Variability of Exposure and Estimation of Cumulative Exposure in a Manually Operated Coal Mine

This study aims at estimating variability in exposure to respirable dust and assessing whether the a priori grouping by job team is appropriate for an exposure‐response study on respiratory effects among workers in a manually operated coal mine in Tanzania. Furthermore, estimated exposure levels were used to calculate cumulative exposure. Full-shift personal respirable dust samples (n = 204) were collected from 141 randomly chosen workers at underground and surface work sites. The geometric mean exposure for respirable dust varied from 0.07 mg m � 3 for office workers to 1.96 mg m � 3 for the development team. The analogous range of respirable quartz exposure was 0.006‐0.073 mg m � 3 . Variance components were estimated using random effect models. For most job teams the within-worker variance component was considerably higher than the between-worker variance component. For respirable dust the estimated attenuation of the linear exposure‐response relationship was low (5.9%) when grouping by job team. Grouping by job team was considered appropriate for studying the association between current dust exposure and respiratory effects. Based on the estimated worker-specific mean exposure in the job teams, the arithmetic mean cumulative exposure for the 299 workers whoparticipatedintheepidemiologicalpartofthestudywas38.1mg · yrm � 3 forrespirabledust and 2.0 mg · yr m � 3 for quartz.