INVESTIGATION OF THE PERFORMANCE OF AGRICULTURAL VEHICLE CAB FILTRATION SYSTEMS

The performance of cab filtration systems in agricultural vehicles has been studied: (1) by measurement of the efficiency of the filters, (2 ) by measurement of air leakage past the filters and (3) by in-cab sam pling of dust and micro-organisms, but not pesticides. Filter efficien cy has been measured in previous work. In the present work, leakage wa s measured on-site, using artificially generated aerosols. In-cab samp ling was carried out with membrane filter samplers. Cab filters made o f cellulose paper or ordinary textile fibres have a low efficiency whe n new. Electrically charged filters and glass-fibre filters can perfor m well, although fibre-shedding from glass-fibre filters and limited l ifetime of electrically charged filters may cause problems. Leakage of air and fine dust varies between 0.5% and 30% depending on design. Gr ain dust concentrations inside cabs during harvesting are usually cons iderably lower than the limit of 10 mg m(-3) but concentrations of mic ro-organisms are often much higher than those in other work environmen ts. No evidence was found of significant leakage of dusty air into the cabs through normal air exit routes. Replacement of an old filter by a new one, or of a low efficiency filter by a higher efficiency filter , frequently caused the in-cab dust concentration to increase, indicat ing clogging or dust dislodgement. A further possibility is that dust may be carried into the cab on the driver's clothing, or that previous ly introduced dust may be dispersed. The results taken as a whole sugg est that the cab/filter system could reasonably achieve a protection f actor of 100, where protection factor is defined as the quotient of th e concentration of dust immediately outside the cab and the concentrat ion inside.