the coastal plains areas, features such as swamps, rivers, roads, etc. are a
major factor in fire control, but slope is not. In managing smoke, however, even slight slopes become a very
important factor. The majority of
highway accidents have occurred because of down-drainage smoke at night
or smoke spreading into open areas.
sun striking the earth’s surface heats it during the day.
The warmer air close to the surface warms and expands as it rises. The
air along the surface
of a slope,
being warmer and lighter, tends to rise up-slope, resulting in up-slope winds.
At night, the reverse is true. Such
movement of air, which is very noticeable in mountainous areas, is so slow in
flat (coastal plains) areas, it is not noticeable.
Also, winds during the day will generally overcome this phenomena in coastal
and piedmont areas. At
night however, the general winds usually die down and the local down-slope and
down-drainage winds occur, even though very slowly.
This local wind flowing down-slope at the surface will carry residual
smoke down-drainage into lower areas. The
smoke is not diffused as it is during the day.
Instead, as drainages come together, it concentrates and becomes thicker.
can be smelled at very low concentrations (a few parts per million).
Somewhat higher concentrations can be seen, and as it increases, can reduce
visibility. At night, this
reduction is also abrupt--the same as with fog.
It does not “feather out” at the edge like it does during the day.
Consequently, the visibility can change from clear to almost zero in a
Even a slight reduction of visibility on interstates is a real problem. Although most people will slow down when smoke is encountered, some people (knowing the interstate is wide and straight) will either continue through the smoke at the same rate of speed or not slow down as much as other drivers in front of them.
This problem is compounded by the fact that the visibility of
red taillights is drastically reduced in both smoke and fog.
Taillights on older vehicles, being smaller and generally weaker, may
not be visible past a few feet. Drivers
rarely turn on their flashers--even though they have slowed to less
than 30 mph on
an interstate. Some people don’t
remember to turn them on even when they stop.
Smoke on interstates and major highways can result in drastic consequences including fatalities and damages in the millions of dollars.Down-drainage Smoke is a Killer!
Why will smoke flow down-slope and down drainage at night?
Be prepared for a lawsuit if an accident occurs close to your burn – Document!
What to do after an incident occurs.