"Total" and respirable dust exposures in the U.S. carbon black manufacturing industry

This article describes an industrywide exposure assessment study of "total" and respirable carbon black dust exposures among U.S. carbon black manufacturing workers conducted between 1993 and 1995. In addition to updating a 1979-1980 industrywide "total" dust study conducted among all major U.S. carbon black producers, this research was the first comprehensive evaluation of respirable dust exposures in the U.S. industry. A total of 2060 samples were collected (n = 1,004 "total," n = 1,056 respirable). The distributions of both dust fractions were lognormal with an overall "total" dust mean concentration, represented as the maximum variance unbiased estimator of 0.59 mg/m3 (range = 0.01-13.25 mg/m3), and an overall respirable dust mean concentration of 0.15 mg/m3 (range = 0.01-2.62 mg/m3). The fraction of "total" dust exposures greater than the current Occupational Safety and Health Administration permissible exposure limit of 3.5 mg/m3 was less than 3%. Material handling jobs experienced the highest "total" and respirable dust exposures, a finding consistent with the 1979-1980 study. The highest mean exposure for an individual job title was observed for product baggers/packers/sackers at 2.30 mg/m3 for "total" dust and 0.48 mg/m3 as respirable dust. Overall, mean "total" dust exposures had decreased significantly (up to 70%) for the majority of job classifications since the 1979-80 study. To evaluate the relationship between "total" and respirable dust fractions, 680 matched pairs of respirable and "total" samples were analyzed with a resulting mean ratio of 0.37 (respirable fraction to "total" dust). A log-transformed regression equation was obtained that provides a predictive relationship between "total" and respirable carbon black dust concentrations that may be applied to estimate the respirable fraction of historical "total" dust data collected under similar environmental and manufacturing conditions.