A TECHNICAL NOTE number 259 UNITED STATES DEPARTMENT OF AGRICULTURE FOREST PRjQBJJLGTS 1 LABORATORY _ UNIV. OF MADISON 5, WISCONSIN FOREST SERVICE Work at the Forest Products Laboratory has shown that fungi in wood are killed by heat most effectively when the moisture content of the wood is above the fiber saturation point. The data in table 1 were obtained for wood infected with Lenzites sepiaria, Lentinus lepideus, and Poria incrassata,_ all prominent decay fungi. The moisture content of the wood was kept above the fiber saturation point while the heat was applied. Table 1. --Recommended times at various temperatures to kill fungi in wood* Wood heal ed in Wood hea ted in air steam or equivalent 90 to 97 percent : 35 to 40 percent relative humidity relative humidity Temperat ure Time T emperature Time Temperature Time °F. Min. °F. Min. °F. Min. 150 60 150 100 160 165 190 60 170 30 170 30 170 50 180 20 180 20 200 10 212 5 ♦The temperature is that of the wood, not that at the surface of the wood. — Chidester, Mae S. Temperatures Necessary to Kill Fungi in Wood. Proc. Amer. Wood- Preservers' Assn. 13:316-324. 1937. In a later series of tests^i that involved 6 fungi and 5 wood species, a similar time-temperature relationship was found. The following is a listing of the fungi used and their source: Fungus* Wood and locality from which obtained Lentinus lepideus Fr. Lenzites sepiaria (Wulf. ) Fr. Poria mcrassata (B. and C.) Burt. Fomes roseus Fr. Lenzites trabea (Pers. ) Fr. Trametes serialis Fr. Jack pine (Pinus banksiana) Canada Eastern hemlock (Tsuga canadensis) Wisconsin Southern yellow pine, Virginia Jack pine (Pinus banksiana) Canada Western redcedar (Thuja plicata) Wisconsin Douglas-fir (Pseudotsuga menziesii) Oregon * The first 3 fungi are the same strains as used in the first studies — Chidester, Mac S. Further Studies on Temperatures Necessary to K:ll Fungi in Wood. Proc. Arm-r. Wood-Preservers' Assn. J5: $19-324. 19 Table Z presents the time-temperature relationships recommended on the basis of the second series of tests. Table 2. --Recommended times at various temper atures to kill fungi in green wood Wood heated in steam or an equivalent Temperature* Time °F. Min. 150 75 170 30 180 ZO ZOO 10 Z1Z 5 ^Internal temperatures, not temperatures at the surface of the wood. The recommended heating periods were based on the time after the wood had reached 150° F. These periods provide a margin of safety in that they are somewhat longer than the studies indicated were necessary for sterilization. The recommendations in table 2 coincide with those in table 1 except that the heating period at 150° F. was increased from 60 to 75 minutes because of the longer time needed to kill Lenzites trabea. Work at the Forest Products Laboratory has shown— that these recommendations are easily met by ordinary commercial treatments of green wood when the preservative temperature is above 150° F. It does not appear practical to sterilize wood at internal temperatures lower than 150° F. The most resistant fungi tested were not lulled alter 12 hours at 140*. Z0 hours at 1> 1 ° , or 24 hours at 122* F. M.i. L< '•■ .1 i) Comments on: Temperatures Necessary to Kill E in Wood. Proc. Amer. Wood Preservers' Assn Z M | UNIVERSITY OF FLORIDA lllllllllllllilll 3 1262 09216 7047