During a regional alert when high pollution potential exists, all prescribed burning should be postponed. Nighttime burning should be done with additional care because a temperature inversion may trap the smoke near the ground. In particular, smoke mixing with existing fog will drastically reduce visibility. Cool air drainage at night will carry smoke downslope, causing visibility problems in lowlands and valleys. On the Coastal Plain, nighttime air drainage often follows waterways.
Conditions can be especially hazardous near bridge crossings because of the higher humidity there.
Of course, the earlier in the day a fire is completed, the less likely it is to cause nighttime smoke problems. More complete mopup following daytime burning and nighttime burning only under very stringent prescriptions can minimize the occurrence of these problems. Your local State forestry office can help with planning nighttime burns. Effects on Human Health and Welfare Occasional brief exposure of the general public to low concentrations of drift smoke is more a temporary inconvenience than a health problem. High smoke concentrations can, however, be a very serious matter, particularly near homes of people with respiratory illnesses or near health-care facilities.