National Wildfire Coordinating Group

NWCG Glossary of Wildland Fire, PMS 205

This glossary provides the wildland fire community a single source for wildland fire and incident management terminology commonly used by the NWCG and its subgroups.

Glossary entries related to Organizations, IT Applications, and NWCG Positions have been removed from the glossary based on term inclusion criteria. For more information about the glossary and the criteria, see the About the NWCG Glossary page or the NWCG User Guide for the Glossary of Wildland Fire, PMS 937.

Reference Definitions

Some of the terms within this glossary will be followed by initials or will have references or comments at the end of the definition to help broaden the recognition and understanding of the term. An explanation of those references is as follows:

Also called: Means there is another term that may sometimes be in use, but is not defined in this glossary.
Acronym: An abbreviation formed from the initial letters of other words and pronounced as a word. An acronym appears in parentheses following the term.
Initialism: An abbreviation consisting of initial letters pronounced separately. An initialism appears in parentheses following the term.
See: Means there is another, preferred term that should be used instead. In such a case only the preferred term is defined in this glossary.
See Also: Means there are one or more related terms that may also be of interest to the glossary user. The related terms are also defined in this glossary.
Synonym: Means the term is synonymous with another. The terms have the same, or essentially the same, definition and the terms are interchangeable in their use.
Definition Extension: An example, further explanation, or usage guidance in support of the definition.

Glossary Acronyms/Initialisms

6 (1) | A (126) | B (94) | C (160) | D (102) | E (67) | F (261) | G (48) | H (90) | I (83) | J (10) | K (4) | L (74) | M (92) | N (31) | O (47) | P (133) | Q (6) | R (100) | S (221) | T (71) | U (28) | V (37) | W (60) | Z (1)
Gallons per Minute (GPM)
  • The measure of water flow in firefighting. It is used to measure the output of wildland and structural fire engines, pumps, hose streams, nozzles, hydrants, and water mains. 
  • Weak or missed area in a retardant drop or in a fireline. 
Gate Valve
  • A valve with a gate-like disk that moves up and down at right angles to the flow when actuated by a stem screw and hand wheel. Gate valves are best for service that requires infrequent valve operation and where the disk is kept either fully open or closed. 
Gear Pump
  • Positive displacement pump which uses closely meshed gears to propel water when high pressures and low volumes are desired; can be used safely only with clear water-- suspended particles of soil or rocks can quickly wear the gears and reduce pressure and volume of water. 
General Fire Weather Forecast
  • A forecast, issued daily during the regular fire season to resource management agencies, that is intended for planning of daily fire management activities, including daily staffing levels, prevention programs, and initial attack on wildfires. Also called presuppression forecast. 
General Origin Area (GOA)
  • The larger area where the fire first established itself and is identified by an analysis of the fire behavior context, macroscale fire pattern indicators, and witness statements. Source: Guide to Wildland Fire Origin and Cause Determination, PMS 412.
    • Definition Extension: The general origin area includes within its boundary the specific origin area and ignition area and is typically less than ½ acre in size.     
General Schedule Employee
  • A regular federal government employee who is compensated under the General Schedule (GS) Pay Plan.
General Staff
  • The group of incident management personnel reporting to the Incident Commander. They may each have a deputy, as needed. The General Staff consists of: Operations Section Chief, Planning Section Chief, Logistics Section Chief, and Finance/Administration Section Chief. 
General Winds
  • Large scale winds caused by high- and low-pressure systems but generally influenced and modified in the lower atmosphere by terrain. 
Geographic Area
  • A boundary designated by governmental agencies (wildland fire protection agencies) within which they work together for the interagency, intergovernmental planning, coordination, and operations leadership for the effective utilization of emergency management resources within their area. There are nine geographic areas. A listing of the areas can be found in the National Interagency Mobilization Guide, Chapter 70 along with listings of the Geographic Coordinating Areas and Geographic Area Coordination Centers. 
Geographic Area Coordinating Group (GACG)
  • An interagency body of fire management representatives from each federal and state land management agency within a nationally recognized regional area that provides leadership and support to facilitate safe and efficient fire management activities. Working collaboratively, a GACG's mission is not only for wildland fire emergencies, but for other emergency incidents, as necessary.
Geographic Area Coordination Center (GACC)
  • The physical location of an interagency, regional operation center for the effective coordination, mobilization and demobilization of emergency management resources. A coordination center serves federal, state and local wildland fire agencies through logistical coordination of resources throughout the geographic area, and with other geographic areas, as well. Listings of geographic coordination centers and their respective geographic coordinating areas can be found within the National Interagency Mobilization Guide. 
Geographic Coordinating Area
  • A boundary designated by governmental agencies (wildland fire protection agencies), that may coincide with a geographic area boundary or may be a subdivision of a geographic area within which they work together coordinating, for the effective, mobilization and demobilization of emergency management resources within their area. Listings of geographic coordinating areas and geographic coordination centers can be found in the National Interagency Mobilization Guide, Chapter 20, Section 21.1. 
Geostationary Operational Environmental Satellite (GOES)
Getaway Time
  • Elapsed time from receipt of notification by the personnel charged with initiating suppression action to the departure of the first attack unit. 
Global Positioning System (GPS)
  • A system of navigational satellites operated by the U.S. Department of Defense and available for civilian use. The system can track objects anywhere in the world with an accuracy of approximately 40 feet. 
Glowing Combustion
  • The process of oxidation of solid fuel accompanied by incandescence. All volatiles have already been driven off, oxygen reaches the combustion surfaces, and there is no visible smoke. This phase follows the smoldering combustion phase and continues until the temperature drops below the combustion threshold value, or until only non-combustible ash remains. 
Glowing Combustion Phase
  • The final phase of combustion following flaming and smoldering phases. 
Going Fire
  • Any wildfire on which suppression action has not reached an extensive mop up stage. 
Government Vehicle
  • A vehicle owned by, on loan to, leased or rented by the government.
Gradient Wind
  1. Wind flowing parallel to pressure isobars or contours with low pressure on the left of the observer in the Northern Hemisphere; velocity such that the pressure gradient, Coriolis, and centrifugal force acting in the area are in balance.
  2. Wind created by differing barometric pressures between high- and low-pressure systems. Velocity is generally five to 30 miles per hour, and wind shifts are usually gradual as systems move and shift. 
Grass Fire
  • Any fire in which the predominant fuel is grass or grasslike. 
Grass Type
  • In NFDRS, the two grass types (annual, perennial) determine how seasonal drying of live herbaceous fuels is modeled. 
  • Of, or pertaining to, measurement by weight. 
Gravity Tank
  • Water storage tank for fire protection and sometimes community water service that supplies water by gravity pressure. 
  • Green-up for the 1978 version of NFDRS model is defined as the beginning of a new cycle of plant growth. Green-up usually occurs once a year, except in desert areas where rainy periods can produce a flush of new growth more than once a year. Green-up may be signaled at different dates for different fuel models. Green-up should not be started when the first flush of green occurs in the area. Instead, the vegetation that will be the fire problem (represented by the NFDRS fuel model associated with the weather station) when it matures and cures should be identified. Green-up should start when the majority of this vegetation starts to grow. 
  • Landscaped and regularly maintained fuel break, usually put to some additional use (e.g., golf course, park, playground). 
Greenhouse Effect
  • The heating of the earth's surface by both atmospheric infrared radiation and incoming solar radiation. 
Greenness Factor
  • In the 1988 version of NFDRS, a code scaled from 0 to 20 representing the greenness of grasses and shrubs from near dead to maximum greenness. 
Grid Ignition Technique
  • Method of igniting prescribed fires in which ignition points are set individually at predetermined spacing with predetermined timing throughout the area to be burned. Also called point source ignition technique. 
Grid Search Technique
  • To search for a small fire by systematically traveling over an area on parallel courses or gridlines. 
Gross Axle Weight Rating (GAWR)
  • The value specified by the manufacturer as the maximum allowable weight placed on an axle of a vehicle when fully equipped, including payload, fluids and occupants. 
Gross Vehicle Weight (GVW)
  • Actual vehicle weight, including chassis, body, cab, equipment, water, fuel, crew, and all other load. 
Gross Vehicle Weight Rating (GVWR)
  • The value specified by the manufacturer as the maximum allowable weight of a vehicle fully equipped, including payload, fluids and occupants. 
Gross Weight
  • Total allowable weight of a loaded aircraft for takeoff or landing, adjusted for altitude differences. 
Ground Effect
  • Reaction of a rotor downdraft against the ground surface, forming a "ground cushion" that increases lifting capability of that section of air.
Ground Fire
  • Fire that consumes the organic material beneath the surface litter ground, such as a peat fire. 
Ground Fog
  • Fog which extends vertically to less than 20 feet. 
Ground Fuel
  • All combustible materials below the surface litter, including duff, tree or shrub roots, punky wood, peat, and sawdust, that normally support a glowing combustion without flame. 
Ground Speed
  • Speed with which an aircraft traverses the ground over which it flies. 
Ground Support Unit
  • Functional unit within the Logistics Section responsible for the fueling, maintaining and repairing of vehicles, and the transportation of personnel and supplies. 
Ground Truth
  • Verification at the site of what has been observed and/or measured from aircraft, satellites, other aerial platforms, aerial photographs, or maps. 
Ground Visibility
  • Horizontal visibility observed at the ground. 
  • Groups are established to divide the incident into functional areas of operation. Groups are composed of resources assembled to perform a special function not necessarily within a single geographic division. Groups, when activated, are located between branches and resources in the operations section. 
Growing Season Burning
  • Prescribed burning or use of wildland fire during the photosynthetically-active growing season, where live fuel moistures are relatively high and the dominant vegetation, grasses, forbs, and herbaceous vegetation are fully greened. 
Gum Thickened Sulphate (GTS)
  • A dry chemical product which is mixed with water to form a fire retardant slurry. 
  • Rapid fluctuations in wind speed with a variation of 10 knots (11.5 mph) or more between peaks and lulls.