FIREBEHAVIOR

Surface fire:

Ground:

Crown:

Three types of fire behavior

Fuels at or near the surface

Subsurface organic fuels (duff, organic soils)

Tree crowns

Categories of fires according to humanmanagement action:

Wildfire:

Management ignited prescribed fire:

Prescribed natural fire:

Suppression action is taken

Ignited to meet a management objective

Allowed to burn under a management plan to preserve natural role of fire

Fire Behavior:Fire Behavior:

The Wildland Fire The Wildland Fire EnvironmentEnvironment

Weather Topography

Fuels

FIRE

WeatherWeather

Components of the Wildland Fire Environment

•TemperatureTemperature

•Relative HumidityRelative Humidity

•Atmospheric StabilityAtmospheric Stability

•Windspeed and DirectionWindspeed and Direction

•PrecipitationPrecipitation

TopographyTopography

Components of the Wildland Fire Environment

•ElevationElevation

•Position on SlopePosition on Slope

•AspectAspect

•Shape of CountryShape of Country

•Steepness of SlopeSteepness of Slope

FuelsFuels

Components of the Wildland Fire Environment

•Fuel LoadingFuel Loading

•Size and ShapeSize and Shape

•CompactnessCompactness

•Horizontal ContinuityHorizontal Continuity

•Vertical ContinuityVertical Continuity

•Chemical ContentChemical Content

Effects of topography on fire behavior. Effects of topography on fire behavior.

Fuel loadTemperature WindsMoisture

Effect of Aspect on Fuel Temperature and Moisture

Wind Direction

Fuels Transition

Earlier Heating

Earlier Cooling

Generally Lee Side of Mountain

Lightest Fuels

Lowest Fuel Moisture

Highest Temperature

Earlier Curing of Fuels

Earlier Snow Melt

Fuels Transition

Later Heating

Later Cooling

Generally Windward Side of Mountain

Heaviest snows

Highest Moisture

Lowest Temperature

Later Curing of Fuels

Late Snow Melt

Slope Affects Fire Behavior

Preheating

Draft

Faster Ignition and Spread

Burning Material Rolling Downslope

Characteristics of Fire Behavior

FIRE INTENSITY – Heat release per unit time(BTUs or KJ)

Fire Intensity Affected byFire Intensity Affected by

• Fuel loading

• Fuel moisture content

• Compactness or arrangement of fuels

Flaming Zone

Flam

e Le

ngth

Flame Height

Spread Direction

Rate of spread = distance/time

Rate of Spread (ROS)

The distance a fire travels during a given period of time.

Burned Area

• Increased fire intensity

• Windspeed

• Steepness of slope

Primary factors affecting

rate of spread?

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.

RunningCreepingSmolderingSpottingSpot firesFire brandTorchingCrowning FlareupBlowupFire WhirlsWildfireManagement ignited prescribed firePrescribed natural fireGround fireSurface fireCrown fireChimney effectSlope reversalChimney Effect Slope Reversal

Bottom of a Narrow Canyon

Bottom of a Narrow Canyon

Slope ReversalSlope Reversal

Ground fire:

Surface:

Crown:

Three types of fire behavior

Subsurface organic fuels (duff, organic soils)

Fuels at or near the surface

Tree crowns

Categories of fires according to humanmanagement action:

Wildfire:

Management ignited prescribed fire:

Prescribed natural fire:

Suppression action is taken

Ignited to meet a management objective

Allowed to burn under a management plan to preserve natural role of fire

Running

Types of fire behavior

– 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

Torching

Types of extreme fire behavior

– 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 EnvironmentFire Affects Its Own Environment

Local WindsLocal Winds

Atmospheric StabilityAtmospheric Stability

Clouds/PrecipitationClouds/Precipitation

Fuel TemperatureFuel Temperature

Fuel MoistureFuel Moisture

Wind-driven fire behavior

Plume-dominated firebehavior (with downbursts)