Transcript Fire Ecology and Management Why is this course important?

Photo: The Daily Galaxy

CPBM Objectives (chapter 8)
1) Identify fire behavior terms
2) Explain the fire triangle
3) Discuss the major elements of the fire
environment
4) List and explain the three methods of heat
transfer
5) List fuel characteristics which govern
combustion

CPBM Objectives (chapter 8)
6) Identify Fuel Models and examples in Florida
7) Explain the difference between fire intensity and
severity and how both can be regulated and
measured
8) Define residence time and why it is significant in
Rx fire
9) Discuss indicators of erratic or potentially erratic
fire behavior
SPOT FIRE
UNBURNED
ISLAND

Surface Fire
 Burning in surface fuels
▪ Grass, shrubs, litter

Ground Fire
 Smoldering in ground fuels
▪ duff, peat, roots, stumps

Photo: Univ. of Toronto Fier Lab
Crown Fire
 Burning in aerial fuels
▪ Crowns or canopy of the overstory
▪ May or may not be independent of surface fire
Photo: News Provider
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Spotting – burning or glowing embers
being transported in the air.
Torching – Movement of fire from the
surface to the crowns of individual
trees.
Flare Up – A sudden increase in ROS
and Intensity.
Energy release in the form of heat and light when oxygen combines with a
combustible material (fuel) at a suitably high temperature
The Fire Triangle
Fuel
Oxygen
Heat
Photosynthesis: converts radiant energy to stored
chemical energy (CO2 + H2O ---light-----> C6H12O6 + O2).
 Combustion: reverses photosynthesis

(C6H12O6 + O2 ---high temperature-----> H2O + CO2 + heat and light)
(fuel)
(325 C for wood)
 Same process as decay and decomposition
 Begins with endothermic reaction, becomes exothermic
 Produces thermal, radiant and kinetic energy

Extinction: insufficient heat to sustain combustion
4 Phases of Combustion
Pre-Ignition
Flaming
Smoldering Glowing

Pre-ignition
 Requires heat/energy input to
increase surface temperature >200˚C
 Dehydration
 Volatilization of waxes, oils, other
extractives
 Pyrolysis (chemical decomposition of
organic matter without Oxygen– inside fuels,
emits volatiles)
 Volatiles either condense into
particles (smoke) or are consumed
during flaming combustion
Pre-Ignition

Ignition
 Transition to flaming
combustion: gases
released by pyrolysis
ignite
 Surface temperatures
around 320 C (600F)
 Heat released by
combustion brings other
fuels to ignition

Flaming combustion
 Surface temperatures 200- 500˚ C
 Combustible volatiles ignite above
surface, creating flame: the GASES
are burning, not the fuel itself.
 Combustion occurs in zone above
fuel surface
 Oxidation produces: heat, CO2, H2O
and incompletely degraded organic
compounds
 Smoke includes these + other gases
which condense or reform above
flame zone
Flaming

Smoldering
 No visible flames
 Surface temperatures < 500 C
 Carbon buildup on surface reduces gas

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

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production that would maintain flame
Occurs when fuels tightly packed
Surface char oxidizes to CO2, H2O, ash
Continued oxidation of other compounds
Smoldering duff and ground fires raise soil
temperature and can kill roots
Large quantities of smoke
Smoldering


A result of incomplete combustion
Major constituents
 Particulate matter
▪ Solid or liquid particle suspended in
atmosphere
▪ Condensed hydrocarbons and tar
materials
▪ Entrained fragments of vegetation and ash
 CO2 and CO
 H2O
 Gaseous hydrocarbons

Smoke/volume burned increases for:
 Low intensity fires in moist or living fuels
 High rates of spread (& less efficient
combustion)
Glowing
•All volatiles have already been driven off, oxygen reaches the
combustion surfaces, and there is no visible smoke (products are CO2
and CO)
•Oxidation of solid fuel accompanied by incandescence
•This phase follows smoldering combustion, continues until
temperature drops or only non-combustible ash remains
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Radiation
 Radiation
 For example, the sun, and your hand…
 For example, the sun, and your hand…
 Electromagnetic waves transfer heat to fuel surface
 Electromagnetic waves transfer heat to fuel
only
surface only
 Accounts for most drying and heating of fuel
surfaces
of flame
on opposite
 Accounts
forahead
most drying
andorheating
of fuelsteep
surfaces
slopes–
radiates
all directions
ahead
of flame
or onin
opposite
steep slopes– radiates
in all directions

Convection
 Convection
 Vertical (or other direction) movement of gas or
liquid,
Vertical
(or other
as heat
rises direction) movement of gas or
liquid, as heat rises
 Heats plant foliage above surface fires and fuels
ahead
Heatsofplant
foliage
surfaceorfires
and fuels
the flame
onabove
steep slopes,
if wind
ahead of the flame on steep slopes, or if wind
driven
driven
 Carries firebrands away from fire; spotting
potential
Carries firebrands away from fire; spotting
potential
 Can create enormous columns and drive fire
behavior
Can create enormous columns and drive fire
behavior
Heat Transfer Processes

Conduction
Transfer by molecular activity within a solid
object
 Primary method for raising temperatures
within large fuels
 Occurs between objects/fuels that are in
contact
 Transfers heat in dense fuels, requiring
additional heat to reach ignition

Rate of spread (ROS): rate at which fire front
advances through forest fuel (ft/sec, chains/min)
 Residency Time: Duration for flaming combustion
to pass a specific location.

Residency Time = Flame Depth/ROS

Flame Length & Depth

Intensity – rate of heat energy during combustion
 Reaction intensity: per unit area (BTU·ft-2·min-1)
 Fireline Intensity: per unit length of the fire front
(BTU·ft-1·min-1)
I = h·w·r
I
h
w
r
fireline intensity
fuel heat content
weight of fuel consumed per unit area
rate of spread
*Flame Length is a good estimate of intensity
Severity: Impact of fire on the environment
 Plants, animals, soils, water
HIGH
Backing fire in
long unburned
longleaf pine
Stand replacing
fire in mixed
conifer forests
SEVERITY

Head fire in
frequently
burned
longleaf pine
LOW
LOW
Chaparral
Brush Fires
INTENSITY
HIGH
1. Weather
2. Fuels
3. Topography

Surface Fuels
 Grasses
 Shrubs
 Litter (leaves)
 Woody debris

Ground Fuels
litter
 Duff (partially decomposed)
 Peat
 Roots
 Stumps
Duff
fermentation layer
humus
mineral soil

Aerial Fuels
 Crown or canopy of
overstory

Ladder Fuels (located between
crown and surface fuels)
 Smaller trees
 Vines

Size and Shape
 Surface area:volume ratio
▪ Grasses
1000:1
▪ Palmetto
▪ Branches
▪ Logs
40:1

Particle Density

Heat Content (stored energy)
 6,000-12,000 BTU/lb

Fuel Chemistry
 Volatile oils

Mineral Content
 Dampening effect on
combustion

Fuel Arrangement
 Vertical
▪ Grasses & shrubs
 Horizontal
▪ Litter
▪ Downed woody debris

Fuel Loading
 By size classes
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ALL FUELBED PROPERTIES
Compactness
 Bulk density (fuel load/fuelbed volume)
 Packing ratio (fuelbed density/particle density)
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Continuity
 Vertical
 Horizontal

Fuel Moisture Content (FMC)
 Large dampening effect on combustion
 Heat sink
Fuel Moisture Content (%) = (Water Weight / Dry Fuel Weight) x 100
▪ FMC changes hourly, daily, and seasonally!

What influences FMC
 In Dead Fuels
▪ Precipitation (amount and
duration)
▪ Temperature
▪ Relative humidity
▪ Wind

Equilibrium Moisture Content
 For a given temperature and RH dead fuel will
reach a FMC at equilibrium.
 Environmental conditions are not constant
 Fuel is constantly changes FMC to reach EMC
 The lag time to reach EMC depends on particle
size

Timelag categories for dead woody fuels
Timelag Class
Fuel Diameter
Timelag Range (hr)
1 Hour
0-1/4”
0-2
10 Hour
¼”-1”
2-20
100 Hour
1-3”
20-200
1000 Hour
3-8”
200-2000
Timelag, or “response time”, is the time it takes for 63% of the change
to occur between one EMC and a second EMC when a fuel in
equilibrium with a stable environmental condition is suddenly exposed
to a different stable environmental condition.
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Small diameter fuels react quickly to
hourly and daily changes.
 Important to monitor.
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Large diameter fuels react more to
seasonal changes
 California versus Florida?
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Fine fuels drive fire behavior
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Moisture of Extinction
 Dead: 12-40%
 Live: >120%

Available Fuel

Florida Fine Fuel Moisture Calculation Chart
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http://www.fldof.com/wildfire/rx_training.html#cbc
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Live Fuels
 FMC can be much higher than dead fuels
(100-300%)
 Influenced by:
▪ Drought (KBDI)
▪ RH
▪ Wind
*Ignition of live fuels may largely depend the combustion
characteristics of other fuels (e.g. dead surface fuels).

Duff Moisture
 Very dry to very moist
 <30% FMC duff can burn on its own
 Potential for tree mortality in burning long
unburned forests
 May smolder for long durations
 May cause lots of smoke
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FMC
Wind
wind
convection
 Increases O2
radiation
 Bends flames
 Increases ROS
 Dries fuels
conduction

Slopes
 Similar effect as wind
 Bends flames
 ROS higher upslope
Slope Position
top, middle, bottom
Aspect

Other topographic
features
 Valleys
 Box Canyons
 Steep draws
 Elevation
ELEVATION
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Indicators (on a Rx burn)
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KBDI>500
FMC (fine) <7%
RH<30%
Cold front approaching
Gusty winds
Dust devils/fire whirls
Just inland from seabreeze
Well-defined convection column
Thunderstorms
Spotting
DI approaching 70

Fire Behavior Prediction
Models (e.g. BehavePlus)
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INPUTS
Fuel characteristics
FMC
Slope
Wind
OUTPUTS
Rate of Spread
Fireline Intensity
Flame Lengths
and more…