Respirable silica and noise exposures among stone processing workers in northern Thailand

Silica and noise are highly prevalent occupational exposures in the stone processing industry. Monitoring for silica and noise are expensive tasks that may be especially difficult to perform in low-resource settings, but exposure awareness is vital for protecting worker health. This study evaluated personal noise and silica measurements at a stone processing facility in northern Thailand to investigate the differing exposure potentials and risk for overexposure among the varying job categories. Our research team performed repeated personal noise and respirable silica measurements on 46 workers, over three separate workshifts for each of 46 workers. While 36.2% of noise measurements exceeded the recommended exposure limit of 85 dBA, only three silica measurements (2.4%) were above the threshold limit value (TLV) of 25 µg/m³. Self-reported personal protective equipment use was low, with only 27.5% of participants wearing hearing protection in noisy environments during their monitored shift and 29.7% of workers wearing respiratory protection during dusty portions of their shift. We identified a significant positive correlation between measured noise and silica levels (r = 0.54, p < 0.01), with stone loaders having the highest average noise (mean = 89 dBA, standard deviation = 4.9 dBA) and silica (geometric mean = 6.4 µg/m³, geometric standard deviation = 1.8) exposure levels. In a multivariate model, the stone loader job category was a significant predictor of exposure to detectable levels of respirable silica (p < 0.01). These results provide useful guidance regarding the need for noise and silica exposure interventions in order to reduce incidences of workplace disease in the stone processing industry.