CONTROL OF SILICA DUST IN CONSTRUCTION

Vehicle-Mounted Drilling Rigs for

Rock and Concrete

Using drilling rigs mounted on trucks, crawlers, or other vehicles to drill into rock

or concrete can generate respirable crystalline silica dust. When inhaled, the small

particles of silica can irreversibly damage the lungs. This fact sheet describes dust 

controls that can be used to minimize the amount of airborne dust when using 

vehicle-mounted drilling rigs for rock and concrete as listed in Table 1 of the 

Respirable Crystalline Silica Standard for Construction, 29 CFR 1926.1153.

Engineering Control Method: Dust collection systems with water sprays at the discharge point OR

Operator isolation in an enclosed cab with water on drill bit

Dust Collection Systems/Wet Methods

Dust-collecting equipment for vehicle-mounted drills 

includes a movable duct attached to a close capture 

hood or shroud around the drill bit, and a flexible 

rubber skirt that encloses the drill hole opening and 

captures cuttings that come through the hole.

Dusty air is pulled from inside the shroud through a 

flexible duct to primary and secondary filter media. 

The primary filter or dust separator often includes 

a self-cleaning back-pulse feature that dumps the 

collected particles to the ground.

Secondary release of particles to the air is minimized 

by a low-flow water spray at the discharge point. 

Equipment without these controls can be retrofitted 

by the manufacturer or a mechanical shop.

Illustration courtesy of NIOSH

Water mist

Diagram of dust control systems for rock drills, including 

deck shrouds for the drill bit and the discharge or dump shroud. 

The dust collection systems are most effective 

when good design and maintenance practices 

are implemented by skilled and properly trained 

operators.

• Deck Shroud Design. Use a one-piece shroud

that fully encloses the area around the drill bit.

Repair or replace torn or missing pieces and

make sure that gaps are sealed.

• Adequate Airflow. The dust collector should be

designed to draw more air than the bailing air

used to flush out cuttings from the drill hole. The

dust collector air volume should be three times

the bailing air volume.

• Water Injection at Dust Collector Exhaust. Adding

small amounts of water into the air discharge

duct can significantly reduce the release of silica

dust in the dump area. When adding water to

the discharge duct, slowly increase the rate until

there is no visible dust. Check the duct interior

daily and clear dust deposits that may form in it.

• Fan Exhaust Placement. Extend the dust

collection system exhaust port so that the dusty

air releases away from workers. Clogged ducts

and filters restrict dust collector airflow. Remove

dust that collects on filters and in flexible ducts.

• Fan Maintenance. Dust can damage the fan

motor, blades, and drill bits. Replace worn

parts. Check for excessive vibration in fan

belts, coupling, and belt alignment, and worn

or broken belts, blades, mounting bolts, and

bushings. Repair and maintain as needed.

• Filters. Replace clogged or damaged air filters

and avoid exposure to dust when cleaning or

replacing filters.

FactSheet
Operator Isolation/Wet Methods

The alternative to using a dust-collection system 

is operator isolation in an enclosed cab or booth, 

along with applying water to the drill bit during 

cutting to reduce dust.

Drill operators using vehicle-mounted rigs with 

enclosed cabs can reduce their silica exposure by 

staying inside the cab during drilling. The cab must:

• Be well-sealed and well-ventilated using 

positive pressure.

• Have door jambs, window grooves, powerline 

entries, and other joints that work properly and 

are tightly sealed.

• Have heating and air conditioning so that 

operators can keep windows and doors closed.

• Use an intake air filter with a minimum MERV-16 

rating (at least 95% in the 0.3-10.0μm range).

• Be kept free from settled dust by regular 

cleaning and maintenance to prevent dust from 

become airborne inside the enclosure.

Photo courtesy of NIOSH

Vehicle-mounted drilling rigs with dust collection system

around drill bit and low-flow water spray to wet the dust

discharged from the dust collector. The enclosed operator’s 

cab is on the right. The dust collection system is on the left. 

In wet drilling systems that use forced air (bailing 

air) to flush cuttings from the hole, water is added 

to the bailing air at the drill head. Small particles 

join to form larger particles, thus reducing 

escaping respirable dust. The proper use of wet 

methods requires a trained and skilled operator. 

Too much water can create mud slurry at the 

bottom of the hole that can trap the bit, coupling, 

and steel extensions. Too little water will not 

effectively control escaping dust.

Respiratory Protection

When properly used, dust collection systems and 

operator isolation can effectively control exposure 

to silica dust.

Therefore, this Table 1 entry does not require 

the use of respiratory protection when operating 

drilling rigs equipped with a dust collection system 

or from within an enclosed cab.

Additional Information

For more information, visit www.osha.gov/silica

and see the OSHA Fact Sheet on the Crystalline 

Silica Rule for Construction, and the Small Entity 

Compliance Guide for the Respirable Crystalline 

Silica Standard for Construction.

OSHA can provide compliance assistance 

through a variety of programs, including technical 

assistance about effective safety and health 

programs, workplace consultations, and training 

and education. OSHA’s On-Site Consultation 

Program offers free, confidential occupational 

safety and health services to small and mediumsized businesses in all states and several territories 

across the country, with priority given to highhazard worksites. On-Site consultation services 

are separate from enforcement and do not result 

in penalties or citations. To locate the OSHA 

On-Site Consultation Program nearest you, visit 

www.osha.gov/consultation.

How to Contact OSHA

Under the Occupational Safety and Health Act 

of 1970, employers are responsible for providing 

safe and healthful workplaces for their employees. 

OSHA’s role is to ensure these conditions for 

America’s working men and women by setting 

and enforcing standards, and providing training, 

education and assistance. For more information, 

visit www.osha.gov or call OSHA at 1-800-321-

OSHA (6742), TTY 1-877-889-5627.

DSG FS-3931 12/2017

This is one in a series of informational fact sheets highlighting OSHA programs, policies or 

standards. It does not impose any new compliance requirements. For a comprehensive list of 

compliance requirements of OSHA standards or regulations, refer to Title 29 of the Code of Federal 

Regulations. This information will be made available to sensory-impaired individuals upon request. 

The voice phone is (202) 693-1999; teletypewriter (TTY) number: (877) 889-5627.