QUANTIFICATION OF HISTORICAL DUST EXPOSURES IN THE DIATOMACEOUS-EARTHINDUSTRY

Quantitative estimates of dust exposure in a diatomaceous earth (DE) m ining and milling operation have been derived based on air sampling re cords for the period 1948-1988. A total of 6395 records was included i n the analysis. Conversion of results obtained by particle counting, e xpressed as millions of particles per cubic feet (mppcf) or gravimetri cally from a filter cassette and expressed as mg m(-3) total, were con verted to mg m(-3) respirable dust using a conversion factor derived f rom data obtained during the same periods al the plant. Conversion fac tors were calculated as the average difference of means on the log sca le in order to provide stable and consistent conversions and as a rati o of arithmetic means so that the results could be compared with simil ar studies. After converting the available data to mg m(-3) respirable dust, geometric mean (geometric standard deviation) concentrations we re 0.37 (2.43) during the 1950s and 0.17 (2.35) during later periods. Exposures were estimated using two linear models, one estimating the c hanges in concentration over time, and the other providing job-specifi c mean exposures during the more recent period. Extrapolation of the e stimates to periods prior to the availability of any data was done usi ng a subjectively-determined scaling factor. The average estimated res pirable dust concentrations for 135 jobs were 3.55 (+/-1.25), 1.37 (+/ -0.48), 0.47 (+/-0.16) and 0.29 (+/-0.10) mg m(-3) prior to 1949, 1949 -1953, 1954-1973 and 1974-1988, respectively. Despite the limitations of the available data, the estimation procedures used are expected to provide reasonable quantitative estimates of silica-containing dust ex posure for subsequent exposure-response analyses. (C) 1997 British Occ upational Hygiene Society. Published by Elsevier Science Ltd.