Respirable Crystalline Silica Exposure among Concrete Finishing Workers at Apartment Complex Construction Sites

The objective of this study was to evaluate the level of exposure to respirable crystalline silica (RCS) among concrete finishers and to identify the size distribution of particles from concrete finishing work at apartment complex construction sites. Active personal air sampling (n = 129) was conducted at eight sites using filters with aluminum cyclones, and local air sampling for the size distribution of the particles (n = 6) was conducted using a Mylar substrate with cascade impactors. Crystalline silica was analyzed by Fourier-transform infrared spectroscopy (FT-IR). The collected personal samples were sorted by the type of task (concrete chipping, grinding, or plastering) for four kinds of working places (exterior walls, interior walls of apartment units, staircases, and underground parking lots). The geometric mean (GM) of the RCS concentration was highest, although varying according to the type of structure, for concrete grinding (2.06 mg m(-3)), followed by chipping (0.12 mg m(-3)) and plastering (0.003 mg m(-3)). The maximum RCS concentration was measured in the staircases (4.18 mg m(-3)), followed by the interior walls of apartment units (2.76 mg m(-3)), underground parking lots (1.30 mg m(-3)), and exterior walls (0.89 mg m(-3)). The mass fraction of inhalable, thoracic, and respirable crystalline silica was respectively 73.9%, 40.2%, and 17.9% in chipping and 76.0%, 46.3%, and 19.7% in grinding. Concrete finishing workers at apartment complex construction sites are exposed to unacceptably high concentrations of RCS. To protect workers' health, dust-minimizing construction methods as well as high-efficiency respirators paired with local exhaust ventilation systems or wet methods must be employed. Further efforts to reduce the total working time and to use full-faced air-purifying respirators are required.