Black-- Refers to areas where a fire has recently burned and consequently fuel no longer exists. The “black” may be used as an area of safety from wildfire in the event of an emergency.

Blackline --Refers to a strip adjacent to a control line that is intentionally burned in order to contain a fire. Many prescribed fire and wildfire suppression techniques are based on the concept of blackline as a barrier to fire spread.

Bucket drop-- Water dropped by a helicopter enabled with a sling and a remotely operated bucket that is filled from a water source.  

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

Control line-- A line in which fuels have been removed. A control line may be dug by a fire crew (a hand line) or by machinery such as a bulldozer (a dozer line). Sometimes a control line is established by wetting fuels using engines and fire hoses (a wet line). A control line may also consist of a road, river, snowbank, rock outcropping or other barrier to fire spread.

Cover type-- A standardized description of the vegetation in Yellowstone in which a fire is burning. The cover type is based on the dominant tree species and the age of the forest. Cover types help predict site moisture, fuel loading and fire behavior (see Vegetation).

Drip torch-- An ignition tool which drips a flaming mixture of diesel and gasoline onto the ground.

Dry lightning-- Lightning from a thunderstorm that gives little or no precipitation.

Fire, backing-- Fire that is moving into the wind (See heading and flanking fire). Backing fires burn with a slower rate of spread than heading fires.

Firebrands-- Burning material thrown in the air. Firebrands may be thrown ahead of a main fire, or rain down from a burning snag or tree.

Fire, creeping-- A low intensity fire with a low rate of spread.

Fire, crown-- A fire that burns through the canopy of a forest.

Fire cycle-- The time needed to burn a unit area of interest.

Fire extent-- The area burned per time period or event.

Fire, flanking-- Fire that is moving perpendicular or at an angle to the wind direction (See heading and backing fire).

Fire, ground-- Fire burning on the ground or through the understory and not reaching into the canopy. Also called surface fire.

Fire, heading-- Fire that is moving with the wind (See backing and flanking fire). Heading fires burn with a faster rate of spread than backing fires.

Fire intensity-- Energy release per unit length of flame front (kW/m or BTU/ft-s). Flame lengths of about 4' (1.2 m) correspond roughly to 100 BTU/ft-s (29 kW/m), and is the approximate limit of control by direct attack by a hand crew.

Fire Names-- The normal procedure or protocol is that a fire is named by the Incident Commander. The name is usually taken from some local geological feature.

Fire return interval-- The average amount of time between successive fires. Fire return interval may be specified for a single point on the landscape (point fire return interval) or for an area of a specified size.

Fire, stand replacement-- A fire of such intensity and severity that nearly all the trees in a stand are killed. Forests succeeding a stand replacing fire are generally composed of trees that quickly re-establish and are consequently evenly aged. 

Fire, torching-- Fire burning principally as a surface fire that intermittently burns into the crowns of individual trees.

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

Foam--  Water in which a surfactant has been added at the pump. Foam insulates fuels against heat, increases the penetration of water into fuels and decreases evaporation.

Fuel-- Combustible material available to a fire. Fuels are classified according to the amount of time a fuel gains or loses moisture: 1 Hour, generally drying out within 1 hour (<1/4" or 64 mm in diameter), 10 Hour, drying out within 10 hours (1/4"-1" or 64-254 mm), 100 Hour, drying out within 4 days (1-3" or 2.5-7.6 cm), 1000 Hour, generally drying out within 42 days (>3" or <7.6 cm). Fuels may also be referred to as fine, (needles, leaves, lichen etc.), live or green, (living foliage, branches etc.), downed, (fuel on the ground), or heavy, (large logs and snags).

Fuel, Carrier-- Fuels that allow a fire to spread and "carry" through the forest. These are generally lighter fuels such as conifer needles, leaves, cured grass and small twigs.  

Fuel load-- The mass of available fuel per unit area (kg/m² or tons/acre).

Fuel model-- A standardized description of fuel potentially available to a fire. Fuel load is based on the dominant vegetation and the amount, distribution and continuity of wood and other combustible material (see Vegetation).

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. In a normal fire season 1000 hour fuels may average about 18% fuel moisture. During extreme drought years, 1000 hour fuel moistures may reach as low as 7%. 

Hazard Fuels-- Fuels posing a threat to people or property in the event of a wildfire.

Inversion, (or temperature inversion)-- Under high pressure and stable air conditions warm air may cap cooler air, forming an inversion that traps smoke in valley bottoms, particularly at night.

Jackpot-- A pocket of heavy fuels (e.g., downed logs) that may flare up in an area where the fuel load is otherwise low.

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

Lookout--  A member of a fire crew whose job is to monitor local weather conditions, and to identify and report potential dangers resulting from a change in fire behavior or weather. A lookout may also refer to one of the towers on Mount Washburn, Sheridan or Holmes in Yellowstone, or to the employees stationed there whose job is to detect fire starts.

Lost ignition-- A natural ignition that was suppressed. Some agencies may re-ignite a lost ignition at a more convenient, later date to salvage a natural process.

Names, Fire-- The normal procedure or protocol is that a fire is named by the Incident Commander. The name is usually taken from some local geological feature.

Preheating-- An increase in the flammability of fuels due to exposure to heat and convective wind ahead of a fire.

Prescribed Fire-- Generally a management ignited fire that is allowed to burn within a prescription of weather and safety considerations. May also refer to a natural ignition that is allowed to burn as long as it stays within prescription. Currently in Yellowstone National Park plans for prescribed burning are limited in use to hazardous fuel reductions around Park infrastructure. Other agencies may use prescribed burning to increase forage production, maintain fire dependent ecosystems, or reduce slash after timber harvest.

Prescription-- Measurable criteria which define conditions under which a prescribed fire may be ignited or allowed to burn. Prescription criteria include safety, weather, environmental, geographic, administrative, social or legal considerations.

Relative humidity-- The ratio of absolute to saturation vapor pressure. The ratio of how much vapor the air actually holds relative to how much it could potentially hold at a given temperature and pressure. For example, a parcel of air may hold only 20% of the vapor that it is capable of holding. Fire behavior is dependent on, and can be predicted from relative humidity. 

Rate of spread-- The speed a flame front travels (m/hr, chains/hr, ft/hr).

Snag-- A standing dead tree. Snags are a hazard to fire fighters because the roots burn out causing the tree to unexpectedly fall, particularly if conditions are windy. Burning snags may also throw sparks and fire brands ahead of a fire front, causing spot fires.

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

Wildfire-- An unwanted wildland fire.

Wildland Fire-- Any non-structure fire that occurs in the wildland. This term encompasses wildfires and prescribed natural fires.

Wildland Fire for Resource Benefit (WFRB or “Wooferb”) or Wildland Fire Use Fire-- Naturally ignited fires that are allowed to burn within prescription in order to maintain natural ecosystem processes.  

See also the Fire Effects Information System fire terms glossary:

http://www.fs.fed.us/database/feis/glossary.html