Utilization of western hemlock and western firs for poles and piles Public Deposited
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The steadily increasing costs of raw materials, of the treated products, and of their replacement in service, as well as the steadily shrinking supply of preferred species, prompted a forum at Oregon State University on May 15, 1973 "to encourage the use of western hemlock and western fuss for poles and piles by presenting information on their availability and characteristics and discussing its implications for their utilization." The forum was attended by 27 representatives from wood preserving plants, utilities, and raw material suppliers, and research personnel from western United States and Canada. This survey of relevant information, prepared for the forum, consists of an annotated bibliography of published and unpublished literature, plus an appendix, which contains a bark key, number of trees of pole and piling size by diameter classes, sapwood depth and bark thickness of selected species by diameter classes, and stress values for poles. The index, which lists the information by subject matter, served as the agenda for the forum. The available quantity of pole- and piling-size trees of western hemlock and western firs (Table 1) shows that these nondurable species are an important potential source of supply. Bark-thickness values indicate that peeling residues will be lower with hemlock than with most of the firs (Table 2). These species are permitted for poles in Standard 05.1 1972, American National Standards Institute (Table 3), and for piles in Standard D25-70, American Society for Testing and Materials. No standards exist, however, for their preservative treatment by pressure processes. All have deep sapwood (Table 2), which should make them especially well suited for piles and for distribution poles and the smaller transmission pole sizes in which they are available in greatest quantity. As the bark characteristics do not appear to be sufficiently different to provide a basis for segregating western hemlock and fir logs, and the wood of hemlock is difficult to distinguish from that of the firs without a microscope, standards for poles may have to be revised to include a hem-fir group with the fiber stress value for the firs. Full-length incising appears necessary to insure uniform penetration of preservative in the sapwood of western hemlock and should prove equally desirable for the firs. Deep endpenetration and correspondingly high retentions of preservative could result in excessive treatment of short members.
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