National Fire Danger Rating System

The National Fire danger Rating System is a set of computer programs and algorithms that allow land management agencies to estimate today's or tomorrow's fire danger for a given rating area. NFDRS characterizes fire danger by evaluating the approximate upper limit of fire behavior in a fire danger rating area during a 24-hour period. Calculations of fire behavior are based on fuels, topography and weather, or what is commonly called the fire triangle. NFDRS output give relative ratings of the potential growth and behavior of any wildfire. Fire danger ratings are guides for initiating presuppression activities and selecting the appropriate level of initial response to a reported wildfire in lieu of detailed, site- and time-specific information. It links an organization's readiness level (or pre-planned fire suppression actions) to the fire problems of the day.

In 1954 there were eight different fire-danger rating systems in use across the county. 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 fires.

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 a 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.

The philosophy of the National Fire Danger Rating System can be summarized as follows:

The basic structure of the system provides three indexes.... (Occurrence Index, Burning Index, and the Fire Load Index).... designed to aid in planning fire control activities on a fire protection unit. These indexes are derived from three fire behavior components - Spread Component(SC), Energy Release Component (ERC), and the Ignition Component (IC). The scale for each index runs from 0 to 100. Click on the appropriate box below to view further discussion on the various indexes and components.

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).

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 through 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. 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.

Fire Danger Maps

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 forecasted fire danger maps are available by using the links listed below.