FIRE EFFECTS GUIDE - National Wildfire Coordinating Group

document the duration of long-term combustion to the exact minute, it is important
to note whether smoldering combustion lasts for only a few minutes, or a few
hours, or several days.
d. Flame length. Flame length is measured along the slant of the flame. The
accuracy of estimation of flame length can be increased by installing reference
points that provide scale. Steel posts with 1-foot sections alternately painted red
and white or metal flags attached every 3 feet (the choice depends on the
expected scale of the flames) set in the burn area work very well (Rothermel and
Deeming 1980). These markers can be the same as those used to measure rate
of fire spread.
(1) Observations. Flame length data are usually obtained from visual
observations of average flame length at set intervals. Flame length is usually
recorded at the same time as rate of spread observations are made.
(2) Photography. Flame length can be documented with cameras and time and
location of observation of each exposure recorded. Accuracy is enhanced by use
of infrared film.
(3) Video camera. Not only are video cameras an excellent way of documenting
fire behavior, the passive image analyzer mentioned above (McMahon et al.
1987) allows a very accurate measurement of flame length. After a grid of known
size is established on the first frame, the tape is advanced until a representative
flame is seen on the screen. The image is frozen on the screen, and the flame is
outlined on the screen with a cursor. Computer software then calculates flame
length.
e. Burn pattern. A map of the burned area can be made at both a gross and
detailed scale. For general monitoring purposes, a map of the burned area can
show areas where the tree or shrub canopy was removed, areas where the fire
was an underburn, and areas the fire did not burn at all. Information on burn
pattern can be obtained by a walk through the burned area, by long transects, or
with photography. A low elevation aerial photo, or an oblique photo taken from a
high vantage point such as a hill or a tree, can be measured with a dot grid to
determine burn pattern. For large wildfires, satellite imagery can be used to obtain
information on the pattern of burned and unburned areas, and where the fire was
a surface fire or a crown fire. When choosing imagery for analysis, it must be
remembered that up to about 2 weeks may pass before scorch damage to
overstory tree foliage is apparent.
f. Burn severity/Depth of burn. The pattern of burn severity on the surface of
the ground can be quite complex, because it varies with the distribution of prefire
fuel loading and arrangement, thickness of litter and duff layers, and moisture
content of surface and ground fuels. While mapping the pattern of burn in the
surface fuels and vegetation for an entire burned area may be too large a task,