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)
  • A magnetic bearing extending from a ground-based navigational system, providing airborne navigation information. 
Radiant Burn
  • A thermal trauma that maybe a superficial, partial thickness or full thickness burn. 
Radiant Heat Flux
  • The amount of heat flowing through a given area in a given time, usually expressed as calories/square centimeter/second. 
  1. Propagation of energy in free space by virtue of joint, undulatory variations in the electric or magnetic fields in space, (i.e., by electromagnetic waves).
  2. Transfer of heat in straight lines through a gas or vacuum other than by heating of the intervening space. 
Radio Cache
  • A cache may consist of a number of portable radios, base station, and, in some caches, a radio repeater that is stored in a predetermined location for dispatch to incidents. 
Radio Fix
  • Determination of position by one or more radio navigational aids. 
  • A device carried aloft by a balloon equipped with measuring instruments that automatically convert temperature, pressure, and humidity data into electrical impulses and transmit this information to a ground recorder.
Railroad Fire
  • A fire resulting from any operation or activity of a railroad, except smoking. 
Range Fire
  • Any wildfire on rangeland. 
  • Technique of landing specifically trained and certified firefighters from hovering helicopters; involves sliding down ropes with the aid of friction-producing devices. 
Rate of Spread
  • The relative activity of a fire in extending its horizontal dimensions. It is expressed as rate of increase of the total perimeter of the fire, as rate of forward spread of the fire front, or as rate of increase in area, depending on the intended use of the information. Usually it is expressed in chains or acres per hour for a specific period in the fire's history.
Rate of Spread Factor
  • A factor usually on a scale of 1 to 100 which represents a relative rate of forward spread for a specific fuel condition and fixed weather conditions (or fuel model). Factors can be used as multipliers, arguments for entering tables, or provide a ratio of values between two fuels. 
Rate of Spread Meter
  • A device that computes the probable rate of spread of a fire for different combinations of fuel moisture, wind speed, and other selected factors. 
Rating Period
  • Part of the National Fire Danger Rating System (NFDRS). The period of time during which a fire danger rating value is considered valid or representative for administrative or other purposes. Normally it is 24 hours extending from midnight to midnight. 
  • Method of upper-air observation consisting of an evaluation of the wind speed and wind direction, temperature, pressure, and relative humidity aloft by means of a balloon-borne radiosonde tracked by a radar or radio direction-finder. 
  • Confirmation through the re-issuance of an incident qualification card that an individual has regained qualifications for a specified position that was lost through a lack of current experience. A key component in the certification or re-certification process is the subjective evaluation by the appropriate agency official of an individual's capability to perform in a position. 
Reaction Intensity
  • The rate of heat release, per unit area of the flaming fire front, expressed as heat energy/area/time, such as Btu/square foot/minute, or Kcal/square meter/second.
  1. Condition or degree of being completely ready to cope with a potential fire situation.
  2. Mental readiness to recognize changes in fire danger and act promptly when action is appropriate. 
Rear (Of a Fire)
  1. That portion of a fire spreading directly into the wind or down slope.
  2. That portion of a fire edge opposite the head.
  3. Slowest spreading portion of a fire edge. Also known as a heel of a fire. 
Reason For Responding To Incident On Unprotected Land
  • The rationale an agency responded to an incident where the point of origin is on unprotected land.
    • Business Rule:  A user can select from just one value - Threat. The responding organization determines threat to protected lands.
Reasonably Available Control Measures (RACM)
  • Control measures developed by EPA which apply to residential wood combustion, fugitive dust, and prescribed and silvicultural burning in and around "moderate" PM-10 non-attainment areas. RACM is designed to bring an area back into attainment and uses a smoke management program which relies on weather forecasts for burn/no-burn days. 
  1. Repeat burning of an area over which a fire has previously passed, but left fuel that later ignites when burning conditions are more favorable.
  2. An area that has reburned. 
Reconnaissance (RECON)
  • To examine a fire area to obtain information about current and probable fire behavior and other related fire suppression information. 
  • Individuals within ICS organizational units who are responsible for recording information. Recorders may be found in planning, logistics and finance/administration units. 
  1. The increase in fuel moisture as a result of increased relative humidity, usually occurring overnight.
  2. The general term used to describe the maximum overnight value of atmospheric relative humidity. 
Recreation Fire
  • A fire resulting from recreational use, except smoking. 
Recurrent Training
  • Training scheduled at established intervals that has been identified as required training in order to maintain position currency. 
Red Flag Warning
  • Term used by fire weather forecasters to alert forecast users to an ongoing or imminent critical fire weather pattern.
  • A frame on which hose is wound, now chiefly used for "booster" or small hose (3/4- or l-inch hose) (19 or 25 mm) supplied by a water tank on the apparatus; also, a hand-drawn 2-wheel frame for 2-1/2 inch (64 mm) hose used in industrial plants. 
Reference Point(s)
Regional Haze
  • Visibility impairment caused by the cumulative air pollutant emissions from numerous sources over a wide geographic area. 
Regular Government Employee
  • Includes any individual hired under authorities other than the AD Pay Plan for Emergency Workers. Federal general schedule and federal wage system employees are included in this category.
  • Efforts undertaken within three years of a wildland fire to repair or improve fire damaged lands unlikely to recover to a management approved conditions or to repair or replace minor facilities damaged by fire.
  • Re-ignition due to latent heat, sparks, or embers or due to presence of smoke or steam. 
Relative Greenness (RG)
  • An NDVI-derived image of vegetation greenness compared to how green it has been historically.
Relative Humidity (RH)
  • The ratio of the amount of moisture in the air, to the maximum amount of moisture that air would contain if it were saturated. The ratio of the actual vapor pressure to the saturated vapor pressure.  Source:  http://glossary.ametsoc.org/wiki/Relative_humidity
  • Use of two or more fire pumps to move water a distance which would require excessive pressures in order to overcome friction loss if only one pump were employed at the source. 
Relay Tank
  • A tank, usually collapsible, used as a reservoir in the relay of water from one fire pump to another. 
Relief Valve
  • A pressure-controlled device which bypasses water at a fire pump to prevent excessive pressures when a nozzle is shut down. 
Reload Base
  • An airfield where airtankers are reloaded but not permanently stationed. 
Remote Automatic Weather Station (RAWS)
  • A weather station that transmits weather observations via GOES satellite to the Wildland Fire Management Information system. 
  • A radio signal station that automatically relays a radio transmission, sometimes over a different frequency, thereby increasing the range of transmission. Repeaters are often named for the mountaintops or peaks where they are installed. 
Report Time
  • Elapsed time from fire discovery until the first personnel charged with initiating action for fire suppression are notified of its existence and location. 
Reportable Fire
  • Any wildfire that requires fire suppression to protect natural resources or values associated with natural resources, or is destructive to natural resources. 
Reporting Locations
  • Location or facilities where incoming resources can check-in at the incident. Check-in locations include: incident command post (resources unit), incident base, camps, staging areas, helibases, helispots, and direct to the line. Check-in at one location only. 
Reporting Unit
  • The entity submitting a given incident report.
    • Definition Extension:  The entity must have a valid NWCG Unit Identifier (ID).
Request Number (Resource Order Number)
  • As resources are ordered to respond to an incident, Request Numbers (occasionally referred to as a resource order number) are issued. The order number includes the incident number, an alpha character (S = Supplies, E = Equipment, O = Overhead, A = Aircraft, C = Crews, M = Agency Provided Medical Care) followed by a sequential number.
Required Experience
  • Documented, satisfactory performance in a specified position needed to qualify for another (usually higher level) position. Required experience cannot be challenged. 
Required Training
  • A course or courses that must be completed prior to initiating a position task book. Training which has been identified as required cannot be challenged; an agency equivalent course may be used as a substitute when the course meets or exceeds a required course's learning and performance objectives. 
  • Saving a life from fire or accident; removing a victim from an untenable or unhealthy atmosphere. 
Rescue Medical
  • Any staffed ground vehicle capable of providing medical services. 
Rescue Medical Vehicle
  • Any staffed ground vehicle capable of providing emergency medical care and staffed with appropriate number of trained personnel and equipment for that incident. 
Residence Time
  • The time, in seconds, required for the flaming front of a fire to pass a stationary point at the surface of the fuel. The total length of time that the flaming front of the fire occupies one point. 
Residual Combustion Stage
  • The smoldering zone behind the zone of an advancing fire front. 
Residual Smoke
  • Smoke produced by smoldering material. The flux of smoke originating well after the active flaming combustion period with little or no vertical buoyancy and, therefore, most susceptible to subsidence inversions and down-valley flows. 
  • At a general level used to refer to the ability of a system (ecological or human) to resist damage and recover from a disturbance. In ecology, resiliency tends to refer to the ability of the system to return to the pre disturbance state with no assessment of whether that state is desirable or not. From a social perspective, resilience may reference ability to return to the original state but also can refer to the ability to recover to a state more likely to resist or recover quickly from future disturbance.
Resistance to Control
  • The relative difficulty of constructing and holding a control line as affected by resistance to line construction and by fire behavior. Also known as difficulty of control. 
Resistance to Line Construction
  • The relative difficulty of constructing control line as determined by the fuel, topography, and soil. 
Resource Capability
  • The ability of the wildland fire program to respond to current and anticipated workload needs for the area of concern. 
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. 
Resource Ordering and Status System (ROSS)
  • A national system that provides automated support to interagency and agency dispatch and coordination offices. The system will provide current status of resources available to support all-risk activities; enable dispatch offices to exchange and track resource ordering information electronically; enable dispatch offices to rapidly and reliably exchange mission-critical emergency electronic messages. 
Resource Value-at-risk
  • Fire suppression planning tool providing a relative expression (in five classes) of fire effects on all resources (not the value of the resources themselves). 
  1. Personnel, equipment, services and supplies available, or potentially available, for assignment to incidents. Personnel and equipment are described by kind and type, e.g., ground, water, air, etc., and may be used in tactical, support or overhead capacities at an incident.
  2. The natural resources of an area, such as timber, grass, watershed values, recreation values, and wildlife habitat.
Resources Unit
  • Functional unit within the planning section responsible for recording the status of resources committed to the incident. The unit also evaluates resources currently committed to the incident, the impact that additional responding resources will have on the incident, and anticipated resource needs. 
  • A simple filter mask for individual protection against smoke and fumes, recommended for use in fire suppression on wildfires only; not recommended for use on structure fires or fires involving most hazardous materials. 
Responding Unit
  • Administrative entity that provides resources in response to the incident.
    • Definition Extension:  The entity must have a valid NWCG Unit Identifier (ID).
      • Not the type of resource responding.
      • Not limited to Jurisdictional or Protecting Units (contractors, volunteer fire departments, military resources, etc.)
Responsible Fire Agency
Restricted Airspace
  • Airspace of defined dimensions identified by an area on the surface of the earth within the flight of an aircraft, which is subject to restrictions (but not wholly prohibited). 
Restricted Category
  • Aircraft that is generally used for cargo, retardant dropping, agricultural operations, survey work and other specific projects, and may not transport passengers. 
  • Measures taken by jurisdictional agencies to impose bans and standards of use on certain human activities that could lead to the cause of wildland fire. Restrictions may be applied to: smoking in designated areas; open flame; mechanical operations in high-risk areas; and off-road use.
  • A substance or chemical agent which reduces the flammability of combustibles. 
Retardant Base
  • Ground facilities for mixing, storing, and loading fire retardant into airtankers. 
Retardant Coverage
  • Area of fuel covered and degree of coverage on the fuel by a fire retardant, usually expressed in terms of gallons per hundred square feet (liters per square meter). 
Retardant Drop
  • Fire retardant cascaded from an airtanker or helitanker. 
Return and Hold
  • An order to an airtanker pilot to return to the retardant base and await further instructions; mission completed, further loads not required. 
Reversible Siamese (SIMWYE)
  • Hose fitting that performs the functions of a Siamese or a wye (i.e., to combine the flow from two lines into a single line or to permit two lines to be taken from a single line).
Rheologic Properties
  • Flow characteristics of liquid fire retardants, especially their cohesiveness or ability to hold together while falling through the air. 
  • Science of deformation and flow of fire retardants and other liquids, especially of the cohesiveness bodies and stress-strain relationship of their particles. 
Rich Tool
  • A long-handled combination rake and cutting tool, the blade of which is constructed of a single row of mowing machine cutter teeth fastened to a piece of angle iron. Also known as a fire rake or council rake.
Right Angle Transect
Ring Fire
  • A fire started by igniting the full perimeter of the intended burn area so that the ensuing fire fronts converge toward the center of the burn. Set around the outer perimeter of a resource to establish a protective black-line-buffer. 
  1. The chance of fire starting as determined by the presence and activity of causative agents.
  2. A chance of suffering harm or loss.
  3. A causative agent.
  4. (NFDRS) A number related to the potential of firebrands to which a given area will be exposed during the rating day. 
Risk Assessment
Risk Index
  • A number related to the probability of a firebrand igniting a fire. 
Risk Management (RM)
  • A continuous, five-step process that provides a systematic method for identifying and managing the risks associated with any operation. 
Risk Source
  • Identifiable human activity that historically has been a major cause of wildfires on a protection unit; one of the eight general causes listed on the standard fire report. 
Risk Source Ratio
  • Portion of human-caused fires that have occurred on a protection unit chargeable to a specific risk source; calculated for each day of the week for each risk source. 
Rocker Lug Coupling
  • Hose coupling in which the lugs used for tightening or loosening are semicircular in shape and designed to pass over obstructions. 
Roll Cloud
  • A turbulent altocumulus-type cloud formation found in the lee of some large mountain barriers. The air in the cloud rotates around an axis parallel to the range. Also sometimes refers to part of the cloud base along the leading edge of a cumulonimbus cloud; it is formed by rolling action in the wind shear region between cool downdrafts within the cloud and warm updrafts outside the cloud. Also known as a rotor cloud.  Source:  http://glossary.ametsoc.org/wiki/Roll_cloud
  • Assembly of airfoils (rotor blades), together with a hub and attachments, that rotates about an axis to provide lift and/or thrust on a helicopter. 
Rotor Blast
  • Air turbulence occurring under and around the main rotor of an operating helicopter. Also known as a rotor downwash. 
Rotor Diameter
  • The main rotor arc in feet and inches (meters). Used for planning helispot clearance. 
  • The accumulation of living and dead ground and understory vegetation, especially grasses, forest litter, and draped dead needles, sometimes with addition of underbrush such as palmetto, gallberry, and wax myrtle. Most often used for southern pine types. 
Rough Reduction
  • Reduction of fire hazard in rough, usually by prescribed burning. 
Run (Of a Fire)
  • Rapid advance of the head of a fire, characterized by a marked transition in fireline intensity and rate of spread with respect to that noted before and after the advance. 
Running Fire
  • Behavior of a fire spreading rapidly with a well defined head. 
  • Any area wherein residences and other developments are scattered and intermingled with forest, range, or farm land and native vegetation or cultivated crops. 
Rural Fire District (RFD)
  • An organization established to provide fire protection to a designated geographic area outside of areas under municipal fire protection. Usually has some taxing authority and officials may be appointed or elected. 
Rural Fire Protection
  • Fire protection and firefighting problems that are outside of areas under municipal fire prevention and building regulations and that are usually remote from public water supplies.