Engineering Controls Database

Dowel Drilling Machine – Silica Exposure

Problem:	Dowel drilling machines (or dowel drills) are used to drill horizontal holes in concrete pavement. Dowel drilling is a task performed during new concrete airport runway and highway construction (e.g., when a lane is added) or during full-depth repair of concrete pavement to provide load transfer across transverse pavement joints. Steel dowels transfer loads between adjacent concrete pavement slabs [Park et al. 2008]. Dust that may contain crystalline silica is generated during the use of dowel drilling machines (see Figure 1) [Linch 2002, Valiante et al. 2004]. [img=1]
What this means to you:	Breathing dust that contains crystalline silica can lead to silicosis, a deadly lung disease. No effective treatment exists for silicosis, but it can be prevented by controlling workers’ exposures to dust containing crystalline silica. Exposure to crystalline silica has also been linked to lung cancer, kidney disease, reduced lung function, and other disorders [NIOSH 2002]. The National Institute for Occupational Safety and Health (NIOSH) initiated a research project to evaluate the effectiveness of current dust controls for dowel drilling machines, work with manufacturers to improve dust controls if necessary, and promote the use of tools with dust controls.
Description of control:	Typical dowel drilling machines have one or more drills held parallel in a frame that aligns the drills and controls wandering [FHWA 2006]. The dowel drilling machine may be self propelled or boom mounted, and may ride on the slab or on the subbase [FHWA 2006]. After drilling to a typical depth of 23 cm (9 inches (in)) the anchoring material is placed, and the dowel is installed. The diameter of the hole is determined by the dowel diameter and whether cement-based grout or an epoxy compound is used to anchor the dowels [FHWA 2006]. The use of engineering control technology such as dust control systems would be the preferred solution and adhere to the hierarchy of controls. There are currently only two manufacturers of dowel drills in the United States (Minnich and E-Z Drill) and they both offer optional dust control systems for their new drills that can be retrofitted to older model drills. Those dust control systems, like most local exhaust ventilation (LEV) systems, consist of hoods, ducts, air cleaners, and air movers. The hoods surround the drill steel and bit at the work surface. They collect the concrete dust, which is produced in an air stream directed toward the hood. Flexible ducts convey the dust and air to the air cleaner. The air cleaner contains a cartridge filter to remove the contaminant from the airstream. The air mover must produce the desired air flow despite losses due to friction, fittings, and hood entry [ACGIH® 2010]. Minnich uses eductors to move the air in their system. E-Z Drill uses pneumatic dust collectors on smaller drill rigs and a pneumatic fan on larger gang drills. Both manufacturers also sell water spray systems to suppress drilling dust. E-Z Drill uses a water spray that wets the surface of the concrete. Minnich injects water into the hole through the hollow drill steel and an orifice in the bit. Two approaches were used by NIOSH to evaluate the effectiveness of the dust controls. The first was to measure respirable dust emissions from dowel drilling machines in a controlled setting, isolated from the effects of wind, weather, and other sources of particulate, assessing the effectiveness of the controls in reducing emissions. Emissions with and without the use of controls were compared. The second approach assessed personal respirable dust and respirable crystalline silica exposures of workers operating dowel drilling machines with dust controls in place in a real-world setting to determine the ability of the dust controls to limit exposures.
Engineering and Physical Hazard Report Numbers:	347-12A; 347-13A; 347-14A; 347-15A;
References:	ACGIH® [2010]. Industrial ventilation – a manual of recommended practice. 27th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists. FHWA [2006]. Full-depth repairs. Washington, DC: U.S. Department of Transportation, Federal Highway Administration, Office of Pavement Technology. [http://www.fhwa.dot.gov/PAVEMENT/concrete/full5.cfm] Linch, K. D. [2002]. Respirable concrete dust—silicosis hazard in the construction industry. Applied Occupational and Environmental Hygiene 17:209-221. [http://dx.doi.org/10.1080/104732202753438298]. NIOSH [2002]. NIOSH Hazard Review: Health effects of occupational exposure to respirable crystalline sil¬ica. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Pre¬vention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2002–129. [http://www.cdc.gov/niosh/docs/2002-129/]. NIOSH [2011a]. In-depth survey report: control technology for dowel-pin drilling in concrete pavement at Minnich Manufacturing, Mansfield, OH. By Echt A, Mead K, Feng HA, Farwick D Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB 347–12a [http://www.cdc.gov/niosh/surveyreports/pdfs/347-12a.pdf]. NIOSH [2011b]. In-depth survey report: control technology for dowel-pin drilling in concrete pavement at EZ Drill, Perry, OK. By Echt A, Mead K, Feng HA, Farwick D Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB 347–13a [http://www.cdc.gov/niosh/surveyreports/pdfs/347-13a.pdf]. NIOSH [2011c]. In-depth survey report: control technology for dowel-pin drilling in concrete at the Columbus Municipal Airport, Columbus, IN. By Echt A, Mead K, Kovein R Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB 347–14a [http://www.cdc.gov/niosh/surveyreports/pdfs/347-14a.pdf]. NIOSH [2011d]. In-depth survey report: control technology for dowel drilling in concrete at the Springfield-Branson National Airport, Springfield, MO. By Echt A, Hirst DVL, Kovein R Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB 347–15a [http://www.cdc.gov/niosh/surveyreports/pdfs/347-15A.pdf]. NIOSH [2012a]. In-depth survey report: control technology for dowel drilling in concrete at the Hartsfield-Jackson Atlanta International Airport, Atlanta, GA. By Echt A, Kovein R, Lambright J Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB 347–16a [http://www.cdc.gov/niosh/surveyreports/pdfs/347-16a.pdf]. NIOSH [2013]. In-depth survey report: control technology for dowel drilling in concrete at Laborers International Union of North America Local 172, Folsom, NJ. By Echt A, Mead K, Kovein R Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB 347–17a [http://www.cdc.gov/niosh/surveyreports/pdfs/347-17a.pdf]. Park C-G, Jang C-I, Lee S-W, Won J-P [2008]. Microstructural investigation of long-term degradation mechanisms in GFRP dowel bars for jointed concrete pavement. J Appl Polym Sci 108:3128–3137. [http://onlinelibrary.wiley.com/doi/10.1002/app.27946/abstract]. Valiante, D. J., Schill, D. P., Rosenman, K. D., & Socie, E. [2004]. Highway repair: A new silicosis threat. Am J Public Health 94(5):876–880 [http://ajph.aphapublications.org/doi/abs/10.2105/AJPH.94.5.876].
NAICS Codes:	333120
Keywords:	crystalline silica crystalline silica dowel drilling machines dowel drilling machines dowel drills dowel drills
How well does this control work?	The dust control evaluated in two reports [NIOSH 2011a, 2011b] included a close-capture hood surrounding each drilling tool at the work surface, a length of corrugated flexible hose connected to each hood, and dust collectors at the back of the dowel drill unit. Compared with the use of no dust control during dowel drilling in concrete, the dust-control system significantly (p<0.0001) reduced geometric mean respirable dust mass concentrations by 89% to 96% when measured with filter samples. Arithmetic mean respirable dust concentrations measured on filters were significantly (p<0.0001) reduced 88% to 96% by the use of the dust control system. NIOSH also performed field studies to evaluate dowel drills used in airport runway construction [NIOSH 2011c, 2011d, 2012]. Three site visits were conducted, including two sites where dust controls were used and one with no dust control in use. The time weighted average respirable dust results from the two sites where controls were used were compared with data from sites where no control was in place, including Linch’s [2002] data. On average, the geometric mean respirable dust concentration was five times lower at sites where dust controls were used. While the difference was not significant (p=0.12), this was likely due to the small sample size and resultant loss of experimental power, not due to an absence of effect. The probability of a difference of the means, 0.88, approaches 90 percent significance. Finally, to ascertain if the difference in the extent of reductions seen in the lab versus those seen in the field was due to the design of the control or due to its use and maintenance or operator training, NIOSH [2013] performed a site visit to a training center with a new drill transported from the factory. A representative of one of the drill manufacturers instructed apprentice trainers in the use and maintenance of the drill prior to air sampling. The dust control performed well under the test conditions.