Residual Smoke (Smoldering Fire)
same volume of fuel consumed with a smoldering fire will produce roughly five
(5) times the amount of smoke as a flaming fire. Also, the heat produced during the “flaming phase” lifts
most of the smoke off the ground.
more intense a fire, the less smoke is produced for the amount of fuel consumed.
This is because the combustion process is more effective and more fuel is
consumed during the flaming phase than during the residual phase. Theoretically,
if the combustion process could be 100% effective, there would be no
smoke problem--only carbon dioxide and water vapor would be produced.
However, this is impossible, especially in open burning.
Control could also become a problem if the fire is too intense. Overstory could also be damaged or killed.
containing waxes or rosin also produce more smoke because of incomplete
combustion, even though they burn more intensely. Examples are Palmetto and Gallberry.
Action to Take:
following factors will result in more fuel being consumed during the “flaming
phase” thus reducing the amount of smoke produced.
Less Volume of Fuel
Waxes or Rosins
Stumps or Snags
Windrows and Large “Dirty” Piles
windrows results in most of the fuel being consumed during the smoldering phase
that produces more residual smoke. Burning
time is extended, large amounts of smoke are produced, and little heat is
generated to lift the smoke off the ground.
Much of the smoke is produced during the night when atmospheric
conditions are stable. It takes
days for the burning process to be completed.
The reasons are:
Large volume of fuel
fuel moisture content
percentage of fuel exposed to sunlight
air circulation due to dirt and compaction
Windrows are the most polluting of all fuels used in the South.
Large amounts of smoldering smoke is produced that takes days to burn out. Much of the smoke is also produced at night.
Site quality is reduced. Top soil is removed and no litter is left leaving areas of soil being completely exposed to the sun and rain. The top layer is baked out and soil pores become clogged by the rain.
Action to Take:
Do NOT Burn Windrows--leave scattered or use piles
Start Early in the Day & Stop Early
During Unstable Conditions
Use Small, Dry Piles
During High Mixing Height
Pile When Dry
With High Transport Winds
Shake Out Dirt
With Low to Moderate Surface Winds
during the night results in more smoldering fire due to these factors:
atmospheric conditions (no lift)
heating of fuel from the sun
or no wind
winds (local effect)
fine fuel moisture
smoke produced will not lift because of atmospheric stability.
This is because there is no heat from the sun which causes vertical
movement in the atmosphere. With no
heating, little or no wind, and relatively high humidity, most of the combustion
process will occur during the smoldering (residual) phase.
Even during the flaming phase, less heat is generated and consequently
smoke is lifted very little.
little or no wind and no vertical movement in the atmosphere, local conditions
take over. Smoke produced will stay
near the ground and downslope winds will carry it downslope and down-drainage!
Most smoke-related accidents have been the result of down-drainage flow
of smoke at night.
If you must burn at night, wait unto a cold front moves through area and the wind is forecasted to blow all night. Use in young plantations or other grass-type fuels where loading is low.
Action to Take:
Burn during daytime hours whenever possible
At night, only burn grass-type fuel with low volume.
Use Backing Fire (Most of fuel consumed during flaming phase)
Burn after a strong cold front
Burn when relative humidity is under 80%
Burn when there is no inversion
Burn when winds are forecast for all night
extra cautious when burning as much as 300 acres, or areas with a heavy loading
of fuel (both aerial and ground ignition).
Residual smoke, which tends to concentrate in the same drainage as it
flows down-slope at night, can lead to heavy concentrations of smoke in low
areas. Burning blocks of 500 or
more acres will almost always result in a smoke problem, even in isolated rural
areas. Large burns take longer, result in burning later in
the afternoon, and
produce more residual smoke than smaller burns.
After dark, the smoke plume will start settling back to the ground. On large burns, even
with small amounts of residual smoke, it will all flow into the same
drainage--increasing the concentration of smoke.
into smaller blocks
especially cautious of the forecast.
out the blocks to be burned in one day
when atmospheric conditions are favorable
down-drainage Smoke-Sensitive Areas special attention.
for other nearby burns
Be sure smoke from different blocks does not come together within the impact distance determined in the screening system
Good burning days, especially for understory burns, are infrequent. Aerial ignition is a good way to burn a large number of acres on “good” dispersion days--and in the middle of the day when atmospheric conditions favor lift and dispersion of smoke. When used properly, aerial ignition allows more burning with better smoke dispersion than other methods. It is important to remember, however, that the atmosphere can quickly be overloaded when large blocks are ignited at one time! Many smoke-sensitive areas downwind have been adversely affected by too much smoke being produced at one time as the result of helicopter burns. This can occur even during the middle of the day.
If area is fired too rapidly, it could develop into "mass ignition" where a large area burn very intensly and rapid due to the numerous sources of heat at one time. The result is on-site damage and possibly of escape. Another problem is the cost of having the unit on standby waiting for the "right" weather conditions. This fact could push you to burn on marginal days.
especially cautious of Smoke Sensitive Areas; give them plenty of room.
not burn when either fog or relative humidity over 80% is predicted for that
night and any residual smoke is anticipated.
not burn when inversions are forecasted for that night!
for other burns close by.
not burn one large block. Burn
smaller blocks scattered in different drainages.
only one part of the block with just a few lines, and go on to the next one.
Come back to the first block after starting all of them.
Use a 4-wheeler equipped with an air-pressure firing torch rather than a
helicopter, especially when smoke-sensitive areas are close.
ignition as soon as inversion has burned off.
ignition of new fuel early in the day, in time for residual smoke to die
down before dark.
Burn only when mixing height is at least 3,000 feet! And ... never depend just on the forecast ... observe!