National Weather Service United States Department of Commerce


Fire Weather Terms and Definitions


Air Attack  - The deployment of aircraft on a wildland fire to drop retardant, shuttle crew and supplies, or perform reconnaissance.

Air Drop  - Dropping fire retardant from an aircraft onto a wildland fire.

Air Tanker  - A fixed wing aircraft used to drop fire retardant on a fire.

Aspect  - The direction towards which a slope faces.

Backfire  - A fire suppression technique of creating a fire break by burning all fuel between the existing fire line and the oncoming fire. It can also be used to change the direction and force of the fire convection column.

Backpack/Bladder pump  - A water bag with a short length of hose and a pump type nozel carried as a backpack by firefighters.

Blowup  - Sudden increase in intensity or rate of spread of fire. Often accompanied by violent convection that resembles or may have characteristics of a fire storm. This can occur when atmospheric temperature and wind increases and humidity decreases.

Break over/Slop over  - A fire edge that crosses a line intended to control the fire.

Burning conditions  - The environmental factors that affect fire.

Burning index  - A number that describes anticipated fire behavior and how difficult it will be to control the fire.

Burn out  - This is a process of igniting a fire between the control line and the wildland fire. It's purpose is to burn any fuel remaining in a controlled way so that the wildland fire will have nothing further to consume and will die out.

Canopy  - The foliage and branches making up the "roof" of the forest.

Cat line  - A fire line constructed by a bulldozer or caterpillar.

Cold Trailing  - Usually a part of the "Mop-up" process of making sure a fire is completely out. Firefighters actually feel the fire area with their gloved hands to find any remaining hot spots and then put them out.

Command Post (ICP)  - For very large fires, a command post is set up to manage all fire operations.

Contain a fire  - An effort to prevent further spread of the fire.

Control a fire  - A fire is considered "controlled" when it is completely surrounded by a "control line," which is expected to hold any further fire spread.

Control line  - Also often called a "fire line," this includes line constructed by firefighters as well as natural barriers to fire such as rock outcroppings, roads, and streams or other waterbodies. Crews construct fire lines by using shovels, pulaskis, rakes and chainsaws to clear the line of vegetation so that the fire will have nothing to burn when it arrives at that point.

Crew Boss  - The supervisor for 5 to 20 firefighters.

Crown fire  - A fire that runs from top to top of trees or shrubs. This kind of fire can be extremely difficult to stop.

Crown Out  - Where a fire has a "ladder" of fuels to climb (grass to shrubs to small trees to large trees), it may rise from ground level to canopy level and begin advancing from tree top to tree top.

Drift smoke  - Smoke that has drifted from its point of origin and has lost its original "billow" form. Drift smoke sometimes gives the false impression of a fire in the general area to which it has drifted.

Drip torch  - A small fuel tank with a handle, nozzle and igniter used to drip a burning mixture of oil and gasoline to ignite a prescribed fire or a backfire.

Drought index  - A number representing the moisture level in duff or upper soil layers. It measures the evaporation, transpiration and precipitation that has occured.

Dry Lightning - A lightning storm with only trace precipitation.

Duff  - The partly decomposed organic material of the forest floor beneath the litter of freshly fallen twigs, needles and leaves.

Extreme fire behavior  - Winds, steep slopes, and highly combustible vegetation can combine to produce a fire with the potential to spread rapidly and unpredictably. These fires are potentially very dangerous.

Entrapment  - A situation in where personnel are unexpectedly caught in fire behavior-related, life threatening position where planned escape routes or safety zones are absent, inadequate, or compromised. An entrapment may or may not include deployment of a fire shelter for its intended purpose. These situations may or may not result in injury. They include near misses.

Fine Fuel Moisture  - The moisture content of fast drying fuels such as grass, leaves, ferns, tree moss, draped pine needles and small twigs.

Fire Retardant  - A substance that uses chemical or physical action to reduce flammability of fuels and slow the rate of their combustion.

Fire shelter  - Looking very much like an aluminum foil puptent, the fireshelter is carried by each firefighter. If trapped by a fire, a crew boss will instruct his members to "deploy" the shelters. Firefighters find an area clear of burnable vegetation, or clear an area themselves. Then they place their hands and feet in straps at each corner of the shelter and lay on the ground on their stomachs with their feet towards the advancing fire. The tent traps air over them which is maintained at a cooler temperature than the surrounding fire by the reflective material contained in the shelter's fabric. This trapped cool air protects the firefighters' lungs from the hot air of the fire and the shelter shields them from the flames themselves. Firefighters remain in the shelters until released by the crew boss. This may take some time as they must be completely confident that they are no longer in danger from the fire.

Fire weather  - A weather prediction prepared specifically for use by fire managers. It covers weather elements that may have direct impacts on fire behavior and how a fire is attacked.

Fire break  - A natural or constructed barrier used to stop or check fires.

Fire line  - Also often called a "control line," this includes line constructed by firefighters as well as natural barriers to fire such as rock outcroppings, roads, and streams or other waterbodies. Crews construct fire lines by using shovels, pulaskis, rakes and chainsaws to clear the line of vegetation so that the fire will have nothing to burn when it arrives at that point.

Flame height  - The average maximum vertical extension of flames at the leading edge of the fire front. Occasional flashes that rise above the flames are not considered. This distance is less than the flame length if flames are tilted due to wind or slope.

Flaming Front  - That zone of a flaming fire where the combustion is primarily flaming. Behind this flaming zone, combustion is primarily glowing or burning out of larger fuels (greater than about 3 inches in diameter).

Flanking  - Attacking a fire by working along its edges. Flanking fire lines move towards the fire front where they are linked to stop the fire.

Flash/Fine Fuels  - Grass, leaves, pine needles, and other fuels which ignite easily and burn rapidly when dry.

FMO  - The Fire Management Office (FMO) has primary responsibility for directing how fires are managed in his area.

Foam  - A chemical fire extinguishing mixture. It adheres to fuels, cooling and moistening them. It also excludes oxygen from them, eliminating one of the items fire needs to burn.

Fuel Moisture content  - The quantity of moisture in fuel expressed as a percentage of the weight when thoroughly dried at 212 degrees Farenheit.

Fuel break  - A wide strip or block of land on which the native vegetation has been permanently modified so that fires burning into it can be more readily extinguished. In areas where Cheet grass is widespread, landowners or managers may install fuel breaks of some other less fire-prone vegetation to reduce the ability of cheet grass fires to spread.

Ground fire  - A fire that consumes the organic material on or beneath the surface litter of the forest floor.

Hand Crew  - A group of from 8 to 25 firefighters organized and trained to clear brush, cut trees and make fire lines with hand tools.

Head of fire  - The most rapidly spreading portion of a fire's perimieter.

Heavy fuels  - Fuels of large diameter such as snags, logs, and large limbwood, which ignite and are consumed more slowly than flash fuels. Also called coarse fuels.

Helibase  - The area where helicopters are parked, fueled, maintained and loaded.

Helispot  - A temporary landing spot for helicopters. Often these must be constructed by firefighters who remove all tall vegetation that might prevent the helicopter from landing.

HelitackCrew  - The firefighters who work from the helicopter. Though they assist in actual firefighting, their primary responsibilities include making sure firefighters and equipment are safely loaded and providing signals the pilot needs to take off and land.

Holdover fire  - A fire that remains dormant for a day or two before flaring up. Dry lightning storms often cause holdover fires.

Hotshot crew  - An intensively trained firefighting crew. Unlike hand crews whose membership changes often, hotshot crews remain together for an entire season and often for years at a time. They are based in specific areas or forests, but are often transported to fires across the country.

IC  - Incident Commander. When a team is called in to assist with fire suppression on a large fire, they are headed by an IC.

ICP  - Incident Command Post. The site from which the team works.

ICS  - Incident Command System. This system was designed to assist firefighters in doing their job. It provides direction for increasing the size and types of teams fighting fires to respond to the size and type of fire being suppressed.

Indirect attack  - A method of suppressing fires by building lines along natural firebreaks and using topography while staying some distance from the head of the fire.

Initial attack  - The first effort to contain a fire. If initial attack is not successful in stopping the fire and it continues to grow, larger teams are called in to assist.

Jump spot  - A landing spot selected for smokejumpers.

Ladder Fuels  - Fuels which provide vertical continuity between strata, thereby allowing fire to carry from surface fuels into the crowns of trees or shrubs with relative ease. They help initiate and assure the continuation of crowning.

Lead plane  - An aircraft directing air tankers to the fire. Lead planes can assist air tanker pilots in judging air currents in the area and in dropping the retardant at the correct spot on the fire.

Light unit  - A fire truck equipped with a generator, flood lights, and electrical tools for use in light fire fighting and rescue work.

Lightning Activity Level, LAL  - A number on a scale of 1 to 6 that described the relative frequency and character of cloud-to-ground lightning in an area. The 6 rating is a special level assigned when little or no rain is expected to reach the ground from thunderstorms. "Red Flag" warnings may be issued in association with a 6 rating.

Line Holding  - Ensuring that the established fireline has completely stopped fire progress.

Live fuel moisture  - A description by percent of the moisture in brush and trees.

Lookout  - (1) A person designated to detect and report fires from a ventage point. (2) A location from which fires can be detected and reported. (3) A fire crew member assigned to observe the fire and warn the crew when there is danger of becoming trapped.

Lookout(s), Communication(s), Escape route (s), and Safety Zone(s)  - Elements of a safety system used by fire fighters to routinely assess their current situation with respect to wildland firefighting hazards.

McLeod  - A scraping tool for line construction used in areas where duff is common.

Mop-up  - Once a fire is controlled, Mop-up begins. This is the process of making sure all remaining hot spots within the fire's perimeter are completely out. See cold-trailing.

Nomex  - Trade name for the heat resistant fiber used in firefighters' protective clothing.

Overhead  - Personnel assigned to supervisory positions, including incident commander, command staff, general staff, branch directors, supervisors, unit leaders, managers and staff.

Personal Protective Equipment (PPE)  - The equipment and clothing required to mitigate the risk of injury from or exposure to hazardous conditions encountered during the performance of duty. PPE includes, but is not limited to: fire resistant clothing, hard hat, flight helments, shroud, goggles, gloves, respirators, hearing protection, chainsaw chaps, and shelter.

Prescribed burning  - Prescribed fires allow us to incorporate fire in the ecosystem under controlled circumstances. Fire managers ignite them when weather conditions enhance our ability to confine them to predetermined areas and after crews have developed fire breaks or lines. These fires typically burn in a mosaic pattern, leaving unburned areas within their boundaries. Prescribed fires are used to improve forage and habitat for wildlife and livestock, to improve watershed, or to reduce hazardous build up of fire fuels.

Project fire  - A fire requiring more people and equipment than are available on the BLM District or Forest Ranger District where it is burning.

Pulaski  - A fireline building tool with a blade that is a combination of an axe and a hoe.

Reburn  - A fire may sometimes pass through an area without burning all materials there. These remaining materials, dried by the first fire pass, can reignite and the area may "reburn."

Red Card  - Fire qualification card issued to fire rated persons showing their qualifications and their training needs to fill specified fire suppression positions in a large fire suppression or incident organization.

Red flag warning - Issued when weather conditions could lead to extensive wildland fires.

Resource Order  - The form used by dispatchers, service personnel, and logistics coordinators to document the request, ordering or release of resources, and the tracking of those resources on an incident.

Retardant  - A substance dropped on fires from air tankers to reduce flammability of fuels.

Slash - Debris left after logging, pruning, thinning or brush cutting. It includes logs, limbs and understory trees or brush.

Slurry - Another name for retardant.

Smokejumper  - Specially trained firefighter who parachutes to fire sites.

Snag  - A standing dead tree or part of a dead tree from which at least the leaves and smaller branches have fallen.
Spot Fire - Fire ignited outside the perimeter of the main fire by a firebrand.

Trenching  - Digging trenches on a side slope to catch any burning or other materials which might roll across control lines.

Wildland-Urban Interface  - The line, area, or zone where structures and other human development meet or intermingle with undeveloped wildland or vegetative fuels.