Forest fires can be divided into two broad classes-wildfires and prescribed fires. Wildfires, whether caused by nature (lightning, etc.) or by the accidental or malicious acts of man, are not planned by forest managers and do not occur under controlled conditions. They can be relatively tame, covering only a few hectares and burning only understory litter, or they can be catastrophic firestorms like the recent one in Australia that covered over 400,000 hectares. Some wildfires cause severe damage to life and property as well as timber, wildlife, soil, water and air resources. Effective fire control and prevention programs have reduced the annual U.S. wildfire loss from 18 million hectares in the early 1930's to less than 1.6 million hectares in the middle 1970's. This reduction represents a significant savings in human and natural resources and one can speculate on the obvious benefits to air quality.