The 4 p.m. Law is a ban (or restriction) on open air burning before 4 o'clock in the afternoon if your fire is within 300 feet of the woods or dry grass which can carry the fire to the woods. You are allowed to burn between 4 p.m and midnight as long as you take proper care and precaution and attend your fire at all times.
The law goes into effect on February 15th each year and runs through April 30th.
The 4 p.m. Law was adopted during the 1940's to reduce the number of wildfires which occurred each spring. During this time of the year, Virginia traditionally has an increased number of fires. During the winter months, winds are usually elevated, the relative humidity is lower and the fuels on the forest floor are extremely dry, having "cured" without having the tree leaves to shade them.
After 4 p.m., winds usually calm down and the relative humidity levels are on the increase, both of which reduce the potential for a debris fire or any outdoor open air fire to escape your control.
Campfires are ALSO considered an open fire.