FIRE
BEHAVIOR
Three types of fire behavior
Surface fire:
Fuels at or near the surface
Ground:
Subsurface organic fuels (duff, organic soils)
Crown:
Tree crowns
Categories of fires according to human
management action:
Wildfire:
Suppression action is taken
Management ignited prescribed fire:
Ignited to meet a management objective
Prescribed natural fire:
Allowed to burn under a management plan
to preserve natural role of fire
Fire Behavior:
The Wildland Fire Environment
Weather
Topography
FIRE
Fuels
Components of the Wildland Fire Environment
Weather
•Temperature
•Relative Humidity
•Atmospheric Stability
•Windspeed and Direction
•Precipitation
Components of the Wildland Fire Environment
Topography
•Elevation
•Position on Slope
•Aspect
•Shape of Country
•Steepness of Slope
Components of the Wildland Fire Environment
Fuels
•Fuel Loading
•Size and Shape
•Compactness
•Horizontal Continuity
•Vertical Continuity
Effects of topography on fire behavior.
Fuel load
Temperature
Winds
Moisture
Effect of Aspect on Fuel Temperature and Moisture
Heaviest snows
Highest Moisture
Lowest Temperature
Wind Direction
Later Curing of Fuels
Late Snow Melt
Fuels Transition
Fuels Transition
Earlier Heating
Later Heating
Earlier Cooling
Later Cooling
Generally Lee Side of
Mountain
Generally Windward Side
of Mountain
Lightest Fuels
Lowest Fuel Moisture
Highest Temperature
Earlier Curing of Fuels
Earlier Snow Melt
Slope Affects Fire Behavior
Burning Material Rolling
Downslope
Preheating
Draft
Faster Ignition and Spread
Characteristics of Fire Behavior
FIRE INTENSITY – Heat release per unit time
(BTUs or KJ)
Fire Intensity Affected by
• Fuel loading
• Fuel moisture content
• Compactness or arrangement of
fuels
Spread Direction
Flame Height
Flaming Zone
Rate of Spread (ROS)
The distance a fire travels during a given period of time.
Burned Area
Primary factors affecting
rate of spread?
• Increased fire intensity
• Windspeed
• Steepness of slope
Rate of spread = distance/time
4 acres
16 acres
36 acres
(front)
Team Work
• Construct a sentence using your term(s)
that explains the behavior of a particular
fire situation but WITHOUT USING THE
TERM IN THE IN THE EXPLANATION– the
rest of the class should be able to
determine what the term is based on your
explanation.
Running
Creeping
Smoldering
Spotting
Spot fires
Fire brand
Torching
Crowning
Flareup
Blowup
Fire Whirls
Wildfire
Management ignited prescribed fire
Prescribed natural fire
Ground fire
Surface fire
Crown fire
Chimney effect
Slope reversal
Chimney Effect
Slope Reversal
Bottom of a
Narrow Canyon
Slope Reversal
Three types of fire behavior
Ground fire:
Subsurface organic fuels (duff, organic soils)
Surface:
Fuels at or near the surface
Crown:
Tree crowns
Categories of fires according to human
management action:
Wildfire:
Suppression action is taken
Management ignited prescribed fire:
Ignited to meet a management objective
Prescribed natural fire:
Allowed to burn under a management plan
to preserve natural role of fire
Types of fire behavior
Running – spreading quickly
Creeping – spreading slowly with low flames
Smoldering – burns without flames; barely spreading
Spotting – sparks/embers carried by wind or
combustion column or moved by gravity
Spot fires – new ignition points
Fire brand – a piece of burning material
Types of extreme fire behavior
Torching – surface fire moves into crowns of individual trees
Crowning – spreads from tree crown to tree crown
(dependent, active, or independent)
Flareup – sudden acceleration of fire spread or intensity
(short duration, for portion of fire)
Blowup – dramatic change in the behavior of the whole fire
(rapid transition to a severe fire)
Fire Whirls – vortex (gas mass with rotational motion)
Fire Affects Its Own Environment
Local Winds
Atmospheric Stability
Clouds/Precipitation
Fuel Temperature
Fuel Moisture
Wind-driven fire behavior
Plume-dominated fire
behavior (with downbursts)