Common terms - National Fire Danger Rating System (NFDRS)
Ignition Component (IC) - Related to the probability of a firebrand producing a fire that will require
suppression action. It is mainly a function of the 1 hour time lag (fine fuels) fuel moisture content and
the temperature of the receptive fine fuels. IC has no units. A percentage of probability from 1-100.
Spread Component (SC) - A rating of the forward rate of spread of a head fire. It integrates the effect of wind, slope, and fuel bed and fuel particle properties. The daily variations are caused by the changes in the wind and moisture contents of the live fuels and the dead fuel timelag classes of 1, 10, and 100 hr.
Energy Release Component (ERC) - Based upon the estimated potential available energy released per
unit area in the flaming zone of a fire. It is dependent upon the same fuel characteristics as the spread
component (SC). The day to day variations of the ERC are caused by changes in the moisture contents
of the various fuel classes, including the 1000 hour time lag class. ERC is derived from predictions of
the rate of heat release per unit area during flaming combustion and the duration of the burning.
Expressed in BTU's per square foot.
Burning Index (BI) - A measure of fire intensity. BI combines the Spread Component and Energy
Release Component to relate to the contribution of fire behavior to the effort of containing a fire. BI has
no units, but in general it is 10 times the flame length of a fire.
Fire Load Index (FL) - A rating of the maximum effort required to contain all probable fires occurring
within a rating area during the rating period. It is the cumulative index of the NFDRS. It is designed to
combine the projections of fire occurrence and behavior into a single number that can be related to the
total fire suppression job. The meaning of FL has been left to the user. By itself, it does not tell the user
much about the nature of the fire management problem. One needs to examine the individual
components and indices that are the basis for the FL. It ranges over a scale of 1-100 and has no units.
Staffing Level (SL) - A component of the NFDRS relating to the level of fire management staffing. Staffing levels are from 1-5 with 1 being the lowest and 5 the highest.
Adjective Rating (R) - A public information component of the NFDRS specific to the rating of fire
danger. Adjective ratings are: low(L), moderate(M), high(H), very high(V) and extreme(E).
Keetch-Byram Drought Index (KBDI) - A number between 0-800 representing the amount of moisture
in the top 8 inches of soil. Zero is saturated, 800 is maximum drought stress. It is calculated from recent
precipitation measurements in relation to the average annual precipitation. It is important to note that the
KBDI is customized for each geographic area and that often the scale shows less of a range in variation.
Fire Danger Rating - A fire management system that integrates the effects of selected fire danger
factors into one or more qualitative or numerical indices of current protection needs.
Haines Index - A national fire-weather index based on the stability and moisture content of the lower
atmosphere and their direct relationship to the growth of large fires. The index is from 1-6 with 1 being
the lowest potential for large plume-doominated fires, while 6 is the highest potential for plume-dominated fires.
Lightning Activity Level (LAL) - A numerical rating from the lowest of 1 to the highest of 6, keyed to the
start of thunderstorms and the frequency and character of cloud-to-ground lighting forecasted or
observed on a rating area during a rating period.
National Fire Danger Rating System (NFDRS) - A multiple index system developed to provide
information about current and predicted fire danger conditions.
Remote Automated Weather Station (RAWS) - A special remote fire weather observation station
which takes timed measurements of the various weather factors used to calculate fire danger and
behavior. These stations usually transmit data via satellite telemetry to the National Interagency Fire
Center for distribution to fire managers nation-wide.