By Doug Herdman
How Wood Fumigants Work
Fumigants are generally applied at or near the groundline area of a pole, where conditions for decay are optimal, by drilling a series of steeply angled holes. After the fumigant is applied, holes are sealed with tight fitting plugs. Once plugged, the fumigant is securely contained within the pole. When applied to the pole, the fumigant begins to volatilize and moves throughout the wood as a gas. Fumigants help control existing decay and prevent recolonization of decay fungi by sterilizing the wood, including difficult-to-treat heartwood. The effectiveness of a fumigant is measured by how far the preservative agent travels from the point of application at levels sufficient to protect the pole from fun-gal attack.
History of Wood Fumigants
Since the use of wood utility poles began in the late 1800’s, controlling decay has been a colossal challenge for pole owners. Pioneering re-search conducted in the early 1970’s at Oregon State University (OSU) in a cooperative effort with the Bonneville Power Administration led to the commercialization of agricultural fumigants for utility pole applications. As part of its ongoing fumigant research program, scientists at OSU have conducted extensive laboratory and field studies demonstrating the efficacy of methylisothiocyanate, or mitc, based pole fumigants. The development of these mitc-based fumigants opened the door to an extended service life for wood poles that was previously unattainable.
Wood Fumigant Forms
The mitc-based wood pole fumigants are commercially available in three basic forms: liquid, powder/granular and solid-melt. Each form has its own attributes with regard to application, performance and safety.
• Liquid fumigants: Metam-sodium was the earliest of the mitc-based fumigants and was commercially introduced by Osmose in the late 1970s as WoodFume. Metam-sodium is a liquid formulation containing 33 percent metam-sodium that chemically decomposes in the pole to release mitc. The breakdown of metam-sodium is not complete, however, with a metam-sodium-to-mitc conversion efficacy of only 18 percent. Metam-sodium is commercially available as L-Fume, SMDC-Fume, and WoodFume. The liquid fumigants are applied to the pole through predrilled application holes by directly pouring from the container. While liquid fumigants have favorable handling characteristics, there are concerns over splashing during application, accidental release into the environment, and potential leaking from large seasoning checks in the pole.
• Solid-melt fumigants: The second fumigant is 97 percent mitc and was commercially introduced by Osmose in the late 1980s as MITC-FUME. At 97 percent mitc, it delivers the highest concentration of active ingredient to the pole, and since it doesn’t have to decompose to produce mitc, it provides quick control of decay. MITC-FUME is prepackaged in sealed aluminum tubes, making it the easiest and safest fumigant to apply. There are currently no other forms of 97 percent mitc available.
• Powder/granular fumigants: The third, and most recently commercialized mitc-based fumigant, is dazomet. Dazomet was introduced in the late 1990s by the PoleCare Division of CSI under the tradename ULTRAFUME. Dazomet is a solid powder fumigant that decomposes within a utility pole in the presence of water to release mitc. Like liquid metam-sodium, the conversion efficacy of dazomet-to-mitc is fairly inefficient at only 45 percent under ideal conditions. Dazomet is currently available as DuraFume II, G-Fume, Super-Fume and ULTRAFUME. As a means to accelerate the decomposition to mitc, the EPA product labels for the dazomet fumigants recommend the addition of a copper solution at the time of fumigant application.
In general, powder fumigants provide a greater level of protection than liquid fumigants partly because of the higher conversion efficiency of dazomet. Powder fumigants are typically applied by directly pouring from the container into predrilled application holes. When compared to liquid fumigants, powder fumigants present a slightly lower exposure risk for both the applicator and the environment because they have a reduced potential for splashing, accidental release and leaking from seasoning checks. While the risk of exposure and release are more favorable than liquid fumigants, there are still concerns over the potential for “dusting”—the release of tiny particles into the air during application—and wind-blown exposure if the product is not properly applied and proper PPE is not used. In addition, the direct-pour method can result in variable dosing from hole to hole and it is difficult to effectively apply the copper accelerant to application holes that are already filled with solid fumigant.
Advancement in Fumigant Technology
For the past 20 plus years, fumigant technology has remained essentially unchanged and wood pole owners have been left to weigh the positive and negative attributes of the liquid, powder and solid-melt forms of wood pole fumigants. However, a new form of fumigant—a solid-body dazomet-based fumigant—will be commercially available in 2017.
Fittingly named EZ-FUME, this new fumigant has a stick-like design that makes application safe, clean and easy. EZ-FUME performs best in conjunction with a copper accelerant, and the compact design of the body allows room for three times as much accelerant to be used—when compared to powder/granular fumigants. The profile of the EZ-FUME stick also allows the liquid accelerant to freely flow to the bottom of the application holes and completely submerge the fumigant, providing for vastly improved interaction between the copper accelerant and dazomet.
Because EZ-FUME is manufactured into a solid stick using proprietary techniques, concerns over splashing, accidental release into the environment, and dusting or wind-blown exposure are essentially eliminated. In addition, the pole owner is guaranteed an accurate dosing for each application.
Don’t Be Fooled
Be careful not to confuse diffusible rod treatments with fumigants. Diffusible rods are another type of remedial treatment system with a different set of performance characteristics. Diffusible rods are made with water-diffusible active ingredients that require a relatively high moisture content to perform. First, the active ingredients must be dissolved, and then they eventually diffuse several inches away from the point of application. Fumigants, on the other hand, volatilize and are capable of moving several feet away from the point of application, which is important when attempting to control an active decay infestation.
Oregon State University - Utility Pole Research Cooperative
OSU has worked on fumigant development since the 1970s, studying all commercially available fumigants—and some that are not commercially available—to determine product efficacy. The Utility Pole Research Cooperative was established in 1980 to aid in the development of new fumigants. Over the years, the focus of the cooperative has expanded to address a variety of products and practices that improve the service life of utility poles. The results of all OSU Cooperative studies are published in their annual reports.
About the author: Doug Herdman is the Director of Science and Manufacturing at Osmose. He holds a BS in Wood Science and an MS in Environmental and Resource Engineering both from SUNY-ESF at Syracuse, New York. He has more than 20 years of experience formulating and testing remedial wood preservative technologies. In Herdman’s current role, he oversees the design, development and commercial production of Osmose’s wood preservative technologies. He serves on the American Wood Protection Association P1 Subcommittee as the general chairperson and is an advisor to the executive committee.