In the preparation of the fire plan, managers carefully study the site to minimize the risk of fire escaping from the burn unit. One way managers decrease the risk is by constructing a barrier, or firebreak or fire line, around the prescribed fire site. Natural firebreaks, such as roads, ditches, water or other physical features devoid of natural fuel are the best barriers. Frequently, however, a firebreak must be built ahead of time to remove materials that would fuel a wildfire. Mowing and wetting down the area with fire hoses are methods used to prevent fire from burning outside the prescribed area.
On the day of the prescribed fire, the fire crew considers all environmental elements, the most important being relative humidity, temperature, moisture in the vegetation and wind speed and direction. Wind determines where the fire will be ignited and in which direction it will burn; the fire plan specifies which wind directions are acceptable. If conditions are not appropriate, the burn is delayed.