Simply put, and ACD is a single stage air sealed incinerator. This is accomplished by providing a very high velocity curtain of air over an earthen fire box (or one with refractory walls). What makes an air curtain effective is a very high volume and high velocity of air distributed evenly across the nozzle length in a laminar flow across the fire box width at a downward angle, trapping incomplete partially burned material, allowing re-circulation back to the core fire with added oxygen and turbulence resulting in higher temperatures (up to 2200 degrees) netting a more complete burn faster and virtually smoke-free. The environmental benefit of a ACD burn results from the higher temperature burning off many pollutants that would otherwise escape into the atmosphere or ground water. The ACD also reduces the chance of fire spread by containment of burning material under a lid of air at high velocity and high volume of air injected are consumed by the fire producing a balance pressure between the pressure under the air curtain and the ambient air pressure above. This results in little or no visible smoke and debris escaping the pit except when loading.