National Fire Danger Rating System

National Fire Danger Rating System (NFDRS) is used in the United States to provide a measure of the relative seriousness of burning conditions and threat of fire.


John J. Keetch, a fire researcher in the southeast, wrote that "One of the prime objectives of the National Fire Danger Rating System (NFDRS) is to provide as accurate a measure as possible of the relative seriousness of burning conditions and thereby, NFDRS can serve as an aid to fire control programs."[1]

In 1954 there were eight different Fire danger rating systems in use across the United States. Better communication and better transportation were beginning to make mutual assistance agreements between fire control agencies more practical than in the past. State compacts, and in the case of the Federal government, interagency and interregional agreements were bringing fire control teams together from widely separated areas of the county. It became necessary to establish a national system for estimating Fire danger and fire behavior to improve and simplify communications among all people concerned with wildland fire.

Work on a national rating system began in 1959. By 1961, the basic structure for a four-phase rating system had been outlined and the fire phase (spread phase) was ready for field testing. However, since the remaining phases of the rating system - ignition, risk, and fuel energy - were not available, a number of fire control agencies preferred to remain with the systems then in use. Adaptations, interpretations, and additions to the spread phase quickly followed, making it obvious that the spread phase was not uniformly applicable across the country.

More research followed and in 1965 a research project headquartered in Seattle was established to provide a fresh look at the needs and requirements for a national, fire-danger, rating system. After canvassing many fire control agencies across the country, the Seattle research group recommended new directions for research that would lead to the development of a complete, comprehensive, National Fire-Danger Rating System. A target date of 1972 was established for getting a complete system ready for operational use.

In 1970, a preliminary version of the system was tested at field sites in Arizona and New Mexico. In 1971, an improved version of the system was used operationally in the Southwest. Field trials were also conducted elsewhere across the country at stations from Maine to California and from Florida to Alaska. The system then became operational nationwide in 1972.[2]

When work started in 1968 on the NFDRS a framework was constructed. A philosophy had to be adopted in order to allow the development of the system to proceed. NFDRS provides a uniform consistent system that possesses standards which agencies with wildfire suppression responsibility can apply and interpret.

NFDRS characterizes expected burning conditions for areas of 10,000 to 100,000 ac (4000 to 40,000 ha). The system has a low resolution.[3]

  • Considers initiating fires only.
  • Considers containment as opposed to extinguishment.
  • Relates containment job to flame length.
  • The ratings are to be interpretable and meaningful.
  • Ratings are to be used in combination.
  • Ratings are to be linear and relative.
  • Ratings between fuel models are comparable.
  • Ratings are for the worst case in the Fire Danger Rating Area.

Types of fires

NFDRS recognizes four types of fires:[4]

  1. Ground Fires burn in natural litter, duff, roots or sometimes high organic soils. Once started they are very difficult to detect and control.
  2. Surface Fires burn in grasses and low shrubs (up to 4.ft tall) or in the lower branches of trees. Surface fires may move rapidly. Ease of control depends upon the fuel involved.
  3. Crown Fires burn in the tops of trees. Once started, they are very difficult to control since wind plays an important role in crown fires.
  4. Spotting Fires can be produced by crown fires as well as wind and topography conditions. Large burning embers are thrown ahead of the main fire. Once spotting begins, the fire will be very difficult to control.


NFDRS is a complex set of equations with user-defined constants and measured variables to calculate the daily index and components that can be used for decision support.[3]

A Fire Danger Rating level.takes into account current and antecedent weather, fuel types, and live and dead fuel moisture [5]

Preparedness Classes

The bottom line of the National Fire Danger Rating System in the day-to-day operation of a fire prevention and suppression program is the staffing class. The staffing class is sometimes referred to as the action class, adjective class, precaution class, preparedness class, or the Industrial Fire Precaution Level (IFPL).[2]

The assumption behind staffing levels is that the continuum of fire danger can be divided into discrete intervals to which preplanned management actions are keyed. In other words, for each staffing level or adjective class, there should be a management action that addresses the dispatch of suppression resources that constitutes an appropriate level of response. Staffing levels, or adjective class ratings, are ways of linking fire danger information to fire management decisions. The designations for the various class or staffing levels are numerical (I to IV), or adjective (Low to Extreme).

The first step in establishing staffing levels is the selection by the state or federal land management agency of an NFDRS component or index that best describes the total fire problems in their protection area. Both state and federal land management agencies in Washington use the Energy Release Component (ERC) to determine staffing levels or adjective class ratings for the general public.

From statistical analysis of historical fire weather data, agencies were able to determine various percentiles in the distribution of historical ERC data that serve as breakpoints for various fire management decisions. Land management agencies in Washington use the 90th and 97th percentile of the ERC as a basis for determining staffing levels. In Western Washington, the 90th and 97th percentiles in the ERC frequency distribution are 44 BTUs per square foot and 55 BTUs per square foot.[2]


The output section of the NFDRS structure chart is the components or simply the outputs that are based in fire behavior description.but expressed in the broader context of fire danger rating.[6]

  1. Spread Component - Displays a value numerically equivalent to the predicted forward rate of spread of a head fire in feet per minute. It is a function of fuel model characteristics, live fuel moistures, the 0 to 3-inch (76 mm) dead fuel moisture (heavily weighted to the 1-hour timelag fuels), wind speed and slope class. It is highly variable from relative humidity, wind, and live fuel moisture.
  2. Ignition Component - Displays the probability of a firebrand causing an ignition requiring a suppression action.
  3. Keetch-Byram drought index
  4. Burning Index - An NFDRS index relating to the flame length at the head of the fire, it is an estimate of the potential difficulty of fire control as a function of how fast and how hot a fire could burn. It has been scaled so that the value, divided by 10, predicts the flame length at the head of a fire. For example, an index of 75 would predict a flame length of 7.5 feet (2.3 m). It is a function of the Spread Component and the Energy Release Component and has moderate variability. It is sensitive to fuel models.and can trace seasonal trends reasonably well for models with heavy dead or live components. Because it uses wind and relative humidity, it is also very sensitive to weather observation errors.[7]

Adjective Class Levels

Fire Danger is expressed using these levels.[8]

  1. LOW - Fuels do not ignite readily from small firebrands although a more intense heat source, such as lightning, may start fires in duff or light fuels.
  2. MODERATE - Fires can start from most accidental causes, but with the exception of lightning fires in some areas, the number of starts is generally low.
  3. HIGH - All fine dead fuels ignite readily and fires start easily from most causes.
  4. VERY HIGH - Fires start easily from all causes and, immediately after ignition, spread rapidly and increase quickly in intensity.
  5. EXTREME - Fires start quickly, spread furiously, and burn intensely. All fires are potentially serious.


Each day during the fire season, national maps of selected fire weather and Fire danger components of the National Fire Danger Rating System are produced by the Wildland Fire Assessment System (WFAS-MAPS), located at the USDA Forest Service Rocky Mountain Research Station in Missoula, Montana. Current fire danger and forecast fire danger maps are available.[9]


  1. ^ Keetch, John J; Byram, George. 1968. A drought index for forest fire control. Res. Paper SE-38. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station. 32 pp. (Revised 1988).
  2. ^ a b c National Fire Danger Rating System (NFDRS) / John Wiley & Sons, Inc.
  3. ^ a b Burgan, Robert E. 1988. 1988 revisions to the 1978 National Fire-Danger Rating System. Res. Pap. SE-273. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station. 39 pp.
  4. ^
  5. ^ (Deeming and others 1977, Bradshaw and others 1984).
  6. ^
  7. ^
  8. ^ Gaining and Understanding of the National Fire Danger Rating System. NWCG PMS 932 July 2002
  9. ^ WFAS - Wildland Fire Assessment System

External links

Burning Index

Burning Index (BI) is a number used by the National Oceanic and Atmospheric Administration (NOAA) to describe the potential amount of effort needed to contain a single fire in a particular fuel type within a rating area. The National Fire Danger Rating System (NFDRS) uses a modified version of Bryam's equation for flame length - based on the Spread Component (SC) and the available energy (ERC) - to calculate flame length from which the Burning Index is computed.

The equation for flame length is listed below:


j is a scaling factor,
SC is the spread component,
and ERC is the Energy Release Component.

Consequently, the equation for the Burning Index is:

where is the Burning Index scaling factor of (10/ft). Therefore, dividing the Burning Index by 10 produces a reasonable estimate of the flame length at the head of a fire. A unique Burning Index (BI) table is required for each fuel model.

Chain (unit)

The chain is a unit of length equal to 66 feet (22 yards). It is subdivided into 100 links or 4 rods. There are 10 chains in a furlong, and 80 chains in one statute mile. In metric terms, it is 20.1168 m long. By extension, chainage (running distance) is the distance along a curved or straight survey line from a fixed commencing point, as given by an odometer.

The chain has been used for several centuries in England and in some other countries influenced by English practice. In the United Kingdom, there were 80 chains to the mile, but until the early nineteenth century the Scottish and Irish customary miles were longer than the statute mile; consequently a Scots chain was about 74 (imperial) feet, an Irish chain 84 feet. These longer chains became obsolete following the adoption of the imperial system in 1824. This unit ceased to be permitted to be "used for trade" in 1985.

Energy release component

The energy release component (ERC) is a number related to the available energy (BTU) per unit area (square foot) within the flaming front at the head of a fire. Daily variations in ERC are due to changes in moisture content of the various fuels present, both live and dead. Since this number represents the potential "heat release" per unit area in the flaming zone, it can provide guidance to several important fire activities. It may also be considered a composite fuel moisture value as it reflects the contribution that all live and dead fuels have to potential fire intensity. The ERC is a cumulative or "build-up" type of index. As live fuels cure and dead fuels dry, the ERC values get higher, thus providing a good reflection of drought conditions. The scale is open-ended or unlimited and, as with other NFDRS components, is relative. Conditions producing an ERC value of 24 represent a potential heat release twice that of conditions resulting in an ERC value of 12.

Forest fire weather index

The Forest fire weather index (FWI) (French: indice forêt météo, IFM) is an estimation of the risk of wildfire computed by Météo France and the Meteorological Service of Canada. It was introduced in France in 1992 but is based on a Canadian empirical model developed and widely used since 1976.

Fuel model

A Fuel Model is a stylized set of fuel bed characteristics used as input for a variety of wildfire modeling applications. Wildfire behavior models, such as those of Rothermel, take into account numerous empirical variables. While these inputs are important for equation outputs, they are often difficult and time-consuming, if not impossible, to measure for each fuel bed. A fuel model defines these input variables for a stylized set of quantitative vegetation characteristics that can be visually identified in the field. Depending on local conditions, one of several fuel models may be appropriate. As Anderson states “Fuel models are simply tools to help the user realistically estimate fire behavior. The user must maintain a flexible frame of mind and an adaptive method of operating to totally utilize these aids". Furthermore, depending on the application, the user must choose a fuel model classification system. The major classification systems for use in the United States include the National Fire Danger Rating System, the 13 ‘original’ fuel models of Anderson and Albini, the subsequent set of 40 fuels produced by Scott and Burgan, and the Fuel Characteristics Classification System.

Glossary of firefighting

Note: This list does not include firefighting equipment, i.e., tools and apparatus used by firefighters. Please refer to Glossary of firefighting equipment for such terms. Similarly, although there is much overlap, you may also want to refer to the Glossary of wildfire terms for terminology particular to that type of firefighting.

Note: Many of the terms defined here, particularly relating to systems of work, team names, procedures, careers and policies, seem to originate in the U.S. and are not necessarily applicable to other English-speaking countries' fire and rescue services. For example, Call Firefighter (U.S.) and Retained Firefighter (UK).Firefighting jargon includes a diverse lexicon of both common and idiosyncratic terms. One problem that exists in trying to create a list such as this is that much of the terminology used by a particular department is specifically defined in their particular standing operating procedures, such that two departments may have completely different terms for the same thing. For example, depending on whom one asks, a safety team may be referred to as a standby, a RIT or RIG or RIC (rapid intervention team/group/crew), or a FAST (firefighter assist and search team). Furthermore, a department may change a definition within its SOP, such that one year it may be RIT, and the next RIG or RIC.

The variability of firefighter jargon should not be taken as a rule; some terms are fairly universal (e.g. stand-pipe, hydrant, chief). But keep in mind that any term defined here may be department- or region-specific, or at least more idiosyncratic than one may realize.

Glossary of wildfire terms

The following is a glossary of wildfire terms. Except where noted, terms are taken from a 1998 Fireline Handbook transcribed for a Conflict 21 counter-terrorism studies website by the Air National Guard.Separate glossaries for firefighting terms and firefighting equipment are also available.

Incident management team

Incident management team (IMT) is a term used in the United States of America to refer to a group that responds to an emergency. Although the primary purpose of an incident management team is for wildfire response, an IMT can respond to a wide range of emergencies, including fires, floods, earthquakes, hurricanes, tornadoes, tsunami, riots, spilling of hazardous materials, and other natural or human-caused incidents.

In the United States, there are predominantly five types of incident management teams (IMTs). An incident such as a wildland fire is initially managed by local fire departments or fire agencies, but if the fire becomes complex additional resources are called in to address the emergency, and higher levels of management training and capability are required. IMTs are "typed" according to the complexity of incidents they are capable of managing and are part of an incident command system.

To manage the logistical, fiscal, planning, operational, safety and community issues related to the incident/emergency, an Incident Management Team will provide the command and control infrastructure that is required.

Incident management starts as the smallest unit and escalates according to the complexity of the emergency. The five types of IMTs are as follows:

Type 5: Local Village and Township Level – a "pool" of primarily fire officers from several neighboring departments trained to serve in Command and General Staff positions during the first 6–12 hours of a major or complex incident.

Type 4: City, County or Fire District Level – a designated team of fire, EMS, and possibly law enforcement officers from a larger and generally more populated area, typically within a single jurisdiction (city or county), activated when necessary to manage a major or complex incident during the first 6–12 hours and possibly transition to a Type 3 IMT.

Type 3: State or Metropolitan Area Level – a standing team of trained personnel from different departments, organizations, agencies, and jurisdictions within a state or DHS Urban Area Security Initiative (UASI) region, activated to support incident management at incidents that extend beyond one operational period. Type 3 IMTs will respond throughout the state or large portions of the state, depending upon State-specific laws, policies, and regulations.

Type 2: National and State Level – a federally or state-certified team; has less training, staffing and experience than Type 1 IMTs, and is typically used on smaller scale national or state incidents. There are thirty-five Type 2 IMTs currently in existence, and operate through interagency cooperation of federal, state and local land and emergency management agencies.

Type 1: National and State Level – a federally or state-certified team; is the most robust IMT with the most training and experience. Sixteen Type 1 IMTs are now in existence, and operate through interagency cooperation of federal, state and local land and emergency management agencies.An incident management team consists of five subsystems as follows:

Incident command system (ICS) – an on-scene structure of management-level positions suitable for managing any incident;

Training – including needs identification, development, and delivery of training courses;

Qualifications and certification – the United States has national standards for qualifications and certification for ICS positions;

Publications management – the development, control, sourcing, and distribution of National Incident Management System (NIMS) publications provided by the National Wildfire Coordinating Group (NWCG); and

Supporting technology and systems – technology and materials used to support an emergency response, such as Geographic Information Systems (GIS), orthophoto mapping, National Fire Danger Rating System, remote automatic weather stations, automatic lightning detection systems, infrared technology, and communications.

Keetch–Byram drought index

The Keetch–Byram drought index (KBDI), created by John Keetch and George Byram in 1968 for the United States Department of Agriculture's Forest Service, is a measure of drought conditions. It is commonly used for the purpose of predicting the likelihood and severity of wildfire. It is calculated based on rainfall, air temperature, and other meteorological factors.

The KBDI is an estimate of the soil moisture deficit, which is the amount of water necessary to bring the soil moisture to its full capacity. A high soil moisture deficit means there is little water available for evaporation or plant transpiration. This occurs in conditions of extended drought, and has significant effects on fire behaviour.

In the United States, it is expressed as a range from 0 to 800, referring to hundredths of an inch of deficit in water availability; in countries that use the metric system, it is expressed from 0 to 200, referring to millimetres.

National Weather Service

The National Weather Service (NWS) is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the purposes of protection, safety, and general information. It is a part of the National Oceanic and Atmospheric Administration (NOAA) branch of the Department of Commerce, and is headquartered in Silver Spring, Maryland, within the Washington metropolitan area. The agency was known as the United States Weather Bureau from 1890 until it adopted its current name in 1970.The NWS performs its primary task through a collection of national and regional centers, and 122 local Weather Forecast Offices (WFOs). As the NWS is an agency of the U.S. federal government, most of its products are in the public domain and available free of charge.

Spread Component

Spread Component (SC) (as used in the National Fire Danger Rating System) is a rating of the forward rate of spread of a headfire. Deeming states that "the spread component is numerically equal to the theoretical ideal rate of spread expressed in feet-per-minute."

This carefully worded statement indicates both guidelines (theoretical) and cautions (ideal) that must be used when applying the spread component. Wind speed, slope, and fine fuel moisture are key inputs in the calculations of the spread component, thus accounting for a high variability from day to day. The spread component is expressed on an open-ended scale; it has no upper limit.


A wildfire or wildland fire is a fire in an area of combustible vegetation occurring in rural areas. Depending on the type of vegetation present, a wildfire can also be classified more specifically as a brush fire, bushfire, desert fire, forest fire, grass fire, hill fire, peat fire, vegetation fire, and veld fire.Fossil charcoal indicates that wildfires began soon after the appearance of terrestrial plants 420 million years ago. Wildfire's occurrence throughout the history of terrestrial life invites conjecture that fire must have had pronounced evolutionary effects on most ecosystems' flora and fauna. Earth is an intrinsically flammable planet owing to its cover of carbon-rich vegetation, seasonally dry climates, atmospheric oxygen, and widespread lightning and volcanic ignitions.Wildfires can be characterized in terms of the cause of ignition, their physical properties, the combustible material present, and the effect of weather on the fire. Wildfires can cause damage to property and human life, though naturally occurring wildfires may have beneficial effects on native vegetation, animals, and ecosystems that have evolved with fire. High-severity wildfire creates complex early seral forest habitat (also called "snag forest habitat"), which often has higher species richness and diversity than unburned old forest. Many plant species depend on the effects of fire for growth and reproduction. Wildfires in ecosystems where wildfire is uncommon or where non-native vegetation has encroached may have strongly negative ecological effects. Wildfire behavior and severity result from the combination of factors such as available fuels, physical setting, and weather. Analyses of historical meteorological data and national fire records in western North America show the primacy of climate in driving large regional fires via wet periods that create substantial fuels or drought and warming that extend conducive fire weather.Strategies for wildfire prevention, detection, and suppression have varied over the years. One common and inexpensive technique is controlled burning, intentionally igniting smaller fires to minimize the amount of flammable material available for a potential wildfire. Vegetation may be burned periodically to maintain high species diversity and limit the accumulation of plants and other debris that may serve as fuel. Wildland fire use is the cheapest and most ecologically appropriate policy for many forests. Fuels may also be removed by logging, but fuels treatments and thinning have no effect on severe fire behavior when under extreme weather conditions. Wildfire itself is reportedly "the most effective treatment for reducing a fire's rate of spread, fireline intensity, flame length, and heat per unit of area" according to Jan Van Wagtendonk, a biologist at the Yellowstone Field Station. Building codes in fire-prone areas typically require that structures be built of flame-resistant materials and a defensible space be maintained by clearing flammable materials within a prescribed distance from the structure.

Wildfire suppression

Wildfire suppression is a range of firefighting tactics used to suppress wildfires. Firefighting efforts in wild land areas require different techniques, equipment, and training from the more familiar structure fire fighting found in populated areas. Working in conjunction with specially designed aerial firefighting aircraft, these wildfire-trained crews suppress flames, construct fire lines, and extinguish flames and areas of heat to protect resources and natural wilderness. Wildfire suppression also addresses the issues of the wildland-urban interface, where populated areas border with wild land areas.

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