Heat sterilization times of five hardwood species

Abstract

Heat sterilization of lumber, timbers, and pallets is currently used to kill insects, thus preventing their transfer between countries in international trade. An important factor in this treatment is the time required for the center of any wood configuration to reach the temperature necessary to kill the insect. This study explored the effect of size (1-, 1.5-, and 2.0-in.-thick by 6-in.-wide boards, and 3- by 3-, 4- by 4-, and 6- by 6-in. timbers), hardwood species (red maple, sugar maple, red oak, basswood, and aspen), and two wet-bulb depressions (nominal 2°F and 8–10°) at a nominal heating temperature of 160°F. Two analytical methods were examined for their ability to calculate estimated heating times. Heating times varied from about 15 min for 1- by 6-in. boards to 300 min for 6- by 6-in. timbers. Heating time was about 15% longer at the larger of the two wet-bulb depressions. Some species differences were significantly different statistically but were not different enough in practical terms to warrant heating separately. We found that the wet-bulb temperature could be used successfully in an analytical model as the heating temperature when evaporation of water cooled the surface below the nominal heating temperature.

Citation

Simpson, William T.; Wang, Xiping; Forsman, John W.; Erickson, John R. 2005. Heat sterilization times of five hardwood species. Res. Pap. FPL-RP-626. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 10 p.