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 fungal 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 research 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 available
commercially 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 1970's as
WoodFume®. Metam-sodium is a liquid
formulation containing 33% metam-sodium that chemically decomposes in the pole
to release mitc. However, the breakdown of metam-sodium is not
complete, with a metam-sodium-to-mitc
conversion efficacy of only 18%.
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%-mitc and was commercially introduced by Osmose in the late 1980's
as MITC-FUME®. At 97% 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%-mitc
available in the market.
Powder/granular fumigants: The third, and most recently commercialized mitc-based fumigant, is dazomet. Dazomet was introduced in the late 1990's 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%
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 due in part to 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 as 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.
Since 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. Furthermore, 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 extremely important when
attempting to control an active decay infestation.
Oregon State University - Utility Pole
Research Cooperative
Oregon State University (OSU) has worked on fumigant development
since the 1970's, 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 which can be
found here: http://www.cof.orst.edu/coops/utilpole/PDFgallery.htm.
You can learn more about Osmose fumigants here.
About the Author
Doug Herdman is the Director of Science and Manufacturing at Osmose. He holds a BS in Wood Science and a MS in
Environmental and Resource Engineering both from SUNY-ESF at Syracuse. He has over 20 years of experience formulating
and testing remedial wood preservative technologies. In his current role, he oversees the design,
development, and commercial production of Osmose's industry-leading wood
preservative technologies. Doug serves
on the AWPA (American Wood Protection Association) P1 Subcommittee as the
General Chairperson and is an advisor to the Executive Committee.
