Demystifying the “dragon”: how homes really ignite during wildfires

Blog Post created by ryan.quinn Employee on Jul 11, 2013

Fire triangle forest
As an instructor for NFPA’s seminar “Assessing Wildfire Hazards in the Home Ignition Zone," I know that wildfire is a common event throughout many areas of the United States.  Did you know that wildfire is the easiest natural peril to mitigate? And did you know that wildfire takes place outside of “forested” areas? Many believe that if they live in the city or a suburban area that they have no wildfire risk and their odds are good, but this is a common myth. As an instructor, I am a myth-buster!  Wildfire spreads by a “set of conditions” of fuel types, not only in the forested areas or “mapped” wildfire hazard zones, but also urban and suburban areas. 

Fire behaves according to the laws that guide the combustion process.  Fire spreads as a continual process of combustion.  It is not a moving force that cannot be stopped, as conditions must continue to meet the requirements of combustion for it to continue.  The “dragon,” as some firefighters and the media may call this combustion process, is where gasses from a fuel ignite from an energy source to create a flame.  The fire triangle demonstrates that three items are needed for this chain reaction called “fire” to happen: fuel, heat and oxygen.  Remove any one of the three and the fire will die.  No more Dragon. 

When a fuel (whether natural fuel like trees and brush or an urban fuel like a house or wooden lawn furniture) is heated, it produces a gas which when mixed with air (oxygen) and ignited with a heat source, begins to burn.  To break the fire triangle, one of the three sides must be removed. Since it’s impossible to remove the air, and often difficult to have enough water is available to cool the fire to reduce the heat, firefighters often target their efforts on removing the fuel. Interrupting fuel continuity can reduce a fire’s intensity, making it controllable. 

Homes and vegetation normally ignite from convected heat (flame) or conducted heat (embers).  Homes do not normally explode from external heat and flames during a wildfire, but can and often do ignite from flame contact against exterior materials or when firebrands enter openings and cause internal ignitions. 

Homeowner efforts do make a huge difference for firefighters.  Reducing the ignitability of a home and any fuel around the home reduces fire intensity and improves firefighter and personal safety.  Firefighters are trained to efficiently suppress wildfires, but their effectiveness is reduced when they do the work during the fire that the homeowner should be doing before there is smoke on the horizon.  Moving woodpiles, cleaning gutters, closing windows and garage doors, cutting tree limbs and removing brush and combustibles against the home should be the homeowner’s responsibility before the fire -- not the firefighter’s job. 

Residents need to understand there will never be enough fire fighting resources to protect every house during a large catastrophic wildfire event.  But residents can improve their odds against wildfire this season.  Residents need to take action now and encourage others in their neighborhood to do the same.  Visit Firewise.org and get educated on identifying fuel hazards and reducing ignitions risks and developing evacuation options.  By doing this the losses of lives of firefighters and residents and the destruction of homes from wildfires can be significantly reduced.