A proposed method for converting total dust threshold limit values (TLVs) to thoracic or inhalable dust TLVs in the absence of particle size distribution data was described. The first step in the procedure was to determine whether the material of interest could exist as airborne particles and if so to determine whether the particles were likely to be deposited in the lungs or tracheobronchial region. Tentative TLVs were adopted utilizing data on the collection efficiencies of currently used total dust samplers and ideal thoracic and inhalable dust samplers. The tentative TLVs were published and users were encouraged to collect data using as wide a variety of samplers and workplaces as possible and publish their findings. The collected data were used along with any available toxicological and epidemiological data to obtain final TLVS by adjusting the tentative TLVs. The final TLVs for inhalable and thoracic dust were supposed to represent the mass concentrations of the inhalable and thoracic fractions above which an unacceptable risk was expected. The procedure was illustrated by estimating tentative TLVs for inhalable and thoracic dusts utilizing data obtained by a 37 millimeter closed faced filter cassette during wind tunnel tests with polydisperse aerosols. The tentative TLV for inhalable dust was equal to the current TLV for total dust. The tentative thoracic dust TLV was equal to 75% of the total dust TLV. The author concludes that this procedure can be used to estimate TLVs for thoracic and inhalable dusts from TLVs for total dust for airborne particulates when other industrial hygiene or toxicological data are lacking.
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