Basic Wildland Fire Management

Fire Fire EnvironmentEnvironment

ObjectivesObjectives

Upon completion of this section, you will be able to:1. Explain significance of cold fronts, thunderstorms

and upper ridge breakdowns on fire environment2. Describe 4 weather factors and their influence on

FB3. Describe 4 topographic factors and their influence

on FB4. Describe 4 fuel factors and their influence on FB5. Name 3 types of fire6. List parts of fire7. Describe 6 components of FWI System8. Recognize fire behaviour warning signals

Basic Wildland Fire Management

Fire TriangleFire Triangle

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Phases of CombustionPhases of Combustion

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Heat Transfer ProcessHeat Transfer Process

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• 3 heat transfer processes:– Radiation: Movement

through air– Convection: Movement

of hot air masses– Conduction: Movement

through solid matter• Mass transport another

related form of heat transfer

Fire Behaviour TriangleFire Behaviour Triangle

Basic Wildland Fire Management

WindWind

• Drives direction of fire spread• Bends flame, heating, drying

and igniting new fuels• Carries embers into new fuels• Feeds more oxygen to fire• Can increase/decrease fuel

moisture depending on airmass

Basic Wildland Fire Management

TemperatureTemperature

• Temperature affects RH which inturn affects fuel moisture

• Temperature also influences ease of ignition• Variations result of time of day, elevation, land

surface, amount cloud cover and/or wind• Inversions bring different regimes of

temperature, RH and wind to a fire site

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Relative HumidityRelative Humidity

• Directly effects of fuel moisture

• When RH >35%, fine fuel moisture increases

• Variations in RH depend on proximity to water, amount of vegetation and/or frontal boundaries

• When fuels regain moisture, it’s known as recovery

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PrecipitationPrecipitation

• Duration rather than amount of precipitation determines effect of fuel moisture

• Fuel complex will affect distribution of moisture• Fine fuels react quicker to moisture changes

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SlopeSlope

• Slope affects rate of spread– Flames are closer to fuels so fuels are preheated– Burning logs, etc. can roll into unburned fuels and

accelerate uphill• Wind follows predictable flow pattern

– Downslope winds can be associated with glaciers, etc.

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AspectAspect

• More direct sunlight on SW slopes therefore higher temperatures, lower RH, lower FMC and lower fuel loading

Basic Wildland Fire Management

E

N

S

W

Tem

pera

ture

1200LST

TerrainTerrain

• Narrow, steep drainages act like chimneys for fire to channel up

• Narrow draws can also be affected by radiant heat on opposite slope

• Eddy effects are prevalent near ridge tops and convergence of two or more drainages

Basic Wildland Fire Management

WindWind

• Topographical features can steer synoptic winds

• Local mountain winds result of daytime heating

• Land and sea breezes are local winds that result from temperature and pressure differences between land and water

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Unstable AtmosphereUnstable Atmosphere

• Indicators of stable atmosphere:– Clouds in layers– Winds steady and light– Poor visibility

• Indicators of unstable atmosphere:– Clouds grow vertically– Lots of lightning– Gusty, erratic winds

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Cold FrontCold Front

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ThunderstormThunderstorm

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Upper Ridge BreakdownUpper Ridge Breakdown

• Implications of temporary URB:– Lightning outbreak– Strong, gusty surface winds and abrupt wind

shifts– Spotty precipitation of variable amount– Possible severe thunderstorms– Return to warm and dry conditions

• Permanent URB result of major re-organization of weather pattern

Basic Wildland Fire Management

Fuel CharacteristicsFuel Characteristics

• Fuel Moisture Content• Fuel Size: higher surface:volume

ratio means less time to ignite• Fuel Loading• Fuel Spacing

– Vertical spacing may be continuous or separated

– Horizontal spacing may be continuous or patchy

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Types of Wildland FireTypes of Wildland Fire

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Parts of a FireParts of a Fire

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Canadian Forest Fire Danger Rating Canadian Forest Fire Danger Rating SystemSystem

• National system for rating risk of forest fires in Canada

• Major subsystems:– Fire Weather Index System– Fire Behaviour Prediction System

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Fire Weather Index SystemFire Weather Index System

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Fuel Moisture CodesFuel Moisture Codes

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Fuel Moisture Code Represents Time Lag24hr Rain Needed

to Lower Value

Fine Fuel Moisture Code (FFMC)

Surface litter 2/3 day 0.6mm

Duff Moisture Code (DMC) 5-10cm duff 12 days 1.5mm

Drought Code (DC) 10-20cm duff 52 days 2.9mm

N.B. Time lag is time required for fuel to lose 2/3 of its moisture under standard drying conditions (i.e. 25oC and 45% RH)

Fire Behaviour IndicesFire Behaviour Indices

• Initial Spread Index (ISI) is measure of expected rate of fire spread

• Buildup Index (BUI) is measure of amount of fuel available for combustion

• Fire Weather Index (FWI) is general index of fire danger

Basic Wildland Fire Management

Interpreting Codes & IndicesInterpreting Codes & Indices

Basic Wildland Fire Management

Component

Rating Interpretation

FFMC<77 Generally a fire will not start without a concerted effort

>94 Almost 100% of ignition sources will ignite forest fuels

DMC

<20 Considered point of extinguishment, fire unlikely to be sustained

>40 Fuels in this class is available for combustion

DC

<300 Very little involvement of this fuel in most fires

>500 Extensive fuel involvement, intense fires, difficult mop-up

ISI

<10 When FFMC is less than 86, fire spread generally is not great

>10 Rapid spread rates that escalate rapidly as FFMC increases

BUI<40 Meduim-heavy fuels not a significant factor

>100 Full involvement of fuels in this class

FWI 101FWI 101

Basic Wildland Fire Management

Given the following information, what type of fire behaviour do you expect?

Fine Fuel Moisture Code (FFMC):

Duff Moisture Code (DMC):

Drought Code (DC):

Initial Spread Index (ISI):

Buildup Index (BUI):

Fire Behaviour Prediction SystemFire Behaviour Prediction System

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Fire IntensityFire Intensity

Basic Wildland Fire Management

I = 300L2 where L is flame length (m)

Radiation IntensityRadiation Intensity

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0

10

20

30

40

50

60

0 5000 10000 15000 20000Fire Intensity (kW/m)

Rad

iati

on

In

ten

sity

(k

W/m

2)

12

43

56 7

8

11

9

12

10

Distance fromflame front (m)

7

2.3

675/1.5m

16

3100/3.2m1200/2m

Canadian Wildland Fire Information Canadian Wildland Fire Information SystemSystem

• CWFIS creates fire weather and fire behaviour maps year-round, and hotspot maps throughout the season

http://cwfis.cfs.nrcan.gc.ca/en/index_e.php

Basic Wildland Fire Management

Fire Behaviour Warning SignalsFire Behaviour Warning Signals

• Watch out for:– Change in wind speed

and/or direction– Light fuels– Steep slopes– Change in slope and/or

aspect– Change in fuel type

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Advisories & WarningsAdvisories & Warnings

Basic Wildland Fire Management

• Fire Behaviour Advisory– Flame lengths >3.5m– Consider working flanks/rear

• Extreme Fire Behaviour Warning– Flame lengths >3.5m and

strengthening or changing winds

– Consider no action at all• Wind Advisory

– Conditions forecast to present hazards

Grasslands Fire Behaviour Grasslands Fire Behaviour PotentialPotential

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Grasslands Fire DangerGrasslands Fire Danger

• Degree of curing can drastically influence fire behaviour potential

• Fully cured grasses are particularly volatile

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Grasslands Fire Behaviour Pocket Grasslands Fire Behaviour Pocket CardCard

Basic Wildland Fire Management

Grasslands Fire Behaviour Pocket Grasslands Fire Behaviour Pocket CardCard

Basic Wildland Fire Management

Grasslands FirefightingGrasslands Firefighting

Basic Wildland Fire Management

ConclusionConclusion

• Fire Triangle consists of fuel, heat and oxygen• Fire Behaviour Triangle consists of fuel

characteristics, weather conditions and topography

• Canadian Forest Fire Danger Rating System provides relative index of fire risk in Canada

Basic Wildland Fire Management

ObjectivesObjectives

Upon completion of this section, you will be able to:1. Explain significance of cold fronts, thunderstorms

and upper ridge breakdowns on fire environment2. Describe 4 weather factors and their influence on

FB3. Describe 4 topographic factors and their influence

on FB4. Describe 4 fuel factors and their influence on FB5. Name 3 types of fire6. List parts of fire7. Describe 6 components of FWI System8. Recognize fire behaviour warning signals

Basic Wildland Fire Management