Respirable crystalline silica dust exposure during concrete finishing (grinding) using hand-held grinders in the construction industry

Studies reporting the findings of exposure to crystalline silica dust during concrete finishing in construction settings are scarce due to the dynamic nature of the activity and the existence of many confounding factors. This study was initiated to explore the issue. A total of 49 personal respirable dust samples were collected during concrete finishing while workers used hand-held grinders. Only 15 (31%) of the grinders were equipped with local exhaust ventilation (LEV) systems. The confounding factors (e.g. wind velocity, wind direction, relative humidity and ambient temperature) were determined. To make the sampling task-specific, air sampling was activated only during actual grinding. Task-specific sampling times during each work shift ranged from 10 to 200 min. The concentration of total respirable particulate ranged from 0.34 to 81 mg/m(3), vith a mean SD of 18.6 +/- 20.4 mg/m(3), and the concentration of crystalline silica in the samples ranged from 0.02 to 7.1 mg/m(3), with a mean SD of 1.16 +/- 1.36 mg/m(3). LEV on the grinders reduced the silica dust level significantly (P < 0.01) compared to grinders without LEV. Increased wind velocity also reduced the silica dust concentration significantly (P < 0.03). Working upwind reduced the exposure to silica dust compared to working downwind, but the difference was not statistically significant. The time-weighted average concentration of silica dust in 69% of the samples exceeded the current recommended threshold limit value of 0.05 mg/m(3), indicating a strong need to devise methods for controlling workers' exposure to crystalline silica dust during concrete finishing activities.