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.
The video below produced by the New Jersey Forest Fire Service elaborates on this concept. It is queued up to 1:42 where the issue is addressed.
More information is in our articles tagged “Home Ignition Zone.”
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12 thoughts on “In a wildfire burning embers transported downwind are what cause most structures to burn”
Right ON! I spoke with Jack via phone while the Cedar Fire (2003) was still burning; he was on another fire in San Bernardo County, and came down to investigate the Cedar. He told me about observing tall eucalyptus trees with scorched bark–on the side facing the burned-out buildings, and NOT on the side facing the chaparral.
Rick Halsey and I both wrote Op-Ed pieces for the San Diego Union-Tribune; I’ve forgotten what his was about, but my was about embers. Both are on Rick’s website https://californiachaparral.org/
I’ve learned a lot from, and am ever grateful to Jack, and from Eamor Nord, Clive Countryman, and others from the Western Region Fire Lab, whose brains I picked when I was staff/chair for the “task force” on open space and fire hazard reduction in 1970-71 following the Kitchen Creek fire. We drafted a report, but the City Manager had talked with a Ph.D. from UC who told him that chaparral was “degraded grassland” and needed to be cleared and seeded to stop the fires. The report never was published.
I watched the fire from my back deck of my plastered, eave-boxed, class C roofed house while the big impact-head sprinklers wet down the deck and about fifty-feet out into the canyon below. In doing some of the library (no Internet then) research for the 1971 report I found an article about an Australian who lived in the outback who had invented his own on-site, independent, automatic structure-fire suppression system designed to cover his entire structure with water as thermocouples heated up at some distance away in the bush.
I am finally working on my own version of the on-site system. While I believe that minimal fuel separation (plus a fudge-factor, of course) can be adequate for defensive space, I don’t want to count on anyone be there to defend, especially downwind of a big wind-drive fire. Too many houses with defensible space have been burned–they just don’t get the publicity. I want a back-up. And I want some vegetation upstream to intercept embers.
In March of 2017 a group called the Institute for Catastrophic Loss Reduction released a document regarding structure losses in the 2016 Fort McMurray fire (Horse River Fire). Written by Alan Westhaver, the report titled “Why some homes survived: Learning from the Fort McMurray wildland/urban interface fire disaster”, does a nice job of highlighting how the ember shower, and subsequent urban conflagration did so much damage. Mr. Westhaver’s report confirms what Jack Cohen and many others have been saying years, FireSmart success starts at the home.
I believe the Australians were the first ones to bring to light the significant role of spotting in home destruction. See:
Barrow, G.J. 1945. A survey of houses affected in the Beaumaris Fire, January 14, 1944. Journal of the Council for Scientific and Industrial Research 18(1). 11 p. (https://www.bcs.asn.au/wp-content/uploads/2018/03/fire1944.pdf)
Wild Rose Fire Behaviour
Leduc County, Alberta
Thanks for this Chris. In the next few days, we will be releasing a forensic examination of the June 2021 fire that levelled almost all of Lytton, BC. The report was written by – wait for it – Alan Westhaver and Jack Cohen. Keep an eye on http://www.iclr.org, should be up very soon.
Glenn McGillivray, Managing Director, ICLR
There is no doubt embercast is the cause of many burndowns in the rural areas, but let’s not ignore that fact that many of the homes burned during wildfires are in a more urban setting. Recent studies ( Knapp et al 2021 and Kramer et al 2019 ) have shown that radiant heat from adjacent structures have been a huge factor contributing to house to house spread. Examples are the Camp fire as it spread through Paradise and the Tubbs fire as it spread into the Coffey Park subdivision in Santa Rosa.
To me this demonstrates we need to continue to emphasize clearance in the wildland setting, but spread the message into towns in the WUI that urban dwellers need to be aware of their vulnerability. Houses that are built 6 to the acre with 20 feet of spacing don’t leave much room for defense, but homeowners should be taught to keep that area between the houses free of combustibles.
We’ve also learned that the tactic of Fire Front Following with engines is effective and has saved many homes.
While we’re talking structure defense, would someone please comment and educate me on the success or failure of the Federal practice of foil wrapping structures for fire defense ? How does it compare with a gel or foam application?
Good point, Royal, about the spacing of structures. Thank you.
Very timely, Bill. Today I’ve watched a 35 acre brush fire in Laguna Niguel (Orange County, CA) spread upslope in heavy brush (now 150 acres), igniting (at this count) at least a dozen multi-million dollar homes. Most assuredly embers ahead of the main fire caused all the initial ignitions. The property loss is continuing, and there are many homes in the fire path. Firefighters are taking a lot of heat and smoke to work the fires. https://www.facebook.com/ktla5/videos/673881167009804
Hi Royal. I just happened to see this comment and it reminded me that I’ve been meaning to see if we could get together and talk at your convenience. Thanks
“To me this demonstrates we need to continue to emphasize clearance in the wildland setting . . .”
We used to think that “clearing to mineral soil” was THE WAY. That might be expeditious, but adequate fuel separation within the defensible zone may produce more lasting results–primarily because of the rapid regrowth of combustible fuels, even flash fuels, consisting largely of annual weeds and re-sprouting. In fact, I long ago recommended (repeating what I learned from the researchers at the Western Region Fire Lab–“Wildland fuels larger than 0.5 inches in diameter seldom, if ever, are consumed in the flame-front) that limbing high enough to prevent ignition of fuels near the understory of trees and large shrubs or removing combustible fuels (<0.5 inches dia.) Aim for packing ratios that can't spread. Also, this approach produces a lot less trimmings to haul away. Leave the chain-saw home. w
From the video footage one can see, through the smoke, spot fires in structures ahead of the flame-front.
Yes, Royal–ALL good points. I’ve tried to make the point that the spacing between structures should be more than that for defensible space, due to the increased radiant and convective heat and burn period of structures. Or anything that will ignite thereby. Structures themselves can throw veritable snowstorms of embers too, enough to pile up in inside corners. Ever find evidence of the latter in a post-burn analysis?
Would you briefly describe the best technique for “Fire Front Following with engines,” and its contextual limitations?
Copied from the FireScope WUI Structure Defense Guide:
FIRE FRONT FOLLOWING – a follow up tactic employed when Check and Go, Prep and Go,
or Bump and Run tactics are initially used:
• A tactic used to come in behind the fire front.
• This action is taken when there is insufficient time to safely set up ahead of the fire or the
intensity of the fire would likely cause injury to personnel located in front of the fire
• The goal of “Fire Front Following” is to search for victims, effect perimeter control,
extinguish spot fires around structures, control hot spots and reduce ember production.
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