Chapter 2 Flashcards
Define fire environment and behavior
Environment: conditions that determine the behavior of a fire. Based on fuel, weather, topography.
Behavior: manner which fuel ignites, flames develop, and fire spreads. Includes other fire phenomena determined by fuel/weather/topography.
Relative humidity
(RH%): moisture in the air relative to the total amount of moisture air can hold at a given temperature. Higher temperatures can hold more moisture.
Atmosphere stability
Measured by vertical movement of air. Unstable atmosphere incl vertically developed clouds > precursor for storms. Stable resists vertical movement and may reduce or suppress fire.
Orographic lift
Movement of storm over mountain ranges. Relative humidity reaches precipitation followed by rain shadow effect on leeward side.
Fuel moisture content
Amount of moisture in fuel represented by (wet weight-dry weight)/dry*100
Foliar moisture content
Moisture content of live foliage in canopy. Follows seasonal pattern depicted by dip in spring moisture content from new growth
Equilibrium moisture content
Occurs when there is no net gain or loss of moisture between fuels and surrounding air
Time lag to equilibrium
Describes responsiveness of fuels. Effected by %RH and C = time lag varies
Five stable fuel properties
Shape/size, load, compaction, distribution/continuity, position/arrangement
Six fuel strata
Subsurface, ground, surface, ladder, aerial, crown
Six topographic properties that influence fire behavior
Terrain, slope, aspect, elevation/slope, topographic features, barriers to spread
Time and space associated with fire triangle, fire behavior triangle, and fire regime triangle
Generally, time moves from seconds/minutes > hours/weeks/days > decades/centuries. Space moves from a microsite > local > landscape > region.
How does surface-area to volume ratio of the fuels affects fire behavior?
Influences rate a fire spreads. Fuels with a higher surface area to volume ratio, such as fine fuels, burn faster than heavy fuels.
How does aspect affect fuels, fuel moisture and potential fire behavior?
Determines amount of solar radiation received, fuel load potential, and fuel load moisture
What happens to fire behavior when a cold front passes over an active fire?
Creates unstable atmospheric conditions which are favorable for burning environment.