Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB 347-16a, 2013 Oct; :1-32
Background: Workplace exposure to respirable crystalline silica can cause silicosis, a progressive lung disease marked by scarring and thickening of the lung tissue. Quartz is the most common form of crystalline silica. Crystalline silica is found in several construction materials, such as brick, block, mortar and concrete. Construction tasks that cut, break, grind, abrade, or drill those materials have been associated with overexposure to dust containing respirable crystalline silica. Highway construction tasks that can result in respirable crystalline silica exposures include breaking pavement with jackhammers, concrete sawing, milling pavement, clean-up using compressed air, and dowel drilling. Dowel drilling machines are used to drill horizontal holes in concrete pavement so that dowels can be inserted to transfer loads across pavement joints. NIOSH scientists are conducting a study to assess the effectiveness of dust control systems sold by dowel drill manufactures by measuring exposures to workers operating dowel drills with and without dust controls installed. This site visit was part of that study. Assessment: NIOSH staff visited the Archer Western Contractors site at the Hartsfield-Jackson Atlanta International Airport on April 16-20, 2012, and performed industrial hygiene sampling on April 17, 19, and 20, 2012. The sampling measured exposures to respirable dust and crystalline silica among two workers that operated four-gang dowel drills to drill holes in a new concrete runway. The NIOSH scientists who visited the site also monitored the temperature, relative humidity, wind speed and direction, and collected data (e.g., air flow, design) about the dust controls and observed the work process in order to understand the conditions that led to the measured exposures. Results: The quartz content of bulk dust samples collected at this site ranged from 35 to 48 percent by weight, with an arithmetic mean quartz content of 41 percent. Time weighted average respirable dust concentrations at this site ranged from 0.17 to 1.9 mg/m3, with a geometric mean of 0.68 mg/m3. Time weighted average respirable quartz exposures ranged from 0.024 to 0.42 mg/m3, with a geometric mean of 0.13 mg/m3. Conclusions and Recommendations: The geometric mean respirable dust exposure at this site was almost 80% lower when compared to two previous sites visited during this study. In addition to the use of the dust control, the difference may have been due to better maintenance of the dust control system at this site. Despite the lower exposures when compared to two previous sites, the respirable dust exposures of one employee exceeded the OSHA construction industry PEL for respirable dust containing >1% quartz on two days. At this site, the 10-hour TWA quartz exposure of one employee exceeded the NIOSH REL on two days and approached the NIOSH REL on the third day, even though the sampling time was only two hours in duration on that day. Employees should continue to wear half-facepiece air-purifying respirators with n-95 filters for protection against the respirable dust and respirable quartz exposures they encounter while dowel drilling. The respirators should be used as part of a comprehensive respiratory protection program with elements that include training, fit-testing, and medical qualification of the users. Video exposure monitoring highlighted some sources of the workers' exposures. For example, the filters from the dust collection system were cleaned with compressed air. The use of compressed air to clean those filters should be prohibited. In addition to creating a potential source of dust exposure, cleaning the filters with compressed air may also damage the filter media and shorten the service life of the filters. The drill operators also dumped buckets of concrete dust collected by the dust collection system on the ground between the runway slabs. This practice increased the likelihood that the dust became airborne again, which created a potential exposure hazard. Alternative work practices include providing a covered receptacle nearby, or providing extra buckets and the lids to cover them. The covered receptacle or the covered buckets could be collected at the end of the day for disposal (check local regulations) or perhaps returned to the batch plant for recycling.
Region-4; Control-technology; Engineering-controls; Construction; Construction-equipment; Construction-industry; Construction-materials; Construction-workers; Machine-operation; Machine-operators; Equipment-design; Equipment-operators; Respirable-dust; Dusts; Dust-collection; Dust-collectors; Dust-control; Dust-control-equipment; Control-equipment; Control-systems; Concretes; Road-construction; Road-surfacing; Testing-equipment; Silica-dusts; Silicosis; Quartz-dust; Respiratory-system-disorders; Lung-disease; Pulmonary-system-disorders; Lung-disorders; Exposure-assessment; Air-sampling; Air-sampling-equipment; Sampling; Exposure-levels; Exposure-limits; Permissible-limits; Work-practices; Performance-capability; Air-flow; Climatic-conditions; Monitoring-systems; Employee-exposure; Jack-hammers; Drilling; Temperature-measurement; Relative-humidity; Time-weighted-average-exposure; Air-purifying-respirators; Respirators; Filters;
Author Keywords: Silica; concrete; dust; construction; drill; quartz
National Institute for Occupational Safety and Health, Division of Applied Research and Technology, Engineering and Physical Hazards Branch, Mail Stop R-5, 4676 Columbia Parkway, Cincinnati, OH 45226-1998