Introduction to Wildland Fire Behavior S-190 Unit I

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

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

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

Fire Triangle Heat Oxygen Fuel 01-02-S190

Heat Transfer Radiation Convection Conduction 01-03-S190

Wildland Fire Behavior Triangle Topography Fuel Weather

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

Fuel Types Grass Shrub Timber litter Logging slash 01-05-S190

Fuel Characteristics Size and shape Fuel moisture Fuel loading Horizontal continuity Vertical arrangement 01-06-S190

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

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

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

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

Fuel Loading The quantity of fuels in an area 01-09-S190

Horizontal Continuity and Vertical Arrangement Uniform Patchy Vertical arrangement Ground Surface Aerial 01-10-S190

Uniform Fuels 01-11-S190

Patchy Fuels 01-12-S190

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

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

Fire moving through Ladder Fuels

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

Aspect North South Heavy fuels Shade Moisture Light fuels Sunny Dry

South Facing Aspect

North Facing Aspect

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

Steep Slopes Cause Rapid Fire Spread Convection and radiant heat Flame is closer to fuel 01-17-S190

Position of Fire on Slope Fire near top of slope Slope Fire near bottom of slope has rapid spread upslope 01-18-S190

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

Box Canyon and Chimney Effect 01-19-S190

Radiant Heat Across Narrow Canyon

Spotting Across Narrow Canyon

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

Mountains Cause Channeling of Wind

Elevation As elevation increases, temperature will decrease Trees Shrubs Grass Sea level 01-24-S190

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

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