Most of the gas generated during heating of the heat-transfer oil does not come into contact the waste material and can be discharged directly to the atmosphere without emission controls. The remainder of the flue gas maintains the thermal screw purge gas exit temperature above 300 degrees F. This ensures that volatilized organics and moisture do not condense. In addition, the recycled flue gas has a low oxygen content (less than 2% by volume) which minimizes oxidation of the organics and reduces the explosion hazard. If pretreatment analytical data indicates a high organic content (greater than 4 percent), use of a thermal screw is recommended. After the treated soil exits the thermal screw, water is sprayed on the soil for cooling and dust control. Thermal screws are available with soil treatment capacities ranging from 3-15 tons per hour.