Surface Fuel Model Descriptions

Surface Fuel Models

Fuel Model

Description

Grass Fuel Type Models (nearly pure grass and/or forb type)

GR1 (101)

Sparse grass, though small amounts of fine dead fuel may be present. The grass in GR1 is generally short, either naturally or by grazing, and may be sparse or discontinuous.

GR2 (102)

Grass, though small amounts of fine dead fuel may be present. Load is greater than GR1, and fuelbed may be more continuous. Shrubs, if present, do not affect fire behavior.

GR3 (103)

Continuous, coarse, humid-climate grass. Grass and herb fuel load is relatively light; fuelbed depth is about 2 feet. Shrubs are not present in significant quantity to affect fire behavior.

GR4 (104)

Continuous, dry-climate grass. Load and depth are greater than GR2; fuelbed depth is about 2 feet.

GR5 (105)

Humid-climate grass. Load is greater than GR3 but depth is lower, about 1 to 2 feet.

GR6 (106)

Continuous humid-climate grass. Load is greater than GR5 but depth is about the same. Grass is less coarse than GR5.

GR7 (107)

Continuous dry-climate grass. Load and depth are greater than GR4. Grass is about 3 feet tall.

GR8 (108)

Continuous, very coarse, humid climate grass. Load and depth are greater than GR6. Spread rate and flame length can be extreme if grass is fully cured.

GR9 (109)

Dense, tall, humid-climate grass. Load and depth are greater than GR8, about 6 feet tall. Spread rate and flame length can be extreme if grass is fully or mostly cured.

Grass-Shrub Fuel Type Models (mixture of grass and shrub, up to 50 percent shrub coverage)

GS1 (121)

Grass and shrubs combined. Shrubs are about 1 foot high, grass load is low. Spread rate is moderate; flame length low. Moisture of extinction is low.

GS2 (122)

Grass and shrubs combined. Shrubs are about 1 foot high, grass load is low. Spread rate is moderate; flame length low. Moisture of extinction is low.

GS3 (123)

Grass and shrubs combined. Moderate grass/shrub load, average grass/shrub depth less than 2 feet. Spread rate is high; flame length moderate. Moisture of extinction is high.

GS4 (124)

Grass and shrubs combined. Heavy grass/shrub load, depth greater than 2 feet. Spread rate high; flame length very high.

Shrub Fuel Type Models (Shrubs cover at least 50 percent of the site, grass sparse to nonexistent)

SH1 (141)

Woody shrubs and shrub litter. Low shrub fuel load, fuelbed depth about 1 foot; some grass may be present. Spread rate is very low; flame length very low.

SH2 (142)

Woody shrubs and shrub litter. Moderate fuel load (higher than SH1), depth about 1 foot, no grass fuel present. Spread rate is low; flame length low.

SH3 (143)

Woody shrubs and shrub litter. Moderate shrub load, possibly with pine overstory or herbaceous fuel, fuel bed depth 2 to 3 feet. Spread rate is low; flame length low.

SH4 (144)

Woody shrubs and shrub litter. Low to moderate shrub and litter load, possibly with pine overstory, fuel bed depth about 3 feet. Spread rate is high; flame length moderate.

SH5 (145)

Woody shrubs and shrub litter. Heavy shrub load, depth 4-6 feet. Spread rate very high; flame length very high. Moisture of extinction is high.

SH6 (146)

Woody shrubs and shrub litter. Dense shrubs, little or no herbaceous fuel, fuelbed depth about 2 feet. Spread rate is high; flame length high.

SH7 (147)

Woody shrubs and shrub litter. Very heavy shrub load, depth 4 to 6 feet. Spread rate lower than SH7, but flame length similar. Spread rate is high; flame length very high.

SH8 (148)

Woody shrubs and shrub litter. Dense shrubs, little or no herbaceous fuel, fuelbed depth about 3 feet. Spread rate is high; flame length high.

SH9 (149)

Woody shrubs and shrub litter. Dense, finely branched shrubs with significant fine dead fuel, about 4 to 6 feet tall; some herbaceous fuel may be present. Spread rate is high, flame length very high.

Timber-Understory Fuel Type Models (Grass or shrubs mixed with litter from forest canopy)

TU1 (161)

Low load of grass and/or shrub with litter. Spread rate is low; flame length low.

TU2 (162)

Moderate litter load with shrub component. High extinction moisture. Spread rate is moderate; flame length low.

TU3 (163)

Moderate forest litter with grass and shrub components. Extinction moisture is high. Spread rate is high; flame length moderate.

TU4 (164)

Short conifer trees with grass or moss understory. Spread rate is moderate; flame length moderate.

TU5 (165)

Heavy forest litter with a shrub or small tree understory. Spread rate is moderate; flame length moderate.

TUML (171)

Timber Understory Dynamic ML (TSYL 2022)

TUML2 (172)

TUML2 - Low-Moderate Fuel Load Timber Understory Dynamic ML (TSYL 2022)

Timber Litter Fuel Type Models (dead and down woody fuel litter beneath a forest canopy)

TL1 (181)

Compact forest litter. Light to moderate load, fuels 1 to 2 inches deep. May be used to represent a recently burned forest. Spread rate is very low; flame length very low.

TL2 (182)

Broadleaf (hardwood) litter. Low load, compact broadleaf litter. Spread rate is very low; flame length very low.

TL3 (183)

Moderate load conifer litter, light load of coarse fuels. Spread rate is very low; flame length low.

TL4 (184)

Moderate load of fine litter and coarse fuels. Includes small diameter downed logs. Spread rate is low; flame length low.

TL5 (185)

High load conifer litter; light slash or mortality fuel. Spread rate is low; flame length low.

TL6 (186)

Moderate load broadleaf litter, less compact than TL2. Spread rate is moderate; flame length low.

TL7 (187)

Heavy load forest litter, includes larger diameter downed logs. Spread rate low; flame length low.

TL8 (188)

Moderate load long-needle pine litter, may include small amount of herbaceous load. Spread rate is moderate; flame length low.

TL9 (189)

Very high load, fluffy broadleaf litter. TL9 can also be used to represent heavy needle-drape. Spread rate is moderate; flame length moderate.

TLML1 (191)

Timber Litter ML (TSYL 2022)

Slash-Blowdown Fuel Type Models (activity fuel/slash or debris from wind damage)

SB1 (201)

Light dead and down activity fuel.  Fine fuel load is 10 to 20 t/ac, weighted toward fuels 1 to 3 inches diameter class, depth is less than 1 foot. Spread rate is moderate; flame length low.

SB2 (202)

Moderate dead and down activity fuel or light blowdown. Fine fuel load is 7 to 12 t/ac, evenly distributed across 0 to 0.25, 0.25 to 1, and 1 to 3 inch diameter classes, depth is about 1 foot. Blowdown is scattered, with many trees still standing. Spread rate is moderate; flame length moderate.

SB3 (203)

Heavy dead and down activity fuel or moderate blowdown. Fine fuel load is 7 to 12 t/ac, weighted toward 0 to 0.25 inch diameter class, depth is more than 1 foot. Blowdown is moderate; trees compacted to near the ground. Spread rate is high; flame length high.

SB4 (204)

Heavy blowdown fuel. Blowdown is total, fuelbed not compacted, most foliage and fine fuel still attached to blowdown. Spread rate very high; flame length very high.

Non-burnable Fuel Type Models (insufficient wildland fuel to carry a wildland fire under any condition)

NB1 (91)

Urban

NB2 (92)

Snow/Ice

NB3 (93)

Agricultural

NB8 (98)

Open Water

NB9 (99)

Bare Ground

 Land Use Classification for Fire Encroachment

Land Use Classification

Description

Urban Classes based on WUI Density and Fire Behavior of the Surrounding Fuels Load Type (Originally NB91 Urban)

UIL (911)

Isolated urban surrounded by Low FB fuel

USL (912)

Scattered urban surrounded by Low FB fuel

UCL (913)

Urban core surrounded by Low FB fuel

UIH (914)

Isolated urban surrounded by High FB fuel

USH (915)

Scattered urban surrounded by High FB fuel

UCH (916)

Urban core surrounded by High FB fuel

UNB (919)

Non-burnable Urban areas

Agricultural Classes based on Seasonal Changes and Fuel Load (Originally NB93, Agricultural Non-Burnable)

ASL (931)

Agricultural Low Load Fuels with seasonal changes of its Burnable condition

ASH (932)

Agricultural High Load Fuels with seasonal changes of its Burnable condition

AGC (938)

Golf courses - Non-Burnable (no encroachment)

ANB (939)

Agricultural Fields maintained in a Non-Burnable condition

Road Classes based on Road Category and Surrounding Fuels

RNL (941)

Minor roads surrounded by Low FB fuel

RNH (942)

Minor roads surrounded by High FB fuel

RML (943)

Major roads surrounded by Low FB fuel

RMH (944)

Major roads surrounded by High FB fuel

RNB (949)

Roads surrounded by non-burnable fuels

Water Classes based on Water Body Type and Surrounding Fuels (Originally NB98, Water)

WNL (981)

Minor Water streams surrounded by Low Load Fuel (moderate encroachment)

WNH (982)

Minor Water streams surrounded by High Load Fuel (high encroachment)

WML (983)

Major Water streams surrounded by Low Load Fuel (moderate encroachment)

WMH (984)

Major Water streams surrounded by High Load  Fuel (high encroachment)

WBD (989)

Water Bodies