Fire Environment Flashcards
Point-source fires
Start from a single point
Fire shape
Fires form an elliptical shape driven by wind/slope, burning most rapidly at the head (front), slower on the flanks (sides), and slowest at the back
Backing fire
Into wind or downslope, slow rate of spread = higher heat/area
Head fire
Pushed by wind or upslope, fast rate of spread = higher intensity
Flank fire
Burns perpendicular to the wind, burn more quickly than backfires and flames are greater in length
Rate of spread
Rate of forward spread of flaming fire front
- usually average over time
- fastest at head, intermediate at flank, slowest at back
Flame length
Measured from the midpoint of the flaming combustion zone to the tip of the flames
Topography
- slope steepness
- aspect and elevation
- slope position
- canyons
- barriers
Slope steepness
Directly affects flame length and rate of spread
Aspect and elevation
- south-facing aspects are hotter/drier (in northern hemisphere)
- higher elevations are cooler/wetter
Slope position
Fires starting at the base of a slope become larger because of the availability of fuel upslope
Canyons
- narrow canyons (reheating of fuels on opposite slope, spotting on opposite slope)
- chimney effect (unstable air conditions cause a convection current in the canyon)
Barriers
Roads, rivers, bare soil (restrict fire spread)
Fuels
Organic materials that burn in fire
- natural vegetation is primary fuel
- available fuels = capable of burning in a given fire situation
- fuels are described by type (characteristics of the fuel) and state (moisture content)
Fire whirls
Whirlwind induced by a fire and often composed of flame or ash
- occur when intense rising heat and turbulent wind conditions combine to form whirling eddies of air
- eddies can contract a tornado-like vortex that sucks in debris and combustible gases
