Debris burning is the number one cause of wildfires, closely followed by intentionally set or “arson” fires. The 4 PM Burning Law was adopted during the 1940s to reduce the number of wildfires which occurred each spring, when Virginia has traditionally seen an increased number of fires.
Fires are more likely during late winter and early spring because winds are usually elevated, the relative humidity is lower, and the fuels on the forest floor are extremely dry, having “cured” all winter without the shade of tree leaves. After 4:00 p.m., winds usually calm down and the relative humidity levels rise, both of which reduce the potential for a debris fire or any outdoor open-air fire to escape.