National Fire Danger Rating System

This is the NFDRS Fire Index used by the National Forest Service for:
100101 - BONNERS
Bonners Ferry, Idaho
elev. - 2320    lat. * 48.7    long. * -116.2
Observed    10-Apr-21
ERC - 37    BI - 46    SC - 10    STL - 3    IC - 9
fire sign

Forecast    11-APR-21
ERC - 43    BI - 43    SC - 8    STL - 3    IC - 21
fire sign
map loc

The National Fire Danger Rating System (NFDRS) is the best method to forecast the real fire danger which uses the Energy Release Component (ERC) or the Burn Index (BI). Some stations use ERC and others use BI for calculating the Fire Danger Rating. They have a chart that uses Staffing Levels (STL or SL) and the Ignition Component (IC) to derive the Adjective Fire Ratings of Low, Moderate, High, Very High, and Extreme.


Less than 50

Fuels do not ignite readily from small firebrands although a more intense heat source, such as lightning, may start fires in duff or punky wood. Fires in open cured grasslands may burn freely a few hours after rain, but woods fires spread slowly by creeping or smoldering, and burn in irregular fingers. There is little danger of spotting.

50 to 75

Fires can start from most accidental causes but, with the exception of lightning fires in some areas, the number of starts is generally low. Fires in open cured grasslands will burn briskly and spread rapidly on windy days. Timber fires spread slowly to moderately fast. The average fire is of moderate intensity, although heavy concentrations of fuel, especially draped fuel, may burn hot. Short-distance spotting may occur, but is not persistent. Fires are not likely to become serious and control is relatively easy.

75 to 90

All fine dead fuels ignite readily and fires start easily from most causes. Unattended brush and campfires are likely to escape. Fires spread rapidly and short-distance spotting is common. High-intensity burning may develop on slopes or in concentrations of fine fuels. Fires may become serious and their control difficult unless they are attacked successfully while small

90 to 97.5

Fires start easily from all causes and, immediately after ignition, spread rapidly and increase quickly in intensity. Spot fires are a constant danger. Fires burning in light fuels may quickly develop high intensity characteristics such as long-distance spotting and fire whirlwinds when they burn into heavier fuels.

Above 97.5

Fires start quickly, spread furiously, and burn intensely. All fires are potentially serious. Development into high intensity burning will usually be faster and occur from smaller fires than in the very high fire danger class. Direct attack is rarely possible and may be dangerous except immediately after ignition. Fires that develop headway in heavy slash or in conifer stands may be unmanageable while the extreme burning condition lasts. Under these conditions the only effective and safe control action is on the flanks until the weather changes or the fuel supply lessens.

NFRDS Data Legend

ERC = Energy Release Component - 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.

BI = Burning Index - 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.

SC = Spread Component - 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.

STL or SL = Staffing Level - 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.

IC = Ignition Component - 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.

The Adjective Class Fire Danger Rating should only be utilized for public information. Staffing Level (SL or STL) is used for in-house fire readiness. The actual determination of the daily adjective rating is based on the current or predicted value for a user selected staffing index and ignition component using the table below.

Staffing Levels (SL or STL) Adjective Fire Danger Rating (R)
1-, 1, 1+LL LMM
2-, 2, 2+LM MMH
3-, 3, 3+MM HHVH
4-, 4, 4+MH VHVHE
5-, 5, 5+HVH VHEE
Ignition Component0 - 20 21 - 4546 - 6566 - 80 81 - 100

Script courtesy of Alan Clark at N5PA    Modified by John Shortt at Apache Junction Weather