Mass, number and surface area concentrations of alpha-quartz exposures of refractory material manufacturing workers

This study set out to assess the respirable mass, surface area, and number concentrations of the alpha-quartz content particles (C(r-m), C(r-s) and C(r-n)) to which workers were exposed in six different exposure groups, the raw material handling (n=10), crushing (n=12), mixing (n=12), forming (n=10), furnace (n=10), and packaging (n=10), in a refractory material manufacturing plant. For C(r-m), the exposure values in sequence were found as: mixing (68.1 microg/m3)>packaging (55.9 microg/m3)>raw material handling (53.3 microg/m3)>furnace (31.0 microg/m3)>crushing (29.8 microg/m3)>forming (22.4 microg/m3). We also found that ~21.2-68.2% of the above Cr-m exceeded the current TLV-TWA for the alpha-quartz content (50 microg/m3) suggesting a need for initiating control strategies immediately. We further conducted particle size-segregating samplings in four workplaces: crushing (n=3), mixing (n=3), forming (n=3), and furnace (n=3). We found that all resultant particle size distributions shared a quite similar geometric standard deviation (sigma(g); =2.24-2.92), but the process area, associated with higher mechanical energy (i.e., crushing process), contained finer alpha-quartz content particles (mass median aerodynamic diameter; MMAD=3.22 microm) than those areas associated with lower mechanical energy (i.e., mixing, forming, and furnace; MMAD=6.17, 5.95, and 8.92 microm, respectively). These results gave a ratio of C(r-m) in the above four exposure groups (i.e., crushing: mixing: forming: furnace=1.00: 2.30: 0.753: 1.04) which was quite different from those of C(r-s) (1.00: 1.74: 0.654: 0.530) and C(r-n) (1.00: 1.27: 0.572: 0.202). Our results clearly indicate the importance of measuring particle size distributions for assessing workers' free silica exposures.