National Fire Danger Rating System Description
- Low. Fuels do not ignite
readily from small firebrands, although a more intense *-heat-* source,
such as lightning, may start many fires in duff or punky wood. Fires
in open cured grassland 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.
The color code for Low is green
- 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. Fires in
open-cured grassland will burn briskly and spread rapidly on windy
days. Woods 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.
The color code for Moderate is blue.
- High. 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, in concentrations of fine fuel. Fires may become serious
and their control difficult, unless they are hit hard and fast while
small.The color code for High is yellow.
- Very High.
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. Direct attack at the head of such
fires is rarely possible after they have been burning more than a few
The color code for Very High is orange.
- Extreme. Fires
under extreme conditions 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 danger class (item 4). 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.
The color code for Extreme is red.
Source: Forest Service Handbook, February 1964
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