Respirable Crystalline Silica Exposures During Asphalt Pavement Milling at Eleven Highway Construction Sites

摘要

Asphalt pavement milling machines use a rotating cutter drum to remove the deteriorated road surface for recycling. The removal of the road surface has the potential to release respirable crystalline silica, to which workers can be exposed. This paper describes an evaluation of respirable crystalline silica exposures to the operator and ground worker from two different half-lane and larger asphalt pavement milling machines that had ventilation dust controls and water-sprays designed and installed by the manufacturers.Manufacturer A completed milling for eleven days at four highway construction sites in Wisconsin, while Manufacturer B completed milling for ten days at seven highway construction sites in Indiana. To evaluate the dust controls, full-shift personal breathing zone air samples were collected from an operator and ground worker during the course of normal employee work activities of asphalt pavement milling at eleven different sites.Forty-two personal breathing zone air samples were collected over 21 days (sampling on an operator and ground worker each day). All samples were below 50 µg/m³ for respirable crystalline silica, the National Institute for Occupational Safety and Health recommended exposure limit. The geometric mean personal breathing zone air sample was 6.2 µg/m³ for the operator and 6.1 µg/m³ for the ground worker for the Manufacturer A milling machine. The geometric mean personal breathing zone air sample was 4.2 µg/m³ for the operator and 9.0 µg/m³ for the ground worker for the Manufacturer B milling machine. In addition, upper 95% confidence limits for the mean exposure for each occupation were well below 50 µg/m³ for both studies. The silica content in the bulk asphalt material being milled ranged from 7% to 23% silica for roads milled by Manufacturer A and from 5% to 12% silica for roads milled by Manufacturer B.The results indicate that engineering controls consisting of ventilation controls in combination with water-sprays are capable of controlling occupational exposures to respirable crystalline silica generated by asphalt pavement milling machines on highway construction sites.