DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Summary 

Construction workers may be 

exposed to hazardous dust containing respirable crystalline silica when using dowel drilling machines to drill horizontal holes 

in concrete pavement. The National Institute for Occupational Safety and Health (NIOSH) 

found that exposures were reduced using tool-mounted local 

exhaust ventilation (LEV) and 

good work practices.

Reducing Hazardous Dust Exposure 

When Dowel Drilling in Concrete

Description of

Exposure

Breathing dust that contains respirable 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 respirable crystalline silica has been linked to lung 

cancer, kidney disease, reduced lung 

function, and other disorders [NIOSH 

2002]. Crystalline silica is found in several construction materials, such as 

brick, block, mortar and concrete. The 

NIOSH recommended exposure limit (REL) for respirable crystalline silica is 50 micrograms per cubic meter 

(μg/m3

) as a time weighted average for up to a 10 hour workday during a 40 hour work week. Respirable 

dust is the fraction of the aerosol that 

is small enough to reach the deeper, 

gas-exchange region of the lung.

Many highway construction tasks produce dusts that can contain respirable 

crystalline silica. These tasks include 

breaking pavement with jackhammers, 

concrete sawing, milling pavement, 

clean-up using compressed air, and dowel drilling [Valiante et al. 2004]. Dowel 

drilling machines (also known as gang 

drills or dowel-pin 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 fulldepth repair of concrete runways and 

highways to provide load transfer across 

transverse pavement joints. Steel dowels 

are partially inserted into the holes and 

fixed into place. Once the adjacent new 

slab is poured and cured, the dowels 

distribute loads between adjacent concrete pavement slabs [Park et al. 2008]. 

Typical dowel drilling machines have 

one or more drills held parallel in a 

frame that aligns the drills and holds 

them steadily during drilling. The dowel drilling machine may be self-propelled or boom mounted, and may 

ride on the slab or on the subbase. After drilling to a typical depth of 23 

cm (9 inches), the anchoring material is placed, and the dowel is partially inserted into the hole. 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].

Dust is generated during the use of 

dowel drilling machines and this dust 

typically contains crystalline silica 

(Figure 1). NIOSH researchers documented respirable crystalline silica exposures for workers operating dowel 

drilling machines of up to 26 times the 

NIOSH REL during full-depth pavement repair and up to eight times the 

NIOSH REL during new runway construction [Linch 2002, NIOSH 2011c].

NIOSH Project

NIOSH initiated a research project to 

evaluate the effectiveness of dust controls for dowel drilling machines, to 

work with manufacturers to improve 

dust controls if necessary, and to promote the use of tools with dust controls [NIOSH 2012]. The results of this 
project demonstrate that LEV dust control systems on dowel 

drilling machines can be very effective. The efficacy of water 

sprays alone or in combination with LEV controls was not 

assessed in the NIOSH study.

In the first phase of the project, a pilot study was conducted that measured respirable dust emissions from a five-drill 

dowel drilling machine that was operated in a tent, isolated from the effects of wind, weather, and other particulates. 

The machine was started remotely and stopped drilling automatically at a preset depth. The pilot study showed that 

the LEV dust control system reduced dust concentrations by 

89% [NIOSH 2008]. Two subsequent studies [NIOSH 2011a, 

b] were conducted under similar conditions, one with a fourdrill machine and one with a five-drill machine. When the 

results of those two studies were combined and analyzed, 

they showed that emissions without the dust control were 

14 times greater than when the control was in use. In other words, the dust control reduced respirable dust emissions 

by 93%.

In the next phase of the project, NIOSH researchers performed field studies to evaluate dowel drills used in airport 

runway construction [NIOSH 2011c, 2011d, 2012].Three 

sites were visited, including two sites where dust controls 

were used (two five-drill machines at the first site and two 

four-drill machines at the second) and one with no dust control in use (two four-drill machines). On average, the respirable dust concentration at airport runway sites where dust 

controls were used was one-fifth the level measured at airport runway and highway construction sites where no dust 

controls were used. In other words, the dust control reduced 

respirable dust emissions by 80%. However, even with the 

LEV system in use, TWA respirable crystalline silica exposures exceeded the NIOSH REL by an average of 3 times and 

up to 8 times [NIOSH 2012].

NIOSH researchers [NIOSH 2013] also investigated whether the greater reductions of dust seen in the first phase of the 

project compared with those in the second phase were due 

to the design of the control, its use and maintenance, or operator training. A study was conducted at a training center 

using a new one-drill machine transported from the factory 

(Figure 2). A representative of a drill manufacturer instructed apprentice trainers in the use and maintenance of the drill 

prior to air sampling. The drill-mounted dust control performed well under the conditions of the test, controlling silica exposures to levels below the NIOSH REL when the drill 

was properly used and maintained by trained operators.

Figure 1. Laborer operating a slab-riding, four-drill dowel 

drilling machine without dust controls.

Figure 2. Trainer operating a slab-riding, single-drill dowel drilling machine with LEV system at training center.

Controls

NIOSH identified two manufacturers of dowel drills in the 

United States. Both manufacturers offer optional dust control systems on their new equipment. Dust controls can also 

be retrofitted to older model drills. Those dust control systems, like most LEV systems, consist of hoods, ducts, air 

cleaners, and air movers. The hoods surround the steel and 

bit at the work surface (Figure 3). They collect the concrete 

dust 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]. Both manufacturers also sell water spray systems to suppress drilling dust. Water spray systems were not evaluated during the NIOSH project.

Recommendations

NIOSH has evaluated LEV dust control measures to reduce 

worker exposure to hazardous dust during dowel drilling operations and recommends their use [NIOSH 2008, NIOSH 

Photo by NIOSH

Photo by NIOSH
2011a, 2011b, 2011c, NIOSH 2012, NIOSH 2013]. The recommendations below should reduce exposures associated 

with dowel drilling.

LEV System

These recommendations are based on good industrial ventilation engineering design practices. NIOSH researchers did 

not encounter any dowel drill dust controls that incorporated all of these features.

 Use smooth ducts and maintain duct transport velocity at 

3,500 to 4,000 feet per minute [ACGIH 2010].

 Provide duct clean-out points.

 Install pressure gauges across dust collection filters so the 

drill operator knows when to clean or change the filter.

Work Practices 

 Train workers to use and maintain the dust collector in 

accordance with manufacturer specifications.

 Avoid work practices that place the worker in a dust cloud, 

such as marking pavement while the drill is running. Ensure 

that workers nearby are also protected from dust exposures.

 Provide a covered receptacle near the drill to discourage 

drill operators from dumping the collected concrete dust 

on the ground, where it can become airborne.

 Do not clean the cartridge filter manually with compressed air. In addition to creating a hazardous dust cloud, 

compressed air can damage the filter.

 Review the trouble-shooting guide provided by the manufacturer to recognize signs that the dust collector is not 

working properly.

 Dust that collects in the exhaust hoses should be removed 

manually, for example, by raising and lowering the drill array. Compressed air should not be used to clean the hoses.

Site Set-Up

 Develop a site-specific safety and health plan. The plan 

should include guidance for recognizing when silica dust 

may be generated and describe strategies to control or 

eliminate dust. Include engineering controls, personal 

protective equipment, and work practices.

 During dowel drilling operations, use LEV or wet control 

systems to control dust. When purchasing dowel drilling 

equipment, opt for dust controls. Always use the dust control system and keep it well maintained. Do not use equipment if the dust control system is not working properly.

 Establish a documented maintenance program for the 

dust control systems.

 Provide training to drillers in the use of controls and work 

procedures.

 During dowel drilling, perform air monitoring of respirable crystalline silica exposures to make sure engineering 

controls are working and to determine whether workers 

need respiratory protection.

Respirators

 The dust controls identified in this report should 

greatly reduce worker exposure to hazardous dust; however, NIOSH-certified respirators may still be necessary 

to reduce exposure to crystalline silica below the NIOSH 

REL of 50 μg/m3.

 With properly functioning dust controls in place, it may 

be possible to use less restrictive respirators, such as those 

with an assigned protection factor of 10, since the amount 

of hazardous dust has been decreased.

 Exposure monitoring is necessary to determine what type 

of respirator is needed.

 Employers should follow the Occupational Safety and 

Health Administration (OSHA) Respiratory Protection Standard (29 CFR 1910.134) (www.osha.gov/SLTC/

etools/respiratory/index.html).

Personal Hygiene, Protective Clothing, and 

Work Practices

 Wash hands and face before eating, drinking, or smoking.

 Do not eat, drink, or use tobacco products in the work 

area where construction activities are being performed.

 Change into disposable or washable work clothes at the 

worksite. If possible, shower and change into clean clothes 

before leaving the worksite to avoid contaminating cars, 

Figure 3. Diagram of slab-riding, single-drill dowel drilling machine showing the major components of the LEV 

system.

Photo by NIOSH
homes, and other work areas. If it is not possible to shower or change into clean clothes, use a vacuum with a highefficiency filter to remove dust from clothes. An effective 

method to remove dust from clothing involves a booth under negative pressure that uses an air spray manifold to 

blow dust from clothing [Pollock et al. 2006].

 Do not use a compressed air hose to remove dust from 

clothing.

 Park cars where they will not be contaminated with silica dust.

 Remove dust from equipment using a water hose rather 

than compressed air.

This document was prepared by Alan Echt, NIOSH Division 

of Applied Research and Technology, and John J. Whalen, 

formerly with NIOSH. Kimberly Clough-Thomas (NIOSH 

Health Effects Laboratory Division) prepared the illustration. 

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. Available on-line at 

http://www.fhwa.dot.gov/PAVEMENT/concrete/full5.cfm. 

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17:209–221.

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Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) 

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drilling at Minnich Manufacturing, Mansfield, OH. By Echt 

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Department of Health and Human Services, Centers for 

Disease Control and Prevention, National Institute for Occupational Safety and Health, Report No. EPHB 334-11a.

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Feng HA, Farwick D. Cincinnati, OH: U.S. Department of 

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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.

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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.

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 

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for dowel drilling in concrete at the Hartsfield-Jackson Atlanta International Airport, Atlanta, GA. By Echt A, Kovein 

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and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and 

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A, Mead K, Kovein R. Cincinnati, OH: U.S. Department of 

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Park C-G, Jang C-I, Lee S-W, Won J-P [2008]. Microstructural investigation of long-term degradation mechanisms 

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Suggested Citation

NIOSH [2015]. Reducing hazardous dust exposure when dowel drilling in concrete. By Echt A, Whalen J. Cincinnati, OH: U.S. 

Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational 

Safety and Health. DHHS (NIOSH) Publication No. 2015-200.
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Reducing Hazardous Dust Exposure When Dowel 

Drilling in Concrete

DHHS (NIOSH) Publication No. 2015-200

SAFER • HEALTH • PEOPLETM August 2015