For night burns, backing fires with surface windspeed greater than 4 mph and relative humidity under 80 percent should be prescribed. If it appears that stumps, snags, or logs may cause a residual smoke problem, take steps to keep them from burning. If they do ignite, extinguish them. Daytime value of the Dispersion Index between 41 and 60 is adequate for small fires and low levels of burning activity. As either size of individual fires or level of burning activity increases, the Dispersion Index value should also increase.
Many variables affect the behavior and resulting smoke from a prescribed burn.
The above system works best in fiat terrain and was not designed for use in mountainous country. If your prescribed fire complies with all conditions in these five steps, you should be able to safely burn without causing a smoke problem. If you have any marginal answers, areas that are especially sensitive to smoke, heavy fuel loadings or wet fuels, use the prediction system mentioned in the Southern Forestry Smoke Management Guidebook. You must make the final judgment.