Transcript S190 - Unit 1 - Louisiana State University

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
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
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
– 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
• Horizontal continuity
– 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
– 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
Heavy fuels
Shade
Moisture
South
Light fuels
Sunny
Dry
01-16-S190
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
01-20-S190
Spotting Across Narrow Canyon
01-21-S190
Lateral Ridge to Canyon
This fire is moving into
an area of stronger
wind and an enclosed
area where radiant
heat can collect
01-22-S190
Mountains Cause Channeling of Wind
01-23-S190
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
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