Resumen de Laboratory Measurements of the Performance of Pesticide Filters for Agricultural Vehicle Cabs against Sprays and Vapours
A. Thorpe, M.J. Bagley, R.C. Brown
Pesticide filters for use in agricultural vehicle cabs contain a vapour filter element, sometimes with a particulate filter element upstream. The former normally comprises a granular carbon filter and the latter a pleated paper or electrostatic fibrous filter. Pesticides are normally applied to crops in the form of sprays but a certain amount of vapour is always present in any spray of a volatile compound. The efficiency of a number of fibrous filters used in tractor cabs has been measured against droplets of spray designed to resemble pesticide spray to which the vehicle might be exposed during crop or orchard spraying. The evaporation of pesticide vapour from captured droplets and its subsequent capture by activated carbon filters has also been investigated. In the first experiments, carried out in a medium-sized test tunnel, a tracer of strontium chloride in dilute solution was used, along with a nozzle of the sort used in practice. Samples were collected before and after the filters using small eight-stage cascade impactors. The performance of the filters with respect to the sprays followed the same pattern as that previously observed with solid particles of the same size. Pleated paper filters were of low efficiency, whereas specimens of both glass fibre filters and electrically charged filters performed well. The performance of a scaled down particulate/vapour filter was measured using real pesticides. A finite amount of evaporation from droplets on the particulate filter was observed and was related, albeit imperfectly, to the vapour pressure of the pesticide. Evaporation did not increase consistently with temperature, possibly because of decomposition of the pesticide. The efficiency of commercially available carbon filters for capture of vapour was found to be about 90%, but it is not certain whether the penetration of vapour was due to failure of the filter to capture it or to leakage.
