Glossary of Fire Terms

Backing fire: Fire that is moving into the wind (See heading and flanking fire).

Backfiring: Intentionally setting fire to fuels inside a control line to contain a fire.

Blackline: Refers to fuels that have burned, either intentionally or not. Many prescribed fire and wildfire suppression techniques are based on the concept of blackline as a barrier to fire spread.



Catface: General term used to describe the triangular wound found at the base of a tree and often caused by fire. From one to many fire scar lesions caused by individual fire events can be found within the catface.

Chain: A traditional forestry term equal to 66' or approximately 20 m.

Composite Fire Chronology: (See Master Fire Chronology)

Conduction: The movement of heat from one molecule to another.

Convection: The movement heat by currents in liquids or gases.

Creeping fire: A low intensity fire with a negligible rate of spread.


Crown Fire: Fire that has ascended from the ground into the forest canopy.

Drip Torch: An ignition tool which drips a mixture flaming diesel and gasoline onto the ground.

Fine Fuels:


Fire Behavior:The manner in which a fire reacts to fuel, weather, and topography. Common terms used to describe behavior include: smoldering, creeping, running, spotting, torching, and crowning.

Fire Cycle:

1) A fire-return interval calculated using a negative exponential (or Weibull) distribution, applied using current age-class structure on the landcape.
2) Length of time required to burn an area equal in size to a specified area.

Fire Ecology:

Fire Effects:

Fire Event: A single fire or series of fires within an area at a particular time.

Fire-Free Interval: Time between two successive fire events at a given site or an area of a specified size.

Fire Frequency: The return interval or recurrence interval of fire in a given area over a specific time.

Fire Intensity Energy release per unit length of flame front.

Fire Interval: (see Fire-Return Interval)

Fire Management

Fire Occurrence (or fire incidence):

Fire Periodicity:

Fire Predictability: A measure of variation in fire frequency expressed as a range, standard deviation, or standard error.

Fire Regime: The combination of fire frequency, predictability, intensity, seasonality, and size characteristics of fire in a particular ecosystem.

Fire Resistant Tree:

Fire-Return Interval: The number of years between two successive fire events at a specific site or an area of a specified size.

Fire Rotation: The length of time necessary to burn an area the size of a specific area (for example a watershed).

Fire Scar Susceptible Tree:

Fire Sensitive Tree:

Fire Severity: The effect of fire on plants. It is dependant on intensity and residence dependant of the burn. An intense fire may not necessarily be severe. For trees, severity is often measured as percentage of basal area removed.

Fireline Intensity: The rate of heat release along a unit length of fireline, measured in kW m-1.


Flame Length: The average length of the flame front from the ground to the flame tips.


Flanking Fire: Fire that is moving perpendicular to the wind (See heading and backing fire).

Foehn Wind: A dry wind associated with windflow down the lee side of a plateau or mountain range and with adiabatic warming (also called Santa Ana [southern California], Mono or North Wind [N. and central California], East Wind [western Washington and Oregon] or Chinooks [east side of Rockies] in other regions).


Description Material Diameter
Fine Needles, leaves, etc...
1 Hour Woody material, generally drying out within 1 hour. <1/4"
10 Hour Woody material, generally drying out within 10 hours. 1/4"-1"
100 Hour Woody material, generally drying out within 4 days. 1-3"
1000 Hour Woody material, generally drying out within 40 days. 3"+
Downed Fuel on the ground
Heavy Large logs and snags

Fuel Load: The amount of available and potentially combustible material, usually expressed as tons/acre.

Fuel Model: A standardized description of fuels available to a fire based on the amount, distribution and continuity of vegetation and wood.

Fuel Moisture: The amount of water in a fuel sample. The proportion of water to dry material. Percent fuel moisture = (Wet weight - Dry weight)/Dry weight * 100. Fire behavior is dependent, to a large extent, on how much water is in the fuel.

Ground Fire (or surface fire):-- Fire burning on the ground or through the understory and not reaching into the canopy.

Heading Fire: Fire that is moving with the wind (See backing and flanking fire).

Heavy Fuels:

High-Severity Burn:

Human-Caused Fire:

Ladder Fuels: Fuels, such as branches, shrubs or an understory layer of trees, which allow a fire to spread from the ground to the canopy.

Light-Severity Burn:


Mass Transfer: The movement of heat by burning firebrands, as used in the fire literature.

Master Fire Chronology: A chronology of all documented fire dates in designated area determined by crossdating.

Mean Fire-Return Interval (or mean fire-free interval, or mean fire interval: Arithmetic average of all fire-return intervals for a specific site for a specific interval of time.

Moderate-Severity Burn:

Natural Fire

Prescribed Fire: (also called prescribed or controlled burn) A fire ignited under known conditions of fuel, weather, and topography to achieve specific objectives.

Prescribed Natural Fire

Prescription A statement or plan specifying management objectives to be obtained, and air temperature, humidity, season, wind direction and speed, fuel and soil moisture conditions under which a fire will be started or allowed to burn.

Relative Humidity: The ratio of water vapor in the air to the maximum amount of vapor the air can hold at a given temperature and pressure. Fire behavior is dependent on, and can be predicted from, relative humidity.

Rate of Spread: The speed a fire travels, generally expressed as chains/hour.


Stand-Replacing Fire:

Spot Fire: A smaller fire that has started from sparks and brands thrown in the air by the main fire.

Spotting: Mass transfer of firebrands ahead of a fire front.

Surface Fire: A fire burning along the surface without significant movement into the understory or overstory, with flame length usually below 1 m.

Timelag Class: A method of categorizing fuels by the rate at which they are capable of moisture gain or loss, indexed by size class (see fuel definition).

Torching Fire: Fire burning principally as a surface fire that intermittently ignites the crowns of trees or shrubs as it advances.

Understory Fire: A fire burning in the understory, more intense than a surface fire with flame lengths of 1-3 m.

Urban-Rural Interface: (See Wildland-Urban Interface)

Vegetation Type: A standardized description of the vegetation in which a fire is burning. The type is based on the dominant plant species and the age of the forest and indicates how moist a site may be and how much fuel is likely to be present.

Water Repellency: The resistance to soil wettability, which can be increased by intense fires.

WFRB: Wild Fire for Resource Benefit.

Weibull Distribution:

Wildfire: A fire, naturally caused or caused by humans, that is not meeting land management objectives.

Wildland-Urban Interface: Zone where structures and other human developments meet, or intermingle with, undeveloped wildlands.

Definitions on this page have been obtained from a variety of sources. They include:

  • Agee, J.K. 1993. Fire Ecology of Pacific Northwest Forests. Island Press. 493 pp.
  • DeBano, L.F., D.G. Neary and P.F. Ffolliott. 1998. Fire's Effects on Ecosystems. John Wiley & Sons, NY. 333 pp.
  • McPherson, G.R., D.D. Wade and C.B. Phillips. 1990. Glossary of Wildland Fire Management Terms Used in the United States. Soc. of American Foresters, Washington, DC.
  • Romme, W. 1980. Fire history terminology: report of the ad hoc committee. pp. 135-137. M.A. Stokes and J.H. Dieterich (tech. coord.). Proceedings of the Fire History Workshop, Oct. 20-24, 1980, Tucson, AZ. USDA For. Service, RMFRES GTR-81. 142 pp.

Last updated: March 1, 2015

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