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Conserving energy by environmentally acceptable practices in maintaining and procuring transmission poles for long service ; September 1995 Public Deposited

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  • Previously established field trials of MTTC-Fume continue to show that this chemical remains in Douglas-fir and southern pine poles at fungitoxic levels 5 years after treatment. In general, increasing dosages resulted in higher chemical levels in the poles. All of the MITC-Fume treatments resulted in higher residual M1TC levels than comparable metham sodium treatments. Field trials with solid basaniid with and without copper sulfate continue to show the promise of this chemical. Basamid treated poles continue to contain MITC at levels which exceed those for comparable metham sodium treatments. These results, which are currently being confirmed in poles in service, indicate that this formulation can deliver fiingitoxic MITC levels to wood in service, without the risk of spills associated with metham sodium. We have completed trials with gelled and pelletized metham sodium formulations. Both of these formulations offered improved safety during application. Initial laboratory trials also suggested that the gelled formulation was more effective than comparable liquid metham sodium. Field trials, however, indicate that the formulations provided protection comparable to the liquid formulation in poles over the test period. The gelled formulation still offers the advantage of reduced risks of spills during application. Trials are also continuing with various solid, water diffusible treatments for arresting internal decay. Trials of fused borate rods continue to show that these treatments require more moisture for effective movement in Douglas-fir poles. Field trials have also been established with borate rods with glycol as an additive to determine if glycols can accelerate diffusion in drier wood. The poles in these trials have also been sensored to monitor internal moisture changes over time in order to better correlate boron diffusion with wood moisture content. Trials underway with a boronlfluoride rod indicate that the boron is diffusing well from these rods, while the fluoride is moving somewhat slower. Neither chemical has approached a fiungal threshold one year after treatment, but the combination of chemicals may lead to more effective fungal control. Trials with pelletized metham sodium/basamid mixtures suggests that using ratios of these two chemicals can produce an initial rapid burst ofMITC release followed by a slower MITC release with time. This combination allows for rapid control of existing fungal infestations followed by long term protection against reinvasion. These laboratory trials will be further confirmed with field trials. The trials to evaluate the effects of voids on fumigant movement initially suggested that voids have little influence on subsequent fumigant levels on either side of the void. Sampling 8 years after treatment, however, indicates that chioropicrin levels were generally higher in poles without voids. We plan further trials of actual field poles containing voids to confirm these effects. Trials to identify treatments for protecting the sapwood of western redcedar poles as well as wood exposed in field drilled bolt holes are continuing. Trials in western redcedar sapwood have identified a number of chemicals which can be remedially applied to protect this wood against fungal attack. At present, however, commercial pole spraying has largely ceased making further field trials difficult. Field trials to identify treatments for protecting untreated wood exposed during drilling for various pole attachments continue to show that diffusible boron and fluoride compounds provide excellent long term protection against flingal attack. The protective effects of one diffusible treatment, Boracol, however, has begun to decline. Further sampling will be undertaken to identify the long term effectiveness of the remaining treatments. Trials to identify enhanced patterns for through boring of Douglas-fir poles are complete. The results indicate that patterns as widely spaced as 400 mm apart longitudinally still produce a nearly completely treated pole i n the through bored zone. Pentachlorophenol levels in the through bored zone were generally above the threshold for ftrngal growth. Prior sampling of Douglas-fir poles in service suggest that even poles with small skips in the through bored zone contained no evidence of internal decay. These results suggest that the through boring pattern can be extended without adversely risking pole service life. A reduced through boring pattern would decrease treatment costs while minimizing impacts on pole strength. Trials to evaluate the application of boron to freshly peeled Douglas-fir poles as a means of preventing fungal colonization using a thermal process suggest that thermal treatment failed to produce a boron loading sufilcient to permit subsequent diffusion across the pole section after a 3 month diffusion period. Evaluations of various external groundline preservative formulations continue to indicate that replacement formulations based upon copper naphthenate, boron or fluoride perform comparably to earlier formulations employing pentachlorophenol and creosote. Pentachlorophenol levels in some treatments have fallen below the threshold for fungal growth, while those in all of the replacement treatments remain above a U protective level. These results suggest that the newer groundline preservative systems should provide a reasonable level of protection against external decay. Laboratory trials to better understand the levels of combinations of chemicals required for protection in the groundline zone are continuing. Fungal cellar evaluations of copper naphthenate treated western redcedar continue to show excellent performance at levels specified in the American Wood Preservers' Association Standards. Performance is generally better for wood which was freshly sawn prior to treatment, while wood cuts from weathered poles in service has provided slightly lower levels of protection. The weather wood apparently has higher permeability, making it more likely to lose chemical in soil contact. Further evaluations are planned.
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