Introduction to Wildland Fire Behavior S-190 Unit I.

IntroductioIntroduction to n to

Wildland Wildland Fire Fire

BehaviorBehavior

S-190S-190

Unit IUnit I

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

Heat TransferHeat Transfer

• Radiation

• Convection

• Conduction

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Wildland Fire Behavior TriangleWildland Fire Behavior Triangle

Fuel Topography

Weather

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

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

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.

Ladder FuelsLadder Fuels

Ladder fuels are areas where a surface fire can easily move into the aerial fuels

Fire moving through Ladder FuelsFire moving through Ladder Fuels

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

of fire season, etc. 01-15-S190

AspectAspect

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North

Heavy fuelsShadeMoisture

South

Light fuelsSunnyDry

South Facing AspectSouth Facing Aspect

North Facing AspectNorth Facing Aspect

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

Steep Slopes Cause Rapid Fire Steep Slopes Cause Rapid Fire SpreadSpread

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Convection and radiant heat

Flame is closer to fuel

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

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

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

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

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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