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Chapter 14.1.docx

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University of Calgary
GOPH 375

Chapter 14  Canada mostly tree fires caused by people, but lightening caused fires burn more trees  Figure 14.1/14.3 – number of fires / area burned across period of time o Not necessarily correlated, one big fire can cause more damage than a bunch of little ones  Fire needs (triangle): Fuel, oxygen, and heat. Fuel is the limiting variable because oxygen (air) and heat (sun) are usually readily available. Any combustible material is fuel (trees, houses, slash [logging debris]). To fight a fire, remove any one of these 3  Backfires – a fire lit by firefighters in front of an approaching wildfire, killing fuel for the wildfire  Ladder fuels – allow small ground fires to be carried to the tops of trees, creating large wildfires, by the varying heights of vegetation.  Fire is oxygen + hydrogen + carbon, photosynthesis in reverse – plant material is heated beyond its ignition point, and reaction gives off heat in a fire. Solar energy stored by plants during their growth is released when they are burned  Wildfires recycle nutrients from plant materials back into the environment & regenerate plant communities – decomposition also does this if the climate is warm and moist  Two types of fires: figure 14.8 o Ground/surface fires – most dangerous o Crown fires – at the tops of trees; ladder effect, need something to get fire from the ground to the tops of the trees  Figure 14.10 3 Stages of Combustion – All stages occur simultaneously in a wildfire o Pre-heating – water expelled from plants/wood/fuels by nearby flames, drought or sun  Pyrolysis: thermal degradation of wood, gives off flammable gasses o Flaming combustion – pyrolized surface of the wood burns fast and hot, stage of greatest energy release. Heat is transferred in radiation, conduction, and diffusion. Pyrolysis gases fuel the surface flames, and preheat the insides of a log o Glowing combustion – fire consumes solid wood instead of pyrolized gases; active flames disappear, but the word surface still glows. Wood burns more slowly, and at lower temperatures. Slow oxidation of charred remainders Fire Styles: glowing combustion moving slowly along the ground, flaming combustion wall of fire, or crown fire moving through tree tops. The spread of fire depends on:  Fuel: chemical composition of plants, organic debris. Eucalyptus burns easily  Weather: winds bring a continuous supply of oxygen, distribute heat, push flames forward, and bend them towards preheated fuels. Without wind, a vertical column of convected heat is created and fire moves slowly. Column can interact with upper level winds that could increase fire. Strong winds pick up embers called firebrands and drop them in unburned areas, starting new blazes called spot fires  Topography: winds blowing over rugged topography experience turbulence. Fire spread fastest up slopes because the heat that rises preheats the vegetation above it  Fire behavior: rising columns of hot unstable air can spin off fire whirls; wind sucked into the base of the fire brings oxygen.  Properties that determine a fuels combustibility, and make up fuel models: chemical composition, specific heat capacity, particle length, particle cross-sectional area, load (mass of fuel per unit area), depth, bulk density, moisture content  Coniferous burn more readily, hardwood burns slowly with little flame.  Canadian Fire Behavior Prediction (FBP) has 16 fuel types divided into 5 categories: coniferous, deciduous, mixed wood, slash, open (standing grass).  Fire-danger rating uses the fuel system cross-referenced with cu
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