Wildland Fire Investigation, FIâ210 Origin and Cause Determination
Wildland Fire Investigation, FIâ210 Origin and Cause Determination
Wildland Fire Investigation, FIâ210 Origin and Cause Determination
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categories:<br />
Aerial fuels: All materials in the upper forest canopy<br />
Surface fuels: Materials lying on or immediately above the ground<br />
Ground fuels: Materials beneath the surface<br />
1-14 <strong>Fire</strong> Behavior Factors – Weather<br />
Weather is one of the more complex factors affecting wildl<strong>and</strong> fire because it is constantly<br />
changing <strong>and</strong> difficult to predict. The temperature of the air, ground, <strong>and</strong> fuel all influence the way fire<br />
behaves. Higher ground <strong>and</strong> fuel temperatures make it easier for the fuel to ignite <strong>and</strong> burn. There may<br />
be as much as 50º difference in temperature between fuels in the sun <strong>and</strong> those in the shade.<br />
1-15 <strong>Fire</strong> Behavior Factors – Wind<br />
One of the most important <strong>and</strong> least predictable influences on wildl<strong>and</strong> fire behavior is wind.<br />
Wind increases the amount of oxygen available, making the fire burn faster. Wind drives fire into new<br />
fuel, encouraging combustion <strong>and</strong> the spread of fire in one direction, but it can also cause rapid changes<br />
in the fire’s direction. Wind carries sparks <strong>and</strong> firebr<strong>and</strong>s ahead of the main fire, starting spot fires. Wind<br />
directly affects fuel moisture by increasing evaporation from damp spaces, carrying away moist air <strong>and</strong><br />
replacing it with drier air.<br />
1-16 <strong>Fire</strong> Behavior Factors – Relative Humidity<br />
Relative humidity is another weather factor that directly affects wildl<strong>and</strong> fire behavior. Dry air, or<br />
low humidity, takes moisture out of fuel. When the relative humidity is high, fuel absorbs moisture from<br />
the air. Remember, the size of the fuel also influences how quickly it takes on or gives off moisture. A<br />
light fuel such as pine needles responds dramatically to changes in humidity. As fuel size increases the<br />
change in fuel moisture happens more slowly. All these weather factors can change rapidly, on their own<br />
or in combination, <strong>and</strong> always affect fire behavior.<br />
1-17 <strong>Fire</strong> Behavior Factors – Topography<br />
The lay of the l<strong>and</strong>, otherwise known as topography, is the most constant of the three<br />
environmental elements affecting wildl<strong>and</strong> fire, making its influences much easier to predict than those of<br />
fuel or weather.<br />
Topography, or the lay of the l<strong>and</strong>, can be divided into these elements:<br />
Aspect<br />
Slope<br />
Position of fire<br />
Shape of country<br />
1-18 <strong>Fire</strong> Behavior Factors – Aspect<br />
Aspect, or the direction in which a slope faces, determines how much heating the fuels get from<br />
the sun. Different aspects receive sunlight at different times of day, which means fuel temperature on a<br />
given aspect will change throughout the day. South- <strong>and</strong> southwest-facing slopes are normally more