Special Cautions

Residual Smoke (Smoldering Fire)

The 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.

The 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.

Fuels 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:

The following factors will result in more fuel being consumed during the “flaming phase” thus reducing the amount of smoke produced.

Windrows and Large “Dirty” Piles

Burning 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:

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:

Night-time Burning

Burning during the night results in more smoldering fire due to these factors:

The 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.

With 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:

Large Burns

Be 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.

Action to Take:

Helicopter Burns  

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.

Action to Take:


Caution:  Smoke flows down-drainage at night!