Distribution of Pentachlorophenol in Pressure and Non-Pressure Treated Douglas-Fir Crossarms

A study was made to determine the relative value of pressure and non-pressure methods of treating Douglas-fir crossarms with pentachlorophenol particularly with regard to the relative retentions of preservative attained in specific portions of the arms. The pressure-treated crossarms studied consisted of six crossarms of Douglas-fir heartwood 8 feet long treated to an average retention of 6.03 lb./cu. ft. The six non-pressure treated crossarms of Douglas-fir heartwood 8 feet long were treated to an average retention of approximately 6 lb./cu. ft. Non-pressure-treated arms were found to have relatively lower pentachlorophenol retentions adjacent to the pin and bolt holes than pressure-treated arms. They had higher retentions in the incised surfaces and retentions similar to pressure-treated arms in the ends. In the least accessible portions of the arms, that is, the centers of cross-sections farthest from pin or bolt holes, the non-pressure-treated arm had lower retention than the pressure-treated arms. Nevertheless, preservative penetrated these areas in the non-pressure-treated arms and relatively good retentions were obtained. The most significant difference found between the two types of treatments was the variation in pentachlorophenol retentions found between similar sections of the individual arms. The pentachlorophenol retentions found in similar sections of the non-pressure-treated arms, for example, varied twice as much as the retentions of similar sections in arms treated by pressure processes.

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