Fumigant Usage for Wood Pole Protection
One of the grim realities with any manufactured product, which could also philosophically be extended to life itself, is that things deteriorate from the point at which they are new. The rate at which they deteriorate is governed by the elements to which they are exposed.
One of the largest investments of an electric utility is their pole plant, not only in terms of the cost of the pole, but also the installation, the hardware, the liability and a long list of other things.
For years, various fumigants have been used to extend the life of in-service poles after the original preservative had been depleted. The best available today is universally agreed upon by all. It goes by the name “Chloropicrin”. Unfortunately, it also has another, more recognizable name: “Tear Gas”. It is not used much any more for the simple handling problem, but the old guys that used to use it all have a great story.
The next best thing is also pretty much agreed upon, but it comes in several forms that eventually degrade to the formulation that works. The end product that is agreed upon is known by the acronym “MITC” or methylisothiocyanite.
Currently, there are 3 forms that it comes in and big differences in performance. I will keep it short and sweet here. My source for numerical data in the following table can be found in the 1999 and 2005 Oregon State University Utility Pole Research Cooperatives.
Woodfume (Metham Sodium) is a liquid fumigant that theoretically degrades to 34% MITC.
Basamid (goes by trade names Durafume, Superfume, Ultrafume, ISK Fume) is a powder that recommends mixing of an adjuvant in each application point and theoretically yields 15-45% MITC.
MITC fume is a crystalline solid encapsulated in an aluminum delivery tube that sublimates directly from a solid to a gas. It is 97% pure MITC.
MITC is potent and the amount required to keep a pole from decaying is 20 parts per million (20 micrograms/gram of wood, more accurately). Once it falls below that amount, the wood is susceptible to decay.
The table below shows a simple comparison. A product should activate quickly, move above that 20 ppm number and stay there for an extended period of time.
One should keep in mind two things with this information: 1) The test was in Oregon, which is warmer than we are. The product will perform better for a longer period of time in a colder environment and vice-versa in a warmer environment. 2) The Basamid products recommend mixing of an adjuvant. This was done in a controlled environment with people that took great care for the experiment and had no time constraints. In common practice, there are time constraints and the mixing of the adjuvant and the powder is incomplete at best, yielding inconsistent results at best.
When I decided on this topic, I had my mind made up through my previous experience which product was superior. I will have to admit that I was surprised at the poor results of MITC fume in the later years. In my opinion, it is still the product of choice, even with it being more expensive, but there is some merit with the Basamid products. The biggest problem is one of mixing the adjuvant properly in the field. I have never seen it done consistently to date. The only merit with Woodfume is the low cost. It will protect a pole for 2 years maximum and will sometimes attracts rodents. Factor in the borings that you have to make for application and the case could be made for doing more damage to the pole than helping it.