The efficacy of local exhaust ventilation for controlling dust exposures during concrete surface grinding

This study assessed the effectiveness of a commercially available local exhaust ventilation (LEV) system for controlling respirable dust and crystalline silica exposures during concrete grinding activities. Surface grinding was conducted at six commercial building construction sites in Seattle, WA, by cement masons. Time-integrated filter samples and direct reading respirable dust concentrations were collected using a cyclone in line with a direct reading respirable dust monitor. Personal exposure levels were determined with and without LEV, one sample directly after the other. A total of 28 paired samples were collected in which three different dust collection shroud configurations were tested. Data obtained with a direct reading respirable dust monitor were adjusted to remove non-work task-associated dust exposures and was sub-sequently used to calculate the exposure reduction achieved. The application of LEV resulted in a reduction in the overall geometric mean respirable dust exposure from 4.5 to 0.14 mg/m3, a mean exposure reduction of 92%. Despite the effective control of dust generated during surface grinding, 22 and 26 % of the samples collected while LEV was being used were greater than the 8 h time-weighted average permissible exposure limit (Occupational Safety and Health Admin-istration) and threshold limit value (American Congress of Governmental Industrial Hygie-nists) for respirable crystalline silica, respectively