10-1-S290-EP Unit 10 Fuel Moisture Unit 10 Fuel Moisture

10-1-S290-EPUnit 10 Fuel Moisture

Unit 10Fuel Moisture


Unit 10 Objectives

1. Define critical live fuel moisture and the thresholds for various fuel types.

2. Identify three methods for obtaining live fuel moisture.

3. Describe the relationships between relative humidity, wind, and moisture content of fine and large fuels.


Unit 10 Objectives4. Explain how the amount and

duration of precipitation and soil moisture affect moisture content of fine and large fuels.

5. Define the fuel moisture timelag concept and its value to firefighters and fire managers.

6. Describe how fuel moisture is determined for dead fuels in each of the four timelag categories.


Unit 10 Objectives

7. Define moisture of extinction, how it varies in natural fuel complexes, and how it affects wildland fire ignition and spread.

8. Determine fuel moisture content for fine dead 1-hour timelag fuels from fuel moisture tables during daylight conditions.


When fuel moisture is high, fires ignite and burn poorly; when it is low, fires start easily, and spread and burn rapidly.

Fuel moisture will fluctuate with changes in weather, seasons, and topography.

10-5-S290-EP


Fuel Moisture

Fuel moisture content is the amount of water in a fuel expressed as a percent of

the oven dry weight of that fuel.

Wet Weight - Dry Weight

Dry Weight


Types of Fuel Moisture• LIVE fuel moisture:

– Found in living plants– Ranges from 30% to 300%– Varies over space, species and seasons

• DEAD fuel moisture:– Found in dead plants, forest litter, slash,

etc.– Ranges from 2% to 30%– Can change quickly over time and space


Fuel Moisture Affects Combustion• Before a fuel can burn, the moisture in it must

be converted to vapor through the heat process.

• The greater the moisture content, the higher the heat temperatures required to dry the fuel.

• The presence of moist fuel can affect the rate and direction that a wildland fire spreads.


Fuel moisture is one of the seven wildland environmental factors which must be continuously monitored for

safety reasons.


Critical Live Fuel Moisture and the Thresholds for

Various Fuel Types


Live Fuels

Herbaceous

Woody

Annuals

Perennials

Coniferous

Deciduous

• Different physiological properties

• Different chemical contents


Variations in Live Fuels• Change seasonally

• Differences based on species and fuel model

• Vary in relation to aspect, elevation

• Big picture influences:

– Drought, frost kill, insects, diseases


Annual Trend of Jack Pine Foliar Moisture

New Foliage

Old Foliage

March Oct

Month of Year

Mo

istu

re C

on

ten

t (p

erc

ent)

300

280

260

240

220

200

180

160

140

120

100

80

10-14-S290-EPUnit 10 Fuel Moisture 10-14-S290-EP


250

Moisture Content of CheatgrassMoisture Content of CheatgrassM

ois

ture

co

nte

nt

(per

cen

t)

Spring Summer

Coloration

gre

enp

urp

lest

raw

200

150

100

5030

0

10-15-S290-EP


Fuel Models with Live Fuels

• Herbaceous– FM 2 Timber with grass understory

• Woody– FM 4 Chaparral 6 ft.– FM 5 Brush 2 ft.– FM 7 Southern rough– FM 10 Timber with litter understory

10-17-S290-EPUnit 10 Fuel MoistureFuel Model 2

10-17-S290-EP


Fuel Model 4Fuel Model 4

10-18-S290-EP


Fuel Model 5

10-19-S290-EP


Fuel Model 7

10-20-S290-EP


Fuel Model 10


Rate of Spread Based on Live Fuel

Moisture


Crown Fires• Crown fires are live-fuels fires.• Can include large trees, but also the

canopies of shrubs (oak brush and manzanita).

• Need sufficiently low live fuel moisture to be a significant component to fire behavior.

• Need adequate dead fuels to initiate a crown fire.


Critical Live Fuel MoistureThe moisture content at which sustained, fast spreading, high intensity wildfires occur.

Gambel Oak 130% Sagebrush 100%Conifers 100%Manzanita 80%Chamise 60%


Three Methods for Obtaining Live Fuel Moisture


Live Fuel Moisture ContentStage of Vegetative Development Moisture Content

(Fireline Handbook, Appendix B)

Fresh foliage, annuals developing, early in growing cycle. Leaf-out, bud-break, early June.

300%

Maturing foliage, still developing with full turgorLate June.

Mature foliage, new growth complete and comparable to older perennial foliage. July to early August.

Entering dormancy, coloration starting, some leaves may have dropped from stem. Mid-August - September.

200%

100%

50%

<30%Completely cured. Treat as dead fuel.


Live Fuel Sampling• Collect relative sample from your area

of concern.

• Be sure to sample the fresh new growth of the year as well as the perennial older growth.

• Once collected, weigh it, dry it, weigh it again. Use formula.


On-line Data Sources


Relationships Between Relative Humidity, Wind, and

Moisture Content of Fine and Large Fuels


Moisture Balance

Water moves from higher concentrations to lower concentrations


PrecipitationDew

Ground moistureGround moisture

Moisture Exchange in Wildland Fuels

Moisture Exchange in Wildland Fuels

HumidityEvaporation

Evaporation

10-31-S290-EP


Equilibrium Moisture Content

• Occurs when there is no net loss or gain of moisture between fuels and the surrounding air.

• Moisture content attained when subjected to a constant temperature and humidity condition for an indefinite length of time.


Environmental Factors Influencing Fuel Moisture

ELEVATION

REALTIVEHUMIDITY

FUELMOISTURE

PRECIPITATION

WIND

INDIRECT INFLUENCES DIRECT INFLUENCES

TEMPERATURESHADED

UNSHADED

SOLARRADIATION

SLOPE

ASPECT

CANOPY

CLOUDS

NIGHT

10-33-S290-EP


Air Temperature

Fuel Moisture8%

3%

110o

85o 85o

Surface Temperature

160o

Shaded vs. Unshaded Effects on Fuel Moisture

10-34-S290-EP


Aspect Affects Fuel Moisture

Mo

istu

re c

on

ten

t (p

erce

nt) 15

10

5

0

0 0600 1200 1800Time of day

North slope

West slope

South slope

East slope


Elevation Affects Fuel Moisture (Daytime)

6000 feet

5000 feet

4000 feet

3000 feet

2000 feet

1000 feet

Temperature RH Fuel Moisture

69°

73°

76°

80°

83°

87°

39%

35%

31%

27%

25%

22%

8%

7%

6%

5%

5%

4%

Elevation

10-36-S290-EP


Slope Percent Affects Solar Heating

10-37-S290-EP


Wind Affects Fuel Moisture

10-38-S290-EP


Wind Affects Fuel MoistureWind can accelerate the rate at which a fuel reaches its moisture equilibrium.

– During calm air conditions, the air next to the fuels tends to become saturated with water vapor, decreasing the evaporation rate of moisture from the fuel.

– Wind removes this saturated air, continually replacing it with drier air and thus speeding up the evaporation process.


How the Amount and Duration of Precipitation and Soil Moisture

Affect Moisture Content ofFine and Large Fuels


Fine Dead Fuels• Fine, dead fuels

react very rapidly to precipitation.

• Additional rainfall has little effect on the fuels.

• Rainfall can be responsible for wetting the soils in contact with fuels.


Duration of Precipitation and Fuel Moisture

Fu

el M

ois

ture

Co

nte

nt

(per

cen

t)

Hours of continuous precipitation

1-hour 10-hour

100-hour

10-42-S290-EP


The Fuel Moisture Timelag Concept and its Value to

Firefighters and Fire Managers


Timelag is the time it takes dead fuel to reach 63% of the difference between its current moisture content and that it would reach at EMC (maintained at steady environmental conditions).

• Timelag is an indication of the rate fuel gains or loses moisture due to changes in its environment.

• It is expressed as the rate (hours) at which the fuel type approaches the moisture equilibrium of its surrounding atmosphere.


Timelag and Fuel Size Relationships

1006040

20

10

4

2

1

Tim

elag

(d

ays)

Branchwood diameter (inches)1.4 2 4 6 8 10

About 40 days


Reaction Time of Fuels to Wetting and Drying

Mo

istu

re c

on

ten

t 12” log

1/2” sticks

1 2 3 4 5 6 Day Lastbefore day of

Days after

Precipitation10-46-S290-EP


• A fuel complex of homogeneous

fuel is never seen.

• A pure grass stand comes closest to being a homogeneous fuel.


Dead Fuel Timelag Categories

1-hour timelag fuels: 0 to 1/4 diameter

10-hour timelag fuels: 1/4” to 1” diameter

100-hour timelag fuels: 1” to 3” diameter

1000-hour timelag fuels: 3” to 8” diameter






Daily Relationship of Relative Humidity to Fine Dead Fuel Moisture

Relative humidity

Moisture content

RH

& m

ois

ture

per

cen

t

012PM 6AM NOON 6PM 12PM


How Fuel Moisture is Determined for Dead Fuels

in Each of the FourTimelag Categories


Determining Dead Fuel Moisture

1-hour• Calculate from fuel moisture charts• NFDRS outputs• Measure - drying

oven and scales

10-hour• Fuel moisture sticks• NFDRS outputs• Measure - drying

oven and scales


Determining Dead Fuel Moisture

100-hour• NFDRS outputs• Measure - drying oven and scales• Calibrated moisture meter

1000-hour• NFDRS outputs• Measure - drying oven and scales• Calibrated moisture meter


Moisture of Extinction:

How it Varies in Natural Fuel Complexes and How it Affects

Wildland Fire Ignition and Spread


Moisture of Extinction

• Fuel moisture content at which a fire will not spread or spreads only sporadically and in a non-predictable manner.

• Dependent upon:– Fuel loading– Size and shape– Arrangement– Chemical content

10-58-S290-EP



Fuel Model 1 - Short grass ...........12%

Fuel Model 2 - Timber .................15%

Fuel Model 3 - Tall grass ..............25%

Fuel Model 4 - Chaparral ..............20%

Fuel Model 5 - Brush ....................20%

Fuel Model 6 - Dormant brush ......25%

Fuel Model 7 - Southern Rough ....40%



Fuel Model 8 - Closed timber litter ......30%

Fuel Model 9 - Hardwood litter............25%

Fuel Model 10 - Timber ..............….....25%

Fuel Model 11 - Light slash ................15%

Fuel Model 12 - Medium slash ............20%

Fuel Model 13 - Heavy slash ...............25%


Determining Fuel Moisture Content in Fine Dead Fuels

(1-hour timelag)

Dry Bulb TemperatureRelative Humidity

Reference FuelMoisture (RFM)

MonthShaded or UnshadedTime of DaySite LocationAspectSlope

Fuel Moisture Correction Value (FMC)

+

=

Adjusted Fine DeadFuel Moisture (FDFM)

10-61-S290-EP


Fine Dead Fuel Moisture Worksheet

10-62-S290-EP


Table 2Reference Fuel Moisture

(daytime 0800-1959)Input Line 6

Go to Tables 3, 4, or 5 for corrections.

10-63-S290-EP


Table 3Fine Dead Fuel Moisture Content

Corrections (daytime 0800-1959) May, June, JulyInput Line 13

Note: B = 1,000 to 2,000 feet below siteL = + 1,000 feet of site location

A = 1,000 to 2,000 feet above site10-64-S290-EP



Corrections(daytime 0800-1959) Feb.-Apr., Aug.-Oct.

Input Line 13

10-65-S290-EP


A = 1,000 to 2,000 feet above site



Corrections(daytime 0800-1959) November, December, January

Input Line 13

10-66-S290-EP


A = 1,000 to 2,000 feet above site


Temperature & Humidity Selection

2,000 feet

1,000 feet

0 feet

1,000 feet

2,000 feet

Above Site (A)

Below Site (B)

Site Location (L)

New T°/RH%Prediction

New T°/RH%Prediction

T°/RH% PredictionNo adjustment needed


Dry Bulb 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95Temperature (degrees F) 4 9 14 19 24 29 34 39 44 49 54 59 64 69 74 79 84 89 94 99

10 - 29 1 2 2 3 4 5 5 6 7 8 8 8 9 9 10 11 12 12 13 13 14 30 - 49 1 2 2 3 4 5 5 6 7 7 7 8 9 9 10 10 11 12 13 13 13 50 - 69 1 2 2 3 4 5 5 6 6 7 7 8 8 9 9 10 11 12 12 12 13 70 - 89 1 1 2 2 3 4 5 5 6 7 7 8 8 8 9 10 10 11 12 12 13 90 - 109 1 1 2 2 3 4 4 5 6 7 7 8 8 8 9 10 10 11 12 12 13 109 + 1 1 2 2 3 4 4 5 6 7 7 8 8 8 9 10 10 11 12 12 12

100

RELATIVE HUMIDITY (PERCENT)

Example: Dry Bulb temp: 85o

Relative Humidity: 22RFM: 3

Table 2REFERENCE FUEL MOISTURE DAY (0800-1959)

Input Line 6

10-68-S290-EP


Fine Dead Fuel Moisture WorksheetINPUT

0 Projection Point1 Day Time Calculation D D D2 Dry Bulb Temperature, oF3 Wet Bulb Temperature, oF4 Dew Point, oF5 Relative Humidity, %6 Reference Fuel Moisture (RFM, %

(From Table 1)7 Month8 Unshaded (U) or Shaded (S) (Circle) U/ S U/ S U/ S9 Time10 Elevation Change B/ L/ A B/ L/ A B/ L/ A

B=1,000 to 2,000 feet below siteL=+/ - 1,000 feet of site locationA=1,000 to 2,000 feet above site

11 Aspect (N,S,E,W)12 Slope %13 Fuel Moisture Correction (FMC), %

(From Table 3, 4, or 5)

OUPUT1 Fine Dead Fuel Moisture (FDFM), %

(Line 6 + line 13)

85

22 3

60

62 8

10-69-S290-EP


Aspect % SlopeB L A B L A B L A B L A B L A B L A

N 0-30 3 4 5 1 2 3 1 1 2 1 1 2 1 2 3 3 4 531+ 3 4 5 3 3 4 2 3 4 2 3 4 3 3 4 3 4 5

E 0-30 3 4 5 1 2 3 1 1 1 1 1 2 1 2 4 3 4 531+ 3 4 4 1 1 1 1 1 1 1 2 3 3 4 5 4 5 6

S 0-30 3 4 5 1 2 2 1 1 1 1 1 1 1 2 3 3 4 531+ 3 4 5 1 2 2 0 1 1 0 1 1 1 2 2 3 4 5

W 0-30 3 4 5 1 2 3 1 1 1 1 1 1 1 2 3 3 4 531+ 4 5 6 3 4 4 1 3 3 1 1 1 1 1 1 3 3 4

N all 4 5 6 4 5 5 3 4 5 3 4 5 4 5 5 4 5 6E all 4 5 6 3 4 5 3 4 5 3 4 5 4 5 6 4 5 6S all 4 5 6 3 4 5 3 4 5 3 4 5 3 4 5 4 5 6W all 4 5 6 4 5 5 3 4 5 3 4 5 3 4 5 4 5 6

1600> 1800>

SHADED - 50% OR MORE SHADING OF SURFACE FUELS

UNSHADED - LESS THAN 50% SHADING OF SURFACE FUELS0800> 1000> 1200> 1400>

Example:Month: August 20S/U: ShadedTime: 1200Elevation: Mid-slopeAspect: EastSlope: -- FMC%: 4%

Table 4 – Fine Dead Fuel MoistureContent Corrections, Day (0800-1759)

February, March, April, August, September, October

10-70-S290-EP


INPUT







(Line 6 + line 13)

Aug

1200

E--

4

May

1400

S200

Fine Dead Fuel Moisture Worksheet

10-71-S290-EP


Dry Bulb 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95Temperature (degrees F) 4 9 14 19 24 29 34 39 44 49 54 59 64 69 74 79 84 89 94 99

10 - 29 1 2 2 3 4 5 5 6 7 8 8 8 9 9 10 11 12 12 13 13 14 30 - 49 1 2 2 3 4 5 5 6 7 7 7 8 9 9 10 10 11 12 13 13 13 50 - 69 1 2 2 3 4 5 5 6 6 7 7 8 8 9 9 10 11 12 12 12 13 70 - 89 1 1 2 2 3 4 5 5 6 7 7 8 8 8 9 10 10 11 12 12 13 90 - 109 1 1 2 2 3 4 4 5 6 7 7 8 8 8 9 10 10 11 12 12 13 109 + 1 1 2 2 3 4 4 5 6 7 7 8 8 8 9 10 10 11 12 12 12

100

RELATIVE HUMIDITY (PERCENT)

Table 2REFERENCE FUEL MOISTURE DAY (0800-1959)

Input Line 6

Example: Dry Bulb temp: 92o

Relative Humidity: 16RFM: 2

10-72-S290-EP


Aspect % SlopeB L A B L A B L A B L A B L A B L A

N 0-30 4 5 6 3 4 5 2 3 4 2 3 4 3 4 5 4 5 631+ 4 5 6 4 5 6 4 5 6 4 5 6 4 5 6 4 5 6

E 0-30 4 5 6 3 4 4 2 3 3 2 3 3 3 4 5 4 5 631+ 4 5 6 2 3 4 2 2 3 3 4 4 4 5 6 4 5 6

S 0-30 4 5 6 3 4 5 2 3 3 2 2 3 3 4 4 4 5 631+ 4 5 6 2 3 3 1 1 2 1 1 2 2 3 3 4 5 6

W 0-30 4 5 6 3 4 5 2 3 3 2 3 3 3 4 4 4 5 631+ 4 5 6 4 5 6 3 4 4 2 2 3 2 3 4 4 5 6

N all 4 5 6 4 5 6 4 5 6 4 5 6 4 5 6 4 5 6E all 4 5 6 4 5 6 4 5 6 4 5 6 4 5 6 4 5 6S all 4 5 6 4 5 6 4 5 6 4 5 6 4 5 6 4 5 6W all 4 5 6 4 5 6 4 5 6 4 5 6 4 5 6 4 5 6

1600> 1800>

SHADED - 50% OR MORE SHADING OF SURFACE FUELS

UNSHADED - LESS THAN 50% SHADING OF SURFACE FUELS0800> 1000> 1200> 1400>

Table 5 – Fine Dead Fuel MoistureContent Corrections, Day (0800-1759)

November, December, January

B = 1000 to 2000 feet below site locationL = +/- 1000 feet of site locationA = 1000 to 2000 feet above site location

Example:Month: NovemberS/U: UnshadedTime: 1500Elevation: 1500 AboveAspect: WestSlope: 40% FMC%: 3%

10-73-S290-EP


INPUT







(Line 6 + line 13)

92------16 2

Nov

1500

W40 3

5

Solution to Question 3.a.

3a

10-74-S290-EP


INPUT







(Line 6 + line 13)

75------28 4

Oct

1700

N20 4

8

Solution to Question 3.b.

3b

10-75-S290-EP


INPUT







(Line 6 + line 13)

1600

N20 2

5

Solution to Question 3.b.

1600 1600

Aug Aug Aug

80 8080

20 20203 3 3

B L A

N N20 20

3 1

64

10-76-S290-EP


Severe Fire Behavior Potential Related to Relative Humidity and Fuel Moisture Content

(For Western US only)

10-77-S290-EP


Review Unit 10 Objectives

1. Define critical live fuel moisture and the thresholds for various fuel types.

2. Identify three methods for obtaining live fuel moisture.

3. Describe the relationships between relative humidity, wind, and moisture content of fine and large fuels.


Review Unit 10 Objectives4. Explain how the amount and

duration of precipitation and soil moisture affect moisture content of fine and large fuels.

5. Define the fuel moisture timelag concept and its value to firefighters and fire managers.

6. Describe how fuel moisture is determined for dead fuels in each of the four timelag categories.


Review Unit 10 Objectives

7. Define moisture of extinction, how it varies in natural fuel complexes, and how it affects wildland fire ignition and spread.

8. Determine fuel moisture content for fine dead 1-hour timelag fuels from fuel moisture tables during daylight conditions.

Documents

10-1-S290-EP Unit 10 Fuel Moisture Unit 10 Fuel Moisture