Ann Suter, Statistician, WFCS
The figure above shows the relationship between
fire retardant, drop height, and length of line at different
coverage levels. Two drops were made with gum-thickened retardant
at heights of 112 and 315 feet, respectively. Also, two drops
were made with water at heights of 144 and 201 feet. The numbers
above the bars indicate the coverage level attained for a length
of retardant line.
A 203-foot increase in drop height for gum-thickened
retardant produced less of a change in line length at coverage
levels 2 and 4 than a 57-foot increase for water. The difference
between gum-thickened retardant dropped at 315 feet and water
dropped at 144 feet is remarkable. Gum-thickened retardant produces
longer line lengths at almost all the coverage levels.
The Forest Service tests
aerial delivery systems to evaluate drop characteristics and
ground patterns of fire fighting chemicals. Data from early
drop tests suggest an increase in the elasticity of fire retardant
from adding a gum-thickener results in larger droplets within
the retardant cloud.Larger droplets
-
have less exposed
surface area relative to volume,
-
and therefore less
evaporation;are less impacted by wind, thermal drafts,
and drop height.
The result is more retardant
reaches the ground.
E-mail: cjohnson12@fs.fed.us