Chapter 1 Flashcards
Fire triangle
Heat- lightning,humans
Fuel-everything
O2- only thing that can’t be removed
Fire behaviour triangle
Fuel- fine or heavy, arrangement and continuity, fuel moisture
Topography- aspect(facing sun or not, direction, flat or slopes
Weather- wind, temperature, rh, rain
Temperature
As temp rises, more moisture evaporates and fuels get dryer
RH
Amount of moisture in the air. When high, forest fuels absorb moisture from air, when low fuels release moisture into air.
Highest during morning and late night. Lowest during late afternoon-
Flammable
Crossover
RH is less or equal to the ambient air temp. Can increase fire and alter strategies
Inversions
Cold air on valley floor and warm air on top of it. Fire burns lower intensity on cool floor but if it reaches warm air intensity grows rapidly
Wind
Drys fuels
Direction and speed affect spread rates, direction, and shape of fire
Affects amount and distance of spotting
Increase o2 to fire
Cumulonimbus cloud
Passing over fire causes extreme wind shifts
Rain
Affects moisture
Downdrafts
Bring more o2 to fire and winds. Causes flare ups and changes direction of fire spread
Fuel moisture content
Determines burn potential cause it affects ignitability. Lower moisture = more ignitable
Curing
Drying of grasslands or crops when they die. Fire has minimal spread when material is less than 50%
States of fuel
Live/green and dead
Live/green fuels
Always have some moisture,
Dead fuels
Primary drive of all wildfires. Fine dead fuels soak up rain, moisture from air and dry out quicker. Medium and large fuels take more rain to increase moisture
Fine fuels
Cured grass, leaves, things smaller than 0.6cm Ignite easily, respond quick to wind and humidity
Medium fuels
1-7 cm, dry slower than fine, more energy to ignite but burn longer, needed to hear heavy fuels
Heavy fuels
Large woody materials greater than 7cm, hard to ignite and burn slow, longer to change moisture
Fuel load
Dry weight of combustible materials per unit area
Arrangement
Distribution of combustible materials in a particular fuel type. Fuel compactness and continuity impact transfer of heat, rate of combustion, fire spread, fire intensity
Coniferous trees
Pine. Hold dead fuels like needles so more likely to burn.
Topography
Physical features of earths surface. Hills, valleys, lakes form patterns. Patterns limit or encourage fire spread
Slope
Upward or downward slant of surface.
Fuel is heated, dries quick. Fire will spread up, steeper the more fire spread. Radiation increased cause flames tilted toward fuel, convection increased due to hot air rise
Aspect
Direction slope faces. Influences amount of solar radiation fuels receive, type of vegetation on slope, moisture, temp, winds, RH
Elevation
Temp decreases with elevation, RH increases, winds increase. Winds are drastically diff between valley and ridge top. Fine fuels at high.
Shape of country
Lay of land effects fire behaviour.
Bay
In between two fingers
Finger
Elongated burn area projecting from main body resulting in jagged fire partern
Flanks
Between head and back. Parallel to main spread direction
Head
Greatest spread rate on downwind or upslope part of fire
Heel
Opposite of head. Slowest fire spread
Island
Area of unburned fuels located within fire perimeter
Types of fires
Ground, surface, crown
Ground fire
Burns in ground fuel layer. Smoulders
Surface fire
Surface layer excluding crown area. Smouldering, creeping, running
Crown fire
Advances through crown fuels in conjunction with a surface fire.
Smouldering
Fire without visible flame. No signs of spreading
Creeping
Fire spread slowly through surface fuels. Low flames
Running
Rapid spreading fire. Defined head
Spotting
Smaller fire carried outside perimeter of main fire by wind, fire whirl or convection column
Heat transfer
Burning fuels heat unburned fuels to their ig temp and combustion occurs
Convection
Movement of masses of hot air
Conduction
Physical contact
Radiation
Straight lines from warm surfaces to cooler surroundings
CFFWI System
Ratings of fire potential based off of weather. Temp, RH, wind speed and rain
FWI System
Based off of fine fuel, duff moisture codes and drought code. Initial spread, buildup and fire weather indexes
Head fire intensity
Rate of heat energy released per unit time per unit length of fire front
Head fire intensity classes
Class 4,5,6 head fires need to be fought with an anchor point
Grass fire behaviour guide
Good for judging fire behaviour in grasslands with severe burning conditions. Uses wind