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IntroductioIntroduction to n to
Wildland Wildland Fire Fire
BehaviorBehavior
S-190S-190
Unit IUnit I
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Course ObjectivesCourse Objectives
• Identify and discuss the three sides of the fire triangle
• Identify the environmental factors of wildland fire behavior that affect the start and spread of wildland fire
• Recognize situations that indicate problem or extreme wildland fire behavior
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Unit 1 ObjectivesUnit 1 Objectives
• Describe the fire triangle
• Identify three methods of heat transfer
• List the three principle environmental elements affecting wildland fire behavior
• List three factors of fuel that affect the start and spread of wildland fire
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Unit 1 Objectives (cont.)Unit 1 Objectives (cont.)
• Describe how slope affects wildland fire spread
• List four factors of topography that affect wildland fire behavior
• Describe the dangerous conditions that can develop in a box canyon and steep narrow canyons
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Fire TriangleFire Triangle
Hea
tH
eat
Oxygen
Oxygen
FuelFuel01-02-S190
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Heat TransferHeat Transfer
• Radiation
• Convection
• Conduction
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Wildland Fire Behavior TriangleWildland Fire Behavior Triangle
Fuel Topography
Weather
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Group 1 — FuelsGroup 1 — Fuels
• Fuel moisture
• Size and shape– Light fuels vs. heavy fuels– Fuel loading
• Horizontal continuity– Uniform and patchy
• Vertical arrangement– Ground, surface, aerial
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Fuel TypesFuel Types
• Grass
• Shrub
• Timber litter
• Logging slash
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Fuel CharacteristicsFuel Characteristics
• Size and shape
• Fuel moisture
• Fuel loading
• Horizontal continuity
• Vertical arrangement
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Fuel Size and ShapeFuel Size and Shape
• Make a huge difference in how the fire will behave
–Fuel moisture–How it will spread–How fast it ignites–How well will it transfer fire to other fuels–How long and intense will it burn
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Categories of FuelCategories of Fuel
• Light fuels– Leaves, grass, shrubs
• Light fuels catch easily and burn quickly
• Because they don’t have much weight, they are consumed quickly
• These are the primary carriers of fire
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Categories of FuelCategories of Fuel
• Heavy fuels– Limbs, logs, stumps
• Heavy fuels are more difficult to ignite, and move slower than fires in light fuels
• However, expect large amounts of heat and long burning times
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Fuel MoistureFuel Moisture
• The amount of water in a fuel expressed as a percentage of the oven-dry weight of that fuel
• Size of the fuel play directly into how much moisture it will hold and how fast it can gain or lose moisture
– 1 hour – 10 hour– 100 hour– 1000 hour
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Fuel LoadingFuel Loading
• The quantity of fuels in an area
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Horizontal Continuity andHorizontal Continuity andVertical ArrangementVertical Arrangement
• Horizontal continuity– Uniform– Patchy
• Vertical arrangement– Ground– Surface– Aerial
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Uniform FuelsUniform Fuels
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Patchy FuelsPatchy Fuels
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Vertical Arrangement of FuelsVertical Arrangement of Fuels
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AERIAL FUELS: All green anddead materials located in the upperforest canopy including tree branches and crowns, snags, moss, and high shrubs.
SURFACE FUELS: All materialslying on or immediately above theground including needles or leaves,duff, grass, small dead wood, downed logs, stumps, large limbs, and low shrubs.
GROUND FUELS: All combustible materials lying beneath the surface including deep duff, roots, rotten buried logs, and other organic material.
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Ladder FuelsLadder Fuels
Ladder fuels are areas where a surface fire can easily move into the aerial fuels
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Fire moving through Ladder FuelsFire moving through Ladder Fuels
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Group 3 — TopographyGroup 3 — Topography
• Aspect– Direction a slope faces
• Slope– Steepness
• Position of fire – Top, middle, or bottom of slope
• Shape of country– Narrow canyons and box canyons
• Elevation– Relates to curing of fuels, precipitation, length
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AspectAspect
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North
Heavy fuelsShadeMoisture
South
Light fuelsSunnyDry
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South Facing AspectSouth Facing Aspect
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North Facing AspectNorth Facing Aspect
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Fire and slopesFire and slopes
• Due to convected heat, fires will move uphill 20 times faster than they will downhill.
• Flame lengths are generally pointed in an uphill direction (where more fuel is)
• Upward moving heat will preheat fuels farther up the slope
• The steeper or longer the slope, the faster the fire will spread
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Steep Slopes Cause Rapid Fire Steep Slopes Cause Rapid Fire SpreadSpread
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Convection and radiant heat
Flame is closer to fuel
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Position of Fire on SlopePosition of Fire on Slope
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Fire near top of slope
Fire near bottom of slope has rapid spread upslope
Slope
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The hazards of narrow or box The hazards of narrow or box canyonscanyons• The enclosed space of the canyons have a
tendency to channel wind
• Keeps radiant heat in the area due to the shape of the country
• Canyons expose more fuel to heat and brands
• Fires can preheat several aspects inside the canyon all at once
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Box Canyon and Chimney EffectBox Canyon and Chimney Effect
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Radiant Heat Across Narrow CanyonRadiant Heat Across Narrow Canyon
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Spotting Across Narrow CanyonSpotting Across Narrow Canyon
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Lateral Ridge to CanyonLateral Ridge to Canyon
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This fire is moving into an area of stronger wind and an enclosed area where radiant heat can collect
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Mountains Cause Channeling of WindMountains Cause Channeling of Wind
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ElevationElevation
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Trees
Shrubs
GrassSea level
As elevation increases, temperature will decrease
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Unit 1 ObjectivesUnit 1 Objectives
• Describe the fire triangle
• Identify three methods of heat transfer
• List the three principle environmental elements affecting wildland fire behavior
• List three factors of fuel that affect the start and spread of wildland fire
01-25(1 of 2)-S190
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Unit 1 Objectives (cont.)Unit 1 Objectives (cont.)
• Describe how slope affects wildland fire spread
• List four factors of topography that affect wildland fire behavior
• Describe the dangerous conditions that can develop in a box canyon and steep, narrow canyons
01-25(2 of 2)-S190