Prescribed fires are regulated by states and are always subject to strict air-quality standards. Their use must be planned carefully to keep the smoke they produce at acceptable levels. Managers can predict the direction of smoke plumes by relying on meteorological reports and using computer models. Managers avoid smoke-sensitive areas by burning under weather conditions that minimize smoke formation and problems. Occasionally, smoke from a prescribed fire may accumulate in a community, but any impacts are typically light and often last no more than a few hours. Wildfires, however, burn under uncontrolled and unplanned circumstances, making it difficult to manage how much smoke is produced and where it goes. The primary factor in determining the generation of smoke is the amount of vegetation consumed.