| Abstract: | The rate of gas interchange between the atmosphere within a freight container and the external air has an important influence on the effectiveness of in-container fumigation. When a container is exposed to the wind or is in motion, the rate of gas interchange may be much greater than that under static conditions. The effect of motion or wind on gas interchange was studied by observing gas loss from freight containers, both empty and loaded with rice, while stationary and while being transported by rail. The gas interchange rate was determined by measuring the rate of loss from the containers of either a combination of a fumigant, methyl bromide, and a relatively inert tracer gas, carbon monoxide, or of carbon monoxide alone. In loaded containers the difference between the loss rate constants of methyl bromide and carbon monoxide (0.29.0.03d?1) was within the range expected for the reaction of methyl bromide with rice. After allowing for gas loss caused by changes in temperature and pressure, the component of the interchange rate constant attributable to air motion was found to be proportional to gas-tightness as measured by a steady-state pressure test, and also to the relative air speed over the container. Under conditions of varying wind and train speed, the fraction of the initial concentration of gas remaining was found to be an exponential function of wind run past the container. When wind effects were not important, it was found to be an exponential function of distance travelled. |
