Preliminary modelling of methylisothiocyanate movement through Douglas fir transmission poles
A R Zahora, P E Humphrey, J J Morrell
Methylisothiocyanate is a volatile solid that is the active ingredient of several registered and experimental wood fumigants. Information on the sorption and diffusion of this chemical in Douglas-fir heartwood and sapwood was used to develop a two-dimensional model of fumigant movement within a single horizontal cross-section of a transmission pole. The model indicated that dry wood (14% MC) strongly sorbed MIT, which resulted in lower rates of MIT movement. Conversely, it was predicted that wetter wood (22 or 40% MC) held MIT less strongly and had a more rapid rate of chemical movement. In addition, predictions suggest that the presence of an oil-treated peripheral shell had a strong influence on loss of fumigant from the surface of the pole, but had little effect on concentration which developed in the heartwood zone. The results indicate that MIT movement can be effectively modeled. Further studies are underway to account for longitudinal movement of MIT in the model and to simulate extended time periods.