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Introduction to Wildland Fire Behavior
S-190 Unit I
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Course 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 00-01-S190
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Unit 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 I. PRESENT UNIT OBJECTIVES. 01-01(1 of 2)-S190
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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 01-01(2 of 2)-S190
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Fire Triangle Heat Oxygen Fuel 01-02-S190
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Heat Transfer Radiation Convection Conduction 01-03-S190
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Wildland Fire Behavior Triangle
Topography Fuel Weather
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Group 1 — Fuels Fuel moisture Size and shape Horizontal continuity
Light fuels vs. heavy fuels Fuel loading Horizontal continuity Uniform and patchy Vertical arrangement Ground, surface, aerial 01-04-S190
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Fuel Types Grass Shrub Timber litter Logging slash 01-05-S190
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Fuel Characteristics Size and shape Fuel moisture Fuel loading
Horizontal continuity Vertical arrangement 01-06-S190
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Fuel 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 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 01-08-S190
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Categories 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 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 01-07-S190
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Fuel Loading The quantity of fuels in an area 01-09-S190
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Horizontal Continuity and Vertical Arrangement
Uniform Patchy Vertical arrangement Ground Surface Aerial 01-10-S190
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Uniform Fuels 01-11-S190
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Patchy Fuels 01-12-S190
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Vertical Arrangement of Fuels
AERIAL FUELS: All green and dead materials located in the upper forest canopy including tree branches and crowns, snags, moss, and high shrubs. SURFACE FUELS: All materials lying on or immediately above the ground 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. 01-13-S190
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Ladder Fuels Ladder fuels are areas where a surface fire can easily move into the aerial fuels
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Fire moving through Ladder Fuels
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Group 3 — Topography Aspect Slope Position of fire Shape of country
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
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Aspect North South Heavy fuels Shade Moisture Light fuels Sunny Dry
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South Facing Aspect
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North Facing Aspect
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Fire 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 Spread
Convection and radiant heat Flame is closer to fuel 01-17-S190
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Position of Fire on Slope
Fire near top of slope Slope Fire near bottom of slope has rapid spread upslope 01-18-S190
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The hazards of narrow or box canyons
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 Effect
01-19-S190
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Radiant Heat Across Narrow Canyon
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Spotting Across Narrow Canyon
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Lateral Ridge to Canyon
This fire is moving into an area of stronger wind and an enclosed area where radiant heat can collect Lateral Ridge to Canyon 01-22-S190
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Mountains Cause Channeling of Wind
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Elevation As elevation increases, temperature will decrease Trees
Shrubs Grass Sea level 01-24-S190
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Unit 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 I. RECAP UNIT OBJECTIVES. 01-25(1 of 2)-S190
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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
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