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The interagency fire community in Alaska utilizes the Canadian forest fire danger
rating system, commonly referred to as CFFDRS, for both fire danger and for
fire behavior predictions.
CFFDRS is a systematic method of assessing wildland fire behavior potential
It is a series of mathematical equations that relate fire characteristics to wind,
fuel moisture, and topographic conditions for 16 benchmark fuel types.
The system utilizes a moisture content of surface fuels and the moisture
content of the mid and deep duff layers to indicate levels of fire intensity.
The fine fuel moisture code, or FFMC, represents the moisture content of
litter and find cured fuels.
It expresses the ease of ignition and fuel flammability.
FFMC is sensitive to hourly changes in wind, rain,
and temperature, with a time lag of roughly sixteen hours.
The Duff Moisture Code, or DMC, represents the moisture content of loosely
compacted duff that determines resistance to control.
DMC is sensitive to rain, relative humidity,
and temperature, with the time lag of approximately twelve days.
The Drought Code, or DC, represents the deep duff layer that determines resistance
to extinguishment;
it indicates seasonal drought.
The DC is sensitive to rain and temperature, with a time lag of 52 days.
The inter-relationships between the FFMC, DMC, DC, and the wind speed produce
the initial spread index, the build-up index, and the fire weather index.
The Initial Spread Index, or ISI,
represents a numerical rating for fire spread immediately after ignition.
It fluctuates with wind speed and time of day.
The ISI is a combination of wind speed and FFMC.
The Buildup Index, or BUI,
represents total fuel available for combustion.
The Buildup Index is a combination of the Duff Moisture Code and the Drought Code,
and fluctuates little throughout the day.
The Fire Weather Index, or FWI,
represents overall potential for fire intensity and spread.
The FWI is a combination of ISI and BUI.
These codes and indexes are interrelated, so in order to assess fire behavior and
evaluate fire danger, all need to be taken into consideration.
Here is a basic chart to help estimate fire potential and track the progression
during any given fire season.
Just remember that as the numbers increase, so does the fire danger.
Several reference materials are available to you with information about
CFFDRS, including the Alaska Handy Dandy