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    To prevent the unintentional transfer of insects and pathogens during world trade, wood products are often heat sterilized. The general requirement is that the center of the wood configuration be held at 133°F (56°C) for 30 min. However, many factors can affect the time required to reach this temperature. This study explored several of these factors, including thickness of boards or cross-sectional dimension of square timbers, wet-bulb depression, and stacking method (solid or stickered). The heating temperature used was 160°F (71°C). Heating time increased with increasing board thickness or increasing cross-sectional dimension. It also increased as wet-bulb depression increased because of surface cooling when simultaneous drying occurred at significant wet-bulb depressions. Solid piling increased heating time by a factor ranging from 2 to 10 compared with stickered piling, depending on species and size. This study also looked at developing an analytical method to predict heating time as a function of heating variables. Multiple regression was successful as a prediction tool as a function of wood size, wetbulb depression, and initial wood temperature as long as the wet-bulb temperature in the heating chamber was higher than the target center temperature. The multiple regression results were used to create 99% upper confidence levels on estimated heating times.

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    Simpson, William T.; Wang, Xiping; Verrill, Steve. 2003. Heat sterilization time of ponderosa pine and Douglas-fir boards and square timbers. Res. Pap. FPL-RP-607. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 24 p.


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    Heat sterilization, lumber, dry kilns

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