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)
Haines Index
  • An atmospheric index used to indicate the potential for wildfire growth by measuring the stability and dryness of the air over a fire. 
Hand Crew
  • A number of individuals that have been organized and trained and are supervised principally for operational assignments on an incident. 
  • Fireline constructed with hand tools. 
Hangup (Tree Falling)
  • A situation in which a tree is lodged in another, preventing it from falling to the ground. 
Hard Suction Hose
  • Noncollapsible suction hose attached to a pump and used to draft water from a source lower than the pump. Customary hose sizes in wildland fire engines are 2 and 2-1/2 inches in diameter (51 and 64 mm). 
  • Any real or potential condition that can cause injury, illness or death of personnel, or damage to, or loss of equipment or property. 
Hazard Assessment
  • Assess hazards to determine risks. Assess the impact of each hazard in terms of potential loss, cost, or strategic degradation based on probability and severity. 
Hazard Fuel
  • A fuel complex defined by kind, arrangement, volume, condition, and location that presents a threat of ignition and resistance to control. 
Hazard Map
  • Map of the area of operations that shows all of the known aerial hazards, including but not limited to power lines, military training areas, hang gliding areas, etc. 
Hazard Pay
  • A salary differential that compensates employees for exposure to hazards in the course of their duties. 
Hazard Reduction
  • Any treatment of living and dead fuels that reduces the potential spread or consequences of fire. 
Hazardous Areas
  • Those wildland areas where the combination of vegetation, topography, weather, and the threat of fire to life and property create difficult and dangerous problems. 
Hazardous Materials
  1. Substances that are identified, classified, and regulated in the Code of Federal Regulations, Title 49 and Hazardous Materials Regulations 175.
  2. A substance or material which has been determined by the Secretary of Transportation to be capable of posing an unreasonable risk to health, safety, and property when transported in commerce and which has been so designated. 
  • A sufficient concentration of atmospheric aerosols to affect a visible attenuation of light and measurable reduction in visual range. The aerosol particle diameter is near the wavelength of visible light, optimizing the light scattering efficiency of the particles. 
Haze Meter
  • Instrument for measuring the dependable range of distance at which a standard smoke column can be detected by the unaided eye under existing haze conditions. 
Head Fire
  • A fire spreading or set to spread with the wind. 
Head of the Fire
Head Pressure
  • Pressure due to elevation of water. Equals 0.433 pounds per square inch (PSI) per foot of elevation. (Approximately 0.5 PSI is required to lift water 1 foot in elevation) 
  • The compass direction in which the longitudinal axis of the aircraft points. 
  • Flashlight, ordinarily worn by firefighter on the front of the helmet. 
  • Temperatures higher than that of the normal atmosphere, produced by the process of burning or oxidation. 
Heat Content
  • The net amount of heat that would be given off if fuel burns when it is absolutely dry, noted as Btu per pound of fuel. 
Heat Low
  • An area of low pressure caused by intense heating of the earth's surface. High surface temperature causes air to expand and rise, resulting in low atmospheric pressure and induces a weak inflow of air at the surface. Air which rises in a heat low is very dry so clouds seldom form. Rising air above a heat low produces a warm upper level high and results in a net outflow of air aloft. Heat lows remain practically stationary over areas which produce them. 
Heat of Combustion
  • The heat energy resulting from the complete combustion of a fuel, expressed as the quantity of heat per unit weight of fuel. The high heat of combustion is the potential available, and the low heat of combustion is the high heat of combustion minus several losses that occur in an open system (primarily heat of vaporization of moisture in the fuel) . 
Heat per Unit Area
  • Total amount of heat released per unit area as the flaming front of the fire passes, expressed as Btu/square foot; a measure of the total amount of heat released in flames. 
Heat Probe
  • Apparatus used to detect heat. 
Heat Release Rate
  1. Total amount of heat produced per unit mass of fuel consumed per unit time.
  2. Amount of heat released to the atmosphere from the convective-lift fire phase of a fire per unit time. 
Heat Transfer
  • Process by which heat is imparted from one body to another, through conduction, convection, and radiation. 
Heat Trough
  • A Heat Low which is elongated in shape. Also called: Heat Low; Thermal Low; Thermal Trough. 
Heat Value
  • The total heat energy released during combustion, usually published as units of heat energy produced per unit mass of ovendry fuel consumed. 
Heat Yield
  • The heat of combustion corrected for various heat losses, mainly the presence of moisture in the fuel. To a very close approximation, the quantity of heat per pound of fuel burned that passes through a cross section of the convection column above a fire that is burning in a neutrally stable atmosphere. Also called low heat of combustion. 
Heavy Equipment Transport
  • Any ground vehicle capable of transporting a dozer, tractor, or other heavy piece of equipment. Also called lowboy. 
Heavy Fuels
  • Fuels of large diameter such as snags, logs, large limbwood, which ignite and are consumed more slowly than flash fuels. Also called coarse fuels. 
Heel of the Fire
  • The vertical measurement of vegetation from the top of the crown to ground level. 
Held Line
  • All control line that still contains the fire when mopup is completed. Excludes lost line, natural barriers not backfired, and unused secondary lines. 
  • The main location within the general incident area for parking, fueling, maintenance, and loading of helicopters. It is usually located at or near the incident base. 
Helibase Crew
  • A crew of individuals who may be assigned to support helicopter operations. 
  • Specially designed bucket carried by a helicopter like a sling load and used for aerial delivery of water or fire retardants. 
Helicopter Tender
  • A ground service vehicle capable of supplying fuel and support equipment to helicopters. 
  • A permanent facility for the operation of helicopters which has been built to FAA standards and which is marked on aeronautical charts. Natural resource agencies refer to agency heliports as permanent helibases. 
  • Lightweight portable pump developed for transport by helicopter. 
  • A natural or improved takeoff and landing area intended for temporary or occasional helicopter use. 
  • The utilization of helicopters to transport crews, equipment, and fire retardants or suppressants to the fireline during the initial stages of a fire. The term also refers to the crew that performs helicopter management and attack activities. 
Helitack Crew
  • A crew of firefighters specially trained and certified in the tactical and logistical use of helicopters for fire suppression. 
  • Specially designed tank, generally of fabric or metal, fitted closely to the bottom of a helicopter and used for transporting and dropping suppressants or fire retardants. 
  • A helicopter equipped with a fixed tank, Airtanker Board certified, capable of delivering a minimum of 1,100 gallons of water, foam, or retardant. 
  • A plant that does not develop woody, persistent tissue but is relatively soft or succulent and sprouts from the base (perennials) or develops from seed (annuals) each year. Includes grasses, forbs and ferns. 
Herbaceous Fuel Moisture
  • In NFDRS, a calculated value representing the approximate moisture content of the live herbaceous vegetation in the rating area expressed as a percentage of the oven dry weight of the sample. 
Herbaceous Stage
  • The modeled condition of herbaceous vegetation (pre-green, green-up, transition, cured, frozen) for the 1978 version of NFDRS. 
Hidden Fire Scar
  • Fire scar in a tree resulting from fire injury to the cambium without destruction of the overlying bark and therefore not readily discernible. 
Higbee Cut
  • Removal of the first (i.e., outside) thread of a female or male coupling to prevent crossing or mutilation of threads. Dimpled rocker lug on female coupling indicates beginning of Higbee Cut. 
High Expansion
  • Foam with an expansion between 201:1 and 1000:1. 
High Fire Risk Day
High Pressure Fog
  • Small capacity spray jet produced at very high pressures (greater than 250 psi, the normal maximum pressure for standard ground tankers) and discharged through a small hose with a gun-type nozzle. 
Historical Weather Station
  • In WIMS, a weather station that is no longer in service for which access to archived observations is still available in NIFMID. 
Holding Actions
  • All actions taken to stop the spread of fire. 
Holding Orbit
  • A predetermined maneuver which keeps an aircraft within a specified airspace while awaiting further orders. 
Holding Resources
  • Resources assigned to do all required fire suppression work following fireline construction but generally not including extensive mopup.  Also known as Holding Forces.
Holdover Fire
  • A fire that remains dormant for a considerable time. Also called sleeper fire. 
  • An adjective that describes a permanent place associated with a resource.
Home Assessment
  • Evaluation of a dwelling and its immediate surrounding to determine its potential to escape damage by an approaching wildland fire. Includes the fuels and vegetation in the yard and adjacent to the structure, roof environment, decking and siding materials, prevailing winds, topography, fire history, etc., with the intent of mitigating fire hazards and risks. 
Home Ignition Zone (HIZ)
  • The area where the factors that principally determine home ignition potential during extreme wildfire behavior (high fire intensities and burning embers) are present. The characteristics of a home and its immediate surroundings within 100 feet comprise the HIZ.
Home Location
  • The physical location of a resource when not on assignment.
Home Unit
  • The designated agency or entity providing contracted resources that employs the individual who is actively pursuing a position performance assignment (completion of a position task book). 
Horizontal Fuels Arrangement
  • Composition of fuel laterally across the landscape.
Hose Clamp
  • Crimping device for stopping the flow of water in a hose. 
Hose Lay
  • Arrangement of connected lengths of fire hose and accessories on the ground, beginning at the first pumping unit and ending at the point of water delivery. 
Hose Line Tee
  • A fitting that may be installed between lengths of hose to provide an independently controlled outlet for a branch line. 
Hose Rack
  • Item for storing drying fire hose. 
Hose Reel
  • A rotating drum used for winding booster hose (normally) for storing and dispensing. 
Hose Thread
  • The specific dimensions of screw thread employed to coupled fire hose and equipment. American National Standards (NH) have been adopted for fire hose couplings threads in 3/4, 1-1/2, 2-1/2, 3-1/2, 4, 5, and 6-inch sizes. 
Hose Washer
  • Device for cleaning the exterior of fire hose. 
  • A term historically used to indicate the agency or unit with jurisdiction or protection responsibilities or who was financially responsible for the incident response. Its use is not recommended.
Hotshot Crew
  • Intensively trained fire crew used primarily in handline construction (Type-1). 
  • A particularly active part of a fire. 
  • Checking the spread of fire at points of more rapid spread or special threat. Is usually the initial step in prompt control, with emphasis on first priorities. 
  • A stationary in-flight condition for helicopters when no directional flight is achieved. 
Hover Ceiling
  • Highest altitude above sea level at which a helicopter can hover at maximum computed gross weight. It is generally specified whether the quoted hover ceiling refers to hovering in ground effect (HIGE) or hovering out of ground effect (HOGE). 
Hover Hook-up
  • Attaching of a cargo lead line to a hovering helicopter. 
  • The process by which a helicopter fills a helibucket while hovering above the water source. 
Hovering in Ground Effect (HIGE)
  • The situation in which a helicopter is hovering sufficiently close to the ground to achieve added lift due to the effects of "ground cushion." The HIGE ceiling, for a given gross weight, thus is greater than the HOGE (Hovering Out of Ground Effect) ceiling.
Human-caused Fire
  • Any fire caused directly or indirectly by person(s). 
Human-caused Risk
  • Part of the National Fire Danger Rating System (NFDRS). A model for predicting the average number of reportable human caused fires from a given ignition component value. 
Human-caused Risk Scaling Factor
  • Part of the National Fire Danger Rating System (NFDRS). Number relating human-caused fire incidence to the ignition component in a fire danger rating area. It is based on three to five years of fire occurrence and fire weather data that adjusts the prediction of the basic human-caused fire occurrence model to fit local experience. 
  • Layer of decomposed organic matter on the forest floor beneath the fermentation layer and directly above the soil. It is that part of the duff in which decomposition has rendered vegetation unrecognizable and mixing of soil and organic matter is underway. 
  • Resistance to wetting exhibited by some soils, also called water repellency. The phenomenon may occur naturally or may be fire-induced. It may be determined by water drop penetration time, equilibrium liquid-contact angles, solid-air surface tension indices, or the characterization of dynamic wetting angles during infiltration. 
  • Recording instrument combining, on one paper record, the variation of dry-bulb temperature and relative humidity as a function of time.