|
|
| |
| |
|
PSA NFDRS Component Glossary |
|
| |
| Energy Release
Component (ERC) is a number
related to the available energy (BTU)
per unit area (square foot) within
the flaming front at the head of a
fire. Daily variations in ERC are
due to changes in moisture content
of the various fuels present, both
live and dead. Since this number represents
the potential "heat release"
per unit area in the flaming zone,
it can provide guidance to several
important fire activities. It may
also be considered a composite fuel
moisture value as it reflects the
contribution that all live and dead
fuels have to potential fire intensity.
The ERC is a cumulative or "build-up"
type of index. As live fuels cure
and dead fuels dry, the ERC values
get higher thus providing a good reflection
of drought conditions. The scale is
open-ended or unlimited and, as with
other NFDRS components, is relative.
Conditions producing an ERC value
of 24 represent a potential heat release
twice that of conditions resulting
in an ERC value of 12. |
| |
| 1000-Hour
Fuel Moisture (1000-hr FM)
represents the modeled moisture content
in dead fuels in the 3 to 8 inch diameter
class and the layer of the forest
floor about four inches below the
surface. The 1000-hr FM value is based
on a running 7-day computed average
using length of day, daily temperature
and relative humidity extremes (maximum
and minimum values) and the 24-hour
precipitation duration values. Values
can range from 1 to 40 percent. |
| |
| 100-Hour
Fuel Moisture (100-hr FM)
represents the modeled moisture content
of dead fuels in the 1 to 3 inch diameter
class. It can also be used as a very
rough estimate of the average moisture
content of the forest floor from three-fourths
inch to four inches below the surface.
The 100-hr FM value is computed using
length of day, maximum and minimum
temperature and relative humidity,
and precipitation duration in the
previous 24 hours. Values can range
from 1 to 50 percent. |
| |
Burning
Index is a number related
to the contribution of fire behavior
to the effort of containing a fire.
The BI (difficulty of control) is
derived from a combination of Spread
Component (how fast it will spread)
and Energy Release Component (how
much energy will be produced). In
this way, it is related to flame
length, which, in the Fire Behavior
Prediction System, is based on rate
of spread and heat per unit area.
However, because of differences
in the calculations for BI and flame
length, they are not the same. The
BI is an index that rates fire danger
related to potential flame length
over a fire danger rating area.
The fire behavior prediction system
produces flame length predictions
for a specific location.
The BI is expressed
as a numeric value related to potential
flame length in feet multiplied
by 10. The scale is open-ended which
allows the range of numbers to adequately
define fire problems, even during
low to moderate fire danger. |
| |
| Fuel Model
G is used for dense conifer
stands where there is a heavy accumulation
of litter and downed woody material.
Such stands are typically overmature
and may also be suffering insect,
disease, wind, or ice damage -- natural
events that create a very heavy buildup
of dead material on the forest floor.
The duff and litter are deep and much
of the woody material is more than
3 inches in diameter. The undergrowth
is variable, but shrubs are usually
restricted to openings. |
|
|
