Glossary

Aerial Fuels - Standing and supported live and dead forest combustibles not in direct contact with the ground consisting mainly of foliage, twigs, branches, cones, bark, stems, and vines (See Draped Fuels, Ladder Fuels)

Aspect - Direction toward which a slope faces.

Available Fuel - That portion of the total fuel that would actually be consumed under a specific set of burning conditions.

Backing Fire - A fire spreading or set to spread into (against) the wind, or downhill. (See: Flanking Fire, Heading Fire).

Belt Weather Kit - Belt mounted canvas case with fitted pockets for anemometer, compass, sling psychrometer, slide rule, water bottle, pencils, and book of weather report forms.

Blackline - Preburning of fuels, either adjacent to a control line before igniting the main prescribed fire, or along a roadway as a deterrent to human-caused fires. Blackline denotes a condition in which there is no unburned fine fuel.

Broadcast Burn - Prescribed fire that burns over a designated area, generally in the absence of a merchantable overstory, to consume debris that has not been piled or windrowed.

Burning Boss - Person responsible for managing a prescribed fire from ignition through mop-up.

Burning Index (BI) - A relative number related to the contribution fire behavior makes to the amount of effort needed to contain a fire within a given fuel type. A doubling of the BI indicates twice the effort will be needed to contain a fire in that fuel type as was previously required.

Catface - Defect on the surface of a tree resulting from a wound where healing has not re-established the normal cross-section.

Chain - Unit of measure in land survey equal to 66 feet; 80 chains equal 1 mile.

Clearcutting - Removal of the entire standing, merchantable timber crop.

Cold Front - The leading edge of a mass of air that is colder and drier than the air mass being replaced.

Control Line - Comprehensive term for all constructed or natural fire barriers and treated fire edges used to control a fire.

Convection Column - The rising column of gases, smoke and debris produced by a fire. The column has a strong vertical component indicating that buoyant forces override the ambient surface wind (See Smoke Plume).

Convergence Zone - The area of increased flame heights and fire intensity produced when two or more flame fronts burn together.

Crown Scorch - Browning of needles or leaves in the crown of a tree or shrub caused by heat from a fire.

Cured - Debris or herbaceous vegetation that has dried and lost its green color.

Draped Fuels - Needles, leaves, twigs, etc., that have fallen from above and have lodged on lower branches and brush. Part of aerial fuels.

Drift Smoke - Smoke that has been transported from its point of origin and in which convective motion no longer dominates.

Drip Torch - Hand-held apparatus used to ignite fires by dripping flaming liquid fuel, at an adjustable rate, on the materials to be burned. The fuel is generally a mixture of 65 to 80 percent diesel and 20 to 35 percent gasoline.

Drought Index (Keetch-Byram Drought Index) - A numerical rating of the net effect of evapotranspiration and precipitation in producing cumulative moisture depletion in deep duff or upper soil layers.

Dry-bulb Temperature - The temperature of the air.

Duff - The layer of decomposing organic materials lying below the litter layer and immediately above the mineral soil. It is comprised of the Fermentation (F) and Humus (H) layers of the forest floor.

Fine Fuels (Flash fuels) - Fast-drying, dead fuels which have a Timelag constant of 1 hour or less. These fuels ignite readily and are consumed rapidly when dry. Included are grass, leaves, draped pine needles, and small twigs.

Fire Behavior - A general term that refers to the combined effect of fuel, weather and topography on a fire.

Firebrand - Any flaming or smoldering material such as leaves, pine cones, or glowing charcoal that could start another fire.

Firebreak - Any natural or constructed discontinuity in a fuelbed used to segregate, stop, or control the spread of fire or to provide a control line from which to suppress a fire.

Fire Effects - Physical, biological and ecological impacts of fire on the environment.

Fire Front - The strip within which continuous flaming occurs along the fire perimeter (See Flame Depth).

Fireline Intensity (Byram's Intensity) - The rate of heat release per unit time per unit length of fire front. Numerically, it is the product of the heat yield, the quantity of fuel consumed in the Fire Front, and the rate of spread.

Fire Plow - Heavy-duty share or disk plow designed to be pulled by a tractor to construct Firebreaks.

Firing Technique - The type(s) of fire resulting from one or more ignition(s), e.g., backing fire, flanking fire, heading fire, (See Grid Ignition, Ignition Pattern).

Flame Depth - The depth of the Fire Front at the fuel surface.

Flame Length - The distance between the flame tip and the midpoint of the Flame Depth at the base of the flame (generally at the ground surface).

Flanking Fire - A Fire Front spreading, or set to spread at roughly right angles to the prevailing wind.

Fuel Moisture Content - Water content of a fuel expressed as a percentage of the ovendry weight of the fuel.

Fuel Moisture Indicator Sticks - A specially manufactured set of sticks of known dry weight continuously exposed to the weather and periodically weighed to determine changes in moisture content. The changes are an indication of changes in the moisture status and relative flammability of dead fuels that roughly correspond to Ten-hour Time lag Fuels.

Hazard Reduction - Treatment of living and dead forest fuels to reduce the likelihood of a fire starting, and to lessen its damage potential and resistance to control.

Heading Fire - A Fire Front spreading or set to spread with the wind or upslope.

Helitorch (Flying Drip Torch) - A specialized drip torch hung from, or mounted on a helicopter that dispenses globs of ignited gelled gasoline.

Herbaceous Fuels - Grasses and other plants that contain little woody tissue.

Humus -The layer of decomposed organic matter on the forest floor beneath the partially decomposed litter layer (F layer) and directly above the soil.

Ignition Pattern - The manner in which a Prescribed Fire is ignited. The distance between ignition lines or points and the sequence of igniting them, as determined by fuel, topography, weather, ignition system, firing technique, and other factors influencing fire behavior and the objectives of the burn.

In-stand Wind (Midflame Wind) – Wind speed within a stand at about eye level.

Inversion - defined as a layer of the atmosphere through which the temperature increases with increasing height.

Keetch-Byram Drought Index – (See Drought Index)

Ladder Fuels - Fuels that provide vertical continuity between the ground and tree crowns, thus creating a pathway for a surface fire to move into the overstory tree crowns.

Line Ignition - Setting a line of fire as opposed to individual spots.

Litter - The top layer (L layer) of the forest floor directly above the fermentation layer (F layer), composed mainly of recently fallen leaves and pine needles, but also includes dead twigs, bark fragments, etc. (See Duff).

Logging Debris - Unwanted tree parts remaining after harvest, including tree crowns, unutilized logs, and uprooted stumps.

Midflame Wind - See In-stand wind. Mineral Soil-Soil layers below the predominantly organic horizons.

Mixing Height - The height to which relatively vigorous mixing of the atmosphere occurs.

Mopup - Extinguishing or removing burning material, especially near control lines after an area has burned to make it safe, or to reduce residual smoke.

Muck – (See Organic Soil).

National Fire Danger Rating System (NFDRS) - The method currently used by the USDA Forest Service, and many other organizations to integrate the effects of topography, fuels, and weather into numerical indices of fire danger on a day-to-day basis.

One-Hour Fuels - Fine fuels consisting mainly of dead herbaceous plants, roundwood less than about 1/4-inch in diameter, and the uppermost Litter Layer.

Organic Soil - Any soil or soil horizon containing at least 30 percent organic matter; examples are peat and muck.

Peat – (See Organic Soil).

Ping-pong Ball System - A method of igniting fires with the use of a Delayed Aerial Ignition Device (DAID) The device is a polystyrene ball, 1.25 inches in diameter that contains a combustible chemical The balls are fed into a dispenser, generally mounted in a helicopter, where they are injected with another chemical and drop through a chute leading out of the helicopter. The chemicals react thermally and ignite in about 30 seconds. The space between ignition points on the ground is primarily a function of helicopter speed, gear ratio of the dispenser, and the number of chutes used.

Prescribed Burning - The controlled application of fire to wildland fuels in either a natural or modified state, under specified environmental conditions which allow the fire to be confined to a predetermined area and at the same time produce the intensity required to attain planned resource management objectives.

Psychrometer - The general name for instruments designed to determine the moisture content of air. A psychrometer consists of dry-and wet-bulb thermometers that give the Dry-and Wet-bulb Temperatures, which in turn are used to determine Relative Humidity and Dew Point.

Relative Humidity - The ratio, expressed as a percentage of the amount of moisture in the air, to the maximum amount of moisture the air is capable of holding under the same conditions.

Residual Smoke - Smoke produced by smoldering material behind the actively burning Fire Front.

Ring Fire - A fire started by igniting the perimeter of the intended burn area so that the ensuing Fire Fronts converge toward the center of the block.

Rough - The live understory and dead fuels that build up on the forest floor over time.

Scorch Height (Scorch Line) - The average height to which foliage has been browned by fire.

Site Prep Burn - A fire set to expose adequate mineral soil and control competing vegetation until seedlings of the desired species become established

Slash - Debris resulting from such natural events as wind, fire, or snow breakage, or such human activities as logging or road construction.

Smoke Management - Application of knowledge of fire behavior and meteorological processes to minimize air quality degradation during Prescribed Burning.

Smoke Plume - The gases, smoke, and debris that rise slowly from a fire while being carried along the ground because the buoyant forces are exceeded by those of the ambient surface wind (See Convection Column).

Spot Fire - Fire ignited outside the perimeter of the main fire by a Fire Brand.

Spot Weather Forecast - Special prediction of atmospheric conditions at a specific site, sometimes requested by the Burning Boss before igniting a prescribed fire.

Strip-Heading Fire - A series of lines of fire upwind (or downslope) of a firebreak or backing fire that will burn with the wind toward the firebreak or backing fire.

Ten-Hour Fuels - Dead roundwood ¼ to 1 inch in diameter and, to a rough approximation, the top 3/4 inch of the litter layer.

Tractor - Plow-Any tracked vehicle, with a plow for exposing mineral soil, with transportation and personnel for its operation.

Transport Windspeed - A measure of the average rate of the horizontal movement of air throughout the mixing layer.

Underburning - Prescribed burning under a timber canopy.

Ventilation Factor - An indicator of the lower atmosphere's potential to diffuse and disperse smoke. Numerically, it is the product of the Mixing Height and the Transport Windspeed.

Wet-bulb Temperature - Technically, the temperature registered by the wet-bulb thermometer of a Psychrometer. It is the lowest temperature to which air can be cooled by evaporating water into it at a constant atmospheric pressure.

Wetline - A line of water, or water and chemical retardant, sprayed along the ground and which serves as a temporary control line from which to ignite or stop a low-intensity fire.

Wind Direction - Compass direction from which the wind is blowing.

Wind Profile - A plot of windspeed over height above the earth's surface. A rapid increase with height to a maximum windspeed within 1,000 feet above ground and then a slow decrease above that peak is commonly called a low-level jet and is one of several adverse wind profiles.

Windrow - Woody debris that has been piled into a long continuous row.

Source: US Department of the Interior, National Park Service