Wildfires_partI_Notes

Wildfires_partI_Notes - 1 For some species, wildfires are...

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For some species, wildfires are crucial for survival (see below), i.e. wildfires are truly “natural” phenomena. With the development of rural areas and the development of Wildland/Urban interface (see below), wildfires have become a threat to lives and properties. Avoiding wildfires at all means is not a feasible or viable option since the accumulation of litter in a forest equates to the accumulation of fuel for future fires. Learning to live with wildfires and wildfire risk is therefore a challenge. 2
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There are three primary ingredients that are necessary to ignite and maintain a fire: oxygen, heat, and fuel. These ingredients make up the fire triangle. Take one away and the fire dies out. Recently, the fire triangle has been replace by the fire tetrahedon, which includes a fourth element: the ability to maintain a chemical reaction or combustion, i.e. some fires to not necessarily thrive on heat but feed off a chemical reaction. 5
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The life cycle of a wildfire has three stages: pre-ignition, combustion, and extinction. The pre-ignition stage starts by heating fuel (e.g. scorching, radiating from flames). A good example of pyrolysis is burning food. When was the last time, you toasted your bread too long and got nothing but charred toast? 6
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In order to start the combustion process, an ample amount of fuel is required or the fire may burn out and not spread. If the fire has enough fuel to spread, then ignition will occur continuously along the leading edge (fire front) of the fire. Wildfires burn in two primary ways: flaming or glowing combustion. Flaming combustion represents the fast, high-temperature burning of fuel with flames that sometimes can be seen from miles away. Flaming combustion can give leave large amount of residual unburned material. Glowing combustion happens slowly, at lower temperature, and there are usually no visible flames. 7
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types often progress from one to the next, but that is not necessarily the case. Ground fires burn primarily in the thick layers of organic material on forest floor and/or within soil. Ground fires burn, for example, old root networks, peat, and compact litter. The ignition source for a ground fire can be spontaneous combustion (oxidation), lightning or a surface fire. Ground fires spread slowly and their smoldering can last for months since they are not influenced by wind. Surface fires burn litter and vegetative matter on forest floor such as underbrush (incl. branches). The intensity of surface fires depends on the type of fuel and prevalent wind conditions. If there is not a whole lot of litter, the fire moves rather rapidly without damaging mature. Surface fires move generally at a speed of less than 6 mph. 9
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This note was uploaded on 04/03/2010 for the course DSM 2000 taught by Professor Romolo during the Spring '08 term at LSU.

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Wildfires_partI_Notes - 1 For some species, wildfires are...

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