence ignition. Shredded hardwood mulch and pine bark mulch burned and emitted firebrands for longer than an hour. Ignition of spot fires was also demonstrated from firebrands transported by the wind over distances as far as 156 feet from the burning item under high wind conditions and over a paved surface.

The research generated a number of recommendations:

  • Avoid parallel fences, to reduce exposure to large flames. Parallel fences can result in highly hazardous fuel accumulation corridors that are difficult to access and maintain. Spacing of 3 feet between fences is not sufficient.
  • Avoid proximity to other combustible fuels, to reduce fire intensity and limit fire spread. This includes fuels above the fence and fuels across parcel boundaries. Avoid mulch at base of fence.
  • Avoid proximity of combustible fences to residence, including neighboring residence, to prevent direct ignition.
  • Fire spread is more likely with wood and wood-plastic composite fences than with fences made of vinyl or noncombustible materials such as stone, brick, or steel.
  • Keep fence and yard clear of debris, to reduce the amount of fuel and potential pathways for fire.
  • Harden structures against firebrands to prevent structure ignition from embers produced by fences or other combustible sources.

The video from the July 25 fire in Texas does not clearly show the fences between the residences, but it is likely that they directly connected to the structures. An example is seen in the photo below of two homes in Superior, Colorado, one of the communities devastated by the Marshall Fire that destroyed 991 structures south of Boulder December 30, 2021.

Fence connecting houses fire spread hazard
File photo of fence connecting houses in Superior, Colorado. July, 2012 Google image.

The images below are from the FOX 4 Dallas-Fort Worth video shot July 25, 2022.

fences burn fire Texas homes destroyed
Fences burn as grass fire spreads into neighborhood in Balch Springs, Texas, July 25, 2022. Image from video by FOX 4 Dallas-Fort Worth.
fences burn fire Texas homes destroyed
Fences burn as grass fire spreads into neighborhood in Balch Springs, Texas, July 25, 2022. Image from video by FOX 4 Dallas-Fort Worth.
fences burn fire Texas homes destroyed
Fences burn as grass fire spreads into neighborhood in Balch Springs, Texas, July 25, 2022. Image from video by FOX 4 Dallas-Fort Worth.

Most structures that burn in a wildfire are not ignited by direct flame impingement, but by burning embers that are lofted and carried downwind ahead of the fire.  At Wildfire Today we first covered the role of embers in igniting structures in 2010, a concept brought into the public consciousness by Jack Cohen, a researcher at the Missoula Fire Science Lab. To reduce the chances of a home burning in a wildfire, the most bang for the buck is to concentrate on the Home Ignition Zone. The flammable material near the structure needs to be modified, reduced, or eliminated to the point where multiple burning embers landing in the zone will not propagate the fire and spread to the structure.

More information: Six things that need to be done to protect fire-prone communities

Thanks and a tip of the hat go out to Gerald.

New California law requires seller of home to disclose vulnerability to wildfires

EIler Fire Home
One of the homes that survived the Eiler Fire in northern California, August, 2014. Photo by Bill Gabbert.

Beginning January 1 in California the seller of a home in a designated high fire area built before 2010 must disclose to the buyer conditions that make the home vulnerable to wildfires.

The seller must provide documentation stating that the property is in compliance with local laws pertaining to defensible spaces or local vegetation management laws. If there is no such local law, the seller shall provide documentation of compliance with state law, assuming the seller obtained such documentation within six months prior to entering into the transaction. But if neither of the above, the seller and the buyer must enter into a written agreement in which the buyer agrees to obtain documentation of compliance with defensible space or a local vegetation management ordinance after close.

Here are the details from the legislation:

Disclosures re Home Hardening

Beginning January 1, 2020, if a seller, after completion of construction, has obtained a final inspection report regarding compliance with, among other things, home hardening laws (Gov’t Code 51182 and 51189*), the seller shall provide to the buyer a copy of that report or information on where a copy of the report may be obtained.

Beginning January 1, 2021, this law requires for properties located in high or very high fire hazard severity zones for homes built before 2010, delivery of a notice to include the following three items:

1. A statutory disclosure that includes information on how to fire harden homes as follows:

“This home is located in a high or very high fire hazard severity zone and this home was built before the implementation of the Wildfire Urban Interface building codes which help to fire harden a home. To better protect your home from wildfire, you might need to consider improvements. Information on fire hardening, including current building standards and information on minimum annual vegetation management standards to protect homes from wildfires, can be obtained on the internet website http://www.readyforwildfire.org.”

2. Disclosure of a list of features that may make the home vulnerable to wildfire and flying embers if the seller is aware. The list includes, among other things, untreated wood shingles, combustible landscaping within five feet of the home, and single pane glass windows.

3. On or after July 1, 2025, a list of low-cost retrofits re home hardening (listed pursuant to Section 51189 of the Government Code*). The notice shall disclose which listed retrofits, if any, that have been completed during the time that the seller has owned the property.

Potential point of sale compliance requirements re defensible space or local vegetation management laws

Beginning July 1, 2021 seller of property in high or very high fire hazard zones shall provide documentation to the buyer stating that the property is in compliance with laws pertaining to state law defensible spaces (Public Resources Code 4291**) or local vegetation management ordinances, or in certain cases the buyer and seller will agree that the buyer is to obtain the documentation after close as follows

1. If there is a local ordinance requiring the seller to comply with state law governing defensible spaces (PRC 4291**) or a local vegetation management ordinance, the seller shall provide the buyer with: 1) a copy of the documentation of such compliance, and 2) information on the local agency from which a copy of that documentation may be obtained.

2. But If no such local ordinance exists, and the seller has obtained an inspection from a state, local or other government agency or qualified nonprofit which provides an inspection with documentation for the property, the seller shall provide the buyer with: 1) the documentation of the inspection if obtained within six months prior to entering into a transaction to sell the real property and 2) information on the local agency from which a copy of that documentation may be obtained.

3. If seller hasn’t obtained documentation of compliance per 1 or 2 above, then the seller and buyer shall enter into a written agreement stating that the buyer agrees to: a) obtain documentation of compliance per the local ordinance or b) if there is no such local ordinance, the buyer shall, within one year, obtain documentation of compliance as long as there is a state, local or other government agency or qualified nonprofit which provides an inspection with documentation of compliance for the property.

This law also requires the California Office of Emergency Services (Cal OES) to enter into a joint powers agreement with the Department of Forestry and Fire Protection (Cal FIRE) to administer a comprehensive wildfire mitigation and assistance program to encourage cost-effective structure hardening and facilitate vegetation management, contingent upon appropriation by the Legislature.

Data about structures that were destroyed by wildfires in each state

structures burned Almeda Drive Fire Phoenix Talent Oregon
Devastation from the Almeda Drive Fire in the area of Phoenix and Talent in southern Oregon. Screenshot from video shot by Jackson County on September 8, 2020.

The traditional way — and the easiest way — to compare wildfire seasons is the number of acres burned. That figure is fairly straightforward and reliable, at least for data within the last 35 years; before 1984 the data is questionable.

But blackened acres does not tell the whole story about the effects of fires on humans. A 50,000-acre fire in a northwestern California wilderness area has fewer direct impacts on the population than, for instance, the 3,200-acre Almeda Fire that destroyed 2,357 residences in Southern Oregon a few months ago.

Top most destructive wildfires in the United States
Top most destructive wildfires in the United States. Headwaters Economics.

Headwaters Economics has built a user friendly interactive data base of the number of structures, by state, destroyed by wildfires from 2005 to 2020. It presumably includes all structures, including back yard sheds, other outbuildings, commercial buildings, and residences.

Here are three screenshots, examples for the entire U.S., Colorado, and Montana.

Top most destructive wildfires Montana
Top most destructive wildfires in Montana. Headwaters Economics.
Top most destructive wildfires Colorado
Top most destructive wildfires in Colorado. Headwaters Economics.

The best way to prevent homes from being destroyed in a wildfire is not clear cutting or prescribed burning a forest, it is the homeowner reducing flammable material in the Home Ignition Zone. This includes spacing the crowns of trees at least 18 feet apart that are within 30 feet of the home, 12 feet apart at 30 to 60 feet, and 6 feet apart at 60 to 100 feet. The envelope of the structure itself must be fire resistant, including 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. When implemented, Chapter 7A of the California Building Code, regulates these features.

firewise wildfire risk home tree spacing
Firewise vegetation clearance recommendations. NFPA.

For more information: Six things that need to be done to protect fire-prone communities.

And, Community destruction during extreme wildfires is a home ignition problem. Here is an excerpt from the article written by Jack Cohen and Dave Strohmaier:

Uncontrollable extreme wildfires are inevitable; however, by reducing home ignition potential within the Home Ignition Zone we can create ignition resistant homes and communities. Thus, community wildfire risk should be defined as a home ignition problem, not a wildfire control problem. Unfortunately, protecting communities from wildfire by reducing home ignition potential runs counter to established orthodoxy.

After the Tubbs Fire, homes in California town are being rebuilt without strong building codes

Above: Homes being rebuilt in the Coffey Park area of Santa Rosa. Screenshot from Sacramento Bee video.

In Santa Rosa, California the 1,200 homes that were destroyed in the 2017 Tubbs Fire are being rebuilt without a requirement that they adhere to the stricter building codes required in rural areas of California that would make them more resistant to being consumed in the next wildfire.

From the Sacramento Bee:

…Coffey Park [neighborhood] is rebuilding quickly: The community organization Coffey Strong says more than half of the 1,200 homes that burned down in 2017 are finished, and hundreds more are under construction.

But some wildfire experts wonder if Coffey Park isn’t courting danger by ignoring a state building code designed for wildfire-prone areas.

“They’re setting themselves up for the next disaster,” said Chris Dicus, a wildfire expert at Cal Poly San Luis Obispo. “I was disappointed to see they didn’t build up to code.”

Coffey Park residents seem resigned to the risk of another fire. They consider it part of the cost of living in a neighborhood they love. When asked about building codes, they say yes, another monster like the Tubbs Fire would be devastating — but no amount of fire-resistant roofing would likely change that.

“If it’s going to burn down, it’s going to burn down,” said Charlie Catlett, a retired physician who moved back home a little more than a week ago, after the latest evacuations were over.

Chapter 7A of the California Building Code designed for the state’s areas at high risk from wildfire can be optionally adopted by cities, but is mandatory in rural areas designated by CAL FIRE as being at high risk of wildfires. It lays out standards for roofs, exterior walls, vents in exterior walls and attics, windows, exterior doors, decking, and outbuildings.

Analysts studying the aftermath of the Camp Fire which destroyed much of Paradise, California found that homes built to fire-safe standards had a much higher survival rate than those that were not. Beginning in 2008 new construction in the city was required to follow Chapter 7A. Fifty-one percent of the homes built under that standard survived, while only eighteen percent built before 2008 did.

Headwaters Economics found that the cost of building a fire-resistant home is about the same as a standard home.

Adopting sensible building codes is very important, but a holistic approach is required to keep from repeating wildfire disasters:

  1. Home spacing/ lot size
  2. Envelope of the structure itself
  3. Home ignition zone
  4. Community infrastructure and planning
  5. Wildland-urban interface

In April, 2019, we covered these five categories in more detail.

Some home insurance companies refusing to renew policies in wildfire-prone areas

Firewise defensible space structure

One of the most serious problems facing firefighters today is the movement of residents into the Wildland/Urban Interface, the WUI. As a wildfire spreads toward flammable structures that are near or in some cases surrounded by burnable vegetation it can be very difficult to protect them. Often as a fire grows in a WUI area containing dozens or hundreds of homes there are not enough firefighters to park a fire engine at every house.

Some structures are easier to protect than others. “Firewise” refers to homes that are designed and maintained to be fire resistant. A few burning embers (that can be transported in the wind for a mile) in most cases will not ignite a home built to withstand fire. It is the other homes, with flammable siding, roofs, and decks, and that have brush or trees providing an efficient path for the fire to spread up to the structure, that is a nightmare for the fire department. In some cases as a fire approaches, this second category of homes will be written off since it may not be possible to save them, even with a fire truck parked in the driveway. Without vegetation clearance of 30 to 100 feet, it can be unsafe for firefighters to remain at the site as an intense fire approaches.

Gunbarrel Fire
Firefighters at the Gunbarrel Fire west of Cody, WY apply foam and install sprinklers at Goff Creek Lodge, August 26, 2008. Photo by Michael Johnson.

A difficult to defend home is not only a problem for the owner, but it also affects the community. As it burns in a wildfire, it creates huge amounts of radiant and convective heat. Combined with the airborne burning embers put into the air as it burns, it can ignite other homes nearby. If multiple unprepared homes burn, the effects of the conflagration are multiplied making it difficult for even Firewise structures to survive. In addition, unprepared homes suck up more firefighting resources, which can make it difficult or impossible for there to be enough firefighters, crews, engines, and aircraft to suppress the wildland fire — they are often tied up because of some irresponsible residents.

In a perfect world all structures in a WUI would be Firewise. Inevitably, however, a sizeable percentage of homeowners will do nothing to make their structures defensible. There are two ways to encourage, or even force, them to take action before a fire strikes. Zoning laws and insurance companies. Laws can, for example, ban wood shingle roofs, and require vegetation clearances up to 100 feet, as well as other requirements. Many jurisdictions do this.

Insurance companies have an extremely powerful tool at their disposal that is rarely used. According to the NW News Network, at least two companies in Washington and Oregon are refusing to renew the policies for some home owners, or for structures in wildfire prone areas.

Below is an excerpt from NW News:

Some insurance companies are choosing not to renew policies in wildfire-prone areas of the inland Northwest. That’s sending home owners scrambling to find new coverage for their properties. Northwest-based insurers such as Pemco and Grange Insurance are getting choosier about how much risk they’ll take on. This according to property owners who’ve been dropped recently and posted about their frustrations online.

One customer from Chelan, Washington, complained Pemco refused to renew her homeowners insurance despite 17 years with no claims. The common thread among the non-renewals is location in wildfire country.

Oregon’s insurance regulators looked into this and said some insurers updated their wildfire risk rating models.

“There have been some non-renewals, rate increases, and moratoriums on new business, because updated risk models showed certain areas to be at especially high risk of wildfires,” wrote Jake Sunderland, a Department of Consumer and Business Services spokesman, in an email.

Refusing to write policies in a large area is not the best solution. Some companies will only insure structures after inspecting them to be sure they are Firewise and have defensible space.

Creating Defensible Space Around Utility Poles

defensible space power poles

Above: The power pole hazard mitigation crew’s sawyer flush cuts a palo verde stump.

By Tom Story

“As Arizona’s largest utility, there are fire risks we have to manage,” said Wade Ward, Fire Mitigation Specialist for Arizona Public Service (APS). “The primary goal of fire mitigation is to prevent fire from ever happening. The second is to provide safe and reliable electricity to the communities APS serves.  Just as important is the ability to provide for firefighter safety around our system in the event of a fire”, Mr. Ward continued.  “With five thousand miles of transmission and twenty-eight thousand miles of distribution it is hard not to have our system affected by wildland fire.  When this happens, APS’s priority is providing a safe environment for crews to work in”.

defensible space power poles
In Cave Creek, AZ; Wade Ward, Fire Mitigation Specialist for Arizona Public Service, sizes up a palo verde tree slated for removal as part of the APS Defensible Space Around Poles program.

Mr. Ward knows fire (he joined APS after his fire career at the Prescott Fire Department) and he has seen factors like drought, climate change and forest management set the stage for larger and more powerful wildland fires.  “It is becoming more evident that due to extended drought over the past decade forest and vegetation ecosystems have been stressed from the lack of regular moisture compounded by shorter drier winters and longer warmer summers,” Mr. Ward said.

APS sends out inspectors to identify hazardous vegetation in violation of its safety and reliability clearance standards as well as violations of the National Fire Code and the Urban Wildland Interface Code (which state that a utility with equipment attached to the pole must clear all vegetation 10 feet in all directions including 10 feet from the ground). The area around the pole is cleared by work crews to create defensible space.  “There are approximately 70 thousand poles within our system that we will have on a three year return cycle to maintain Defensible Space Around Poles (DSAP)” said Mr. Ward.

defensible space power poles
Other crew members cut up and feed the branches into a chipper.

The clearing is being done using manual methods (including chain saws, string trimmers and other hand tools) and where approved is followed by the application of herbicide in compliance with Environmental Protection Agency’s Integrated Vegetation Management practices. APS has prioritized the treatment of subject poles by utilizing data derived from a risk assessment done across the state. Mr. Ward continued; “It is a part of our core values at APS Forestry to manage vegetation and the environment by balancing benefits to create healthy forests and safe reliable energy”.

Mr. Ward finished his remarks noting, “In 2016 we created 110 acres of defensible space around the state of Arizona. One pole at a time”.

defensible space power poles
Putting the finishing touches on the cleanup around one of the Arizona Public Service power poles in Cave Creek, AZ.