Conserving energy by environmentally acceptable practices in maintaining and procuring transmission poles for long service ; August 1992

Abstract

Evaluation of previously established field trials of remedial internal treatments demonstrates the continued performance of chioropicrin, Vorlex, and methylisothiocyanate (MITC). While the degree of protection afforded by these treatments has declined with time, residual fungitoxic levels remain in many tests. Field trials of gelatin encapsulated MITC indicate that gelatin had no negative effect on fumigant performance even when no water was added at the time of treatment. Closed tube bioassays, chemical analyses, and culturing of Douglas-fir and southern pine poles treated with glass encapsulated METC (MITC-Fume) indicate that this chemical is outperforming metham sodium 3 years after application. While the glass vials lost chemical very slowly, the slow release rate did not appear to adversely affect MITC performance. Trials to evaluate the performance of fused borate rods were sampled after 1 or 2 years of exposure. Chemical analysis of cores removed from the test poles revealed that none of the treatments contained boron at levels which would be considered adequate for arresting or preventing colonization by wood decay fungi. Interestingly, boron levels in poles exposed in Hilo, Hawaii were highest above the treatment hole, suggesting that some upward diffusion of this chemical is possible. The low boron levels in these poles are reason for concern, since a number of utilities are considering the using this formulation for remedial treatment at the groundline. Evaluations of new solid fumigants are progressing. Trials with Basamid indicate that the addition of copper compounds improved the rate of decomposition to produce MITC. Simultaneous addition of copper sulfate and Basamid may be useful for accelerating the decomposition of this compound, making it practical for control of internal decay fungi. Trials have been established to evaluate the performance of gelled and pelletized metham sodium and a sodium fluoride/boron rod. These trials will be evaluated in future reports. A third field trial to evaluate the performance of a copper naphthenate/boron paste for internal treatment of Douglas-fir poles is currently be evaluated to determine chemical levels 3 years after treatment. The performance of gelled metham sodium was further evaluated under laboratory conditions to better understand the performance of this chemical. Gelled metham sodium provided improved fungal control in comparison with liquid metham sodium and appeared to produce increased MITC levels under a variety of test conditions. The improved performance of this formulation may reflect the ability of the gell to retain moisture for longer periods of time than the liquid metham sodium formulation. Further studies of this formulation are underway. Laboratory studies were also performed to evaluate the effects of various additives on the performance of Basamid. Once again, the addition of copper compounds enhanced the production of MITC. A number of other compounds shifted decomposition to the production of carbon disulfide and carbonyl sulfide, two less fungitoxic compounds. Further studies are underway to identify non-sulfur products which may provide some protection against wood decay fungi. Evaluations of the effects of artificial voids on performance of fumigants in Douglas-fir poles indicate that voids had little or no effect on fumigant distribution. As a result, fumigant treatment of solid wood around voids represents a viable strategy for improving pole service life. Evaluation of timbers treated with metham sodium indicate that detectable levels of MITC were present one year after treatment. These timbers will be evaluated in subsequent years to determine the protective period provided by fumigants in sawn material. We continue development of a fumigant movement model using data previously developed on MITC. This year, we evaluated a previously developed system, ANSYS. Results of preliminary trials are similar to data previously developed on MITC-Fume treated poles and indicate that modeling MITC movement should be possible. Further trials are underway to confirm and expand this model. The effect of wood moisture content, temperature and wood species on metham sodium decomposition was investigated under laboratory conditions. The efficiency of dcomposition to MITC varied widely, but was most affected by temperature and wood moisture content. The results suggests that there is considerable potential for improving decomposition efficiency to enhance performance of this fumigant. Further studies to characterize the relationship between chemical content of the wood species and decomposition are underway. Field trials to identify safer treatments for preventing decay of cedar sapwood and protecting field drilled bolt holes are continuing. Diffusible treatments continue to provide excellent protection for field drilled bolt holes. A study to develop estimates of the extent of decay above the groundline in Douglas-fir poles in the Pacific Northwest is underway. The data from this study will be used to develop estimates of the potential for damage and provide some insight into the extent of this problem. Studies to develop guidelines for sterilization of Douglas-fir poles following air-seasoning are continuing. Evaluations of internal temperature development during kiln-drying were completed this year and indicate that internal temperatures during typical pole drying schedules were more than adequate for acheiving sterilization. Further evaluations of the data are underway to develop reliable heating curves for this process. Evaluations of groundline preservative systems have been established at Corvallis, OR and Merced, CA. The results indicate that all of the formulations are moving well through the wood in a manner similar to that found with pentachlorophenol-based systems. Chemical levels in some treatments; however, are beginning to decline 30 months after treatment. Studies are now underway to establish thresholds for combinations of the various formulations. Copper naphthenate treated western redcedar stakelets continue to perform well in fungus cellar trials. Stakes weathered prior to treatment are degrading slightly faster, while freshly sawn stakelets continue to perform well. Field trials have also been established to evaluate the performance of copper naphthenate treated Douglas-fir utility poles in California and Oregon. The chemical levels and fungal colonization will be monitored in these poles to provide a guide to performance of this chemical in western wood species.