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Article of the Month - April, 2008 Landscaping for Fire Prevention I: Home Ignition Zones and Defensible Space. by Yvonne C. Barkley and Chris Schnepf
Towns and cities are spreading into the surrounding countryside as more and more people move out to the woods. If you live on forested property, or are considering building there, you are part of the growing wildland-urban interface – where the urban environment meets the wild.
Things were seen last year that had never been seen before. Things happened that were not supposed to happen. Any many feel that last year’s fire season was not abnormal, but the new normal. It may be muddy outside right now, or you may even still have snow on the ground, but if you live in the Inland West it is never too soon to think about the next fire season. Residents of the forested areas of Idaho should view wildfire the same way residents of the Midwest view tornadoes – an expected natural phenomenon that can devastate property and life – and prepare accordingly. The Home Ignition Zone. The most effective ways to increase the protection of your home from wildfire is to reduce the ignition potential of your home and surrounding landscape. Home ignition zones are those areas of your home and outbuildings that are the most susceptible to ignition. There are three sources of ignition. Heat can be moved from one piece of fuel to another by conduction. Larger fuels must usually be in contact with, or close to each other for conduction to transfer enough heat for kindling to occur. A home with a well defined and well maintained defensible space will be nicely protected from surface fires that are moving via conduction. A second type of ignition occurs when radiation contributes to the fire spread by preheating and drying small fuels to their ignition points. Radiation can occur with both surface and crown fires, and can ignite structures from up to 100 feet if conditions are extreme. A third phenomenon, convection, preheats surface and vertical fuels, and contributes greatly to fire spread by transporting embers which can ignite spot fires ahead of the main burn. Most homes ignite by convection from burning brands and embers that fall onto the roof of a house, a deck, or an outbuilding. New research has shown that in many fires this is the number one source of home ignitions. Your Home. In Figure 1 you will see three zones. Zone 1 includes your home. Steps have been taken to decrease and/or eliminate the ignition potential of your home. Particular attention is paid to nonflammable roofing materials, enclosing decks, soffits and overhangs, and removing debris from roofs and gutters. Figure 1. Home Ignition Zones.
Zone 1. Zone 2. Zone 3. If you have not built yet, try to place structures on flat ground. Fires burn uphill more rapidly than down or across a flat. Avoid draws, as they can serve as a chimney, creating more intense fires that spread rapidly with uphill drafts. Use fire resistant materials to build or to replace flammable materials. Tile, metal or asphalt roofing materials and brick or stucco walls are the most fire resistant. Untreated or poorly treated wood shake shingles are the least fire resistant and in many cases, offer almost certain ignition of your home.
Double pane windows and protective shutters or fire-resistant window treatments (blinds, drapes) will help insulate the inside of your house from the heat of a fire, lessening the chance of the interior becoming overheated and igniting. Make sure your chimneys are screened and construct covers for all attic and basement openings. Pay attention to places where combustible materials meet each other – a vine covered wooden fence leading up to your wooden stairs can act like a trail of gunpowder leading to a barrel of explosives. Also remove shrubs and combustible fencing from around propane tanks and woodpiles. Park boats, campers, and other flammable recreational vehicles in an enclosed area or away from your home. If possible, have power lines buried to protect them from fire and prevent them from igniting vegetation. If burying the lines is not possible contact your power company to make sure trees and branches are trimmed 10 to 15 feet away from lines.
Your Landscape. In Zone 2, approximately 100
feet around the home is surrounded by a To prepare and maintain Zone 2:
Life in the wildland/urban interface is enjoyable, but not without danger. In western forest environments, wildfire should be anticipated and planned for, not unexpected and dismissed. You have a choice – if you take precautions to protect your property it will increase your chances of escaping serious damage from wildfire. For additional information and informative figures and photos, email the UI Extension Forestry office and request a copy of Protecting and Landscaping Homes on the Wildland Urban Interface. by Yvonne C. Barkley, Chris Schnepf, and Jack Cohen. Station Bulletin No. 67, January, 2005. Idaho Forest, Wildlife and Range Experiment Station, Moscow, ID. |
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