Removing, roughening or resurfacing concrete with a walk-behind scarifier or milling machine generates a large amount of dust that may contain high levels of crystalline silica or other hazardous materials and creates a hazard for everyone in the vicinity. Vacuum dust controls are available for walk-behind concrete scarifiers.

These controls consist of a vacuum with a disposable filter (a high efficiency particulate air, HEPA, when practical) attached to a shroud surrounding the heads. The vacuum draws dust from the heads, the point of dust generation, and transports it to the collection unit. Capturing dust containing silica near the point of generation and removing it from the work environment reduces the concentration in the worker's breathing zone.

Cyclonic pre-separators, either as an integral part of the vacuum or as a separate unit, should be used to collect the majority of the particles before they reach the filters. Cyclonic pre-separators reduce the amount of dust that collects on the filter, which increases the useful life of expensive filters and helps to maintain the vacuum’s initial airflow rate. 

OSHA recommends using systems to capture and control concrete dust; vacuum dust collectors are the most common. These methods can remove most airborne dust particles generated by milling. Using a cyclonic separator and a vacuum with filters greatly reduces the risk to operators and other workers on a site.
 

Edco Scarifiers

The Edco scarifiers use a vacuum port to remove dust from the scarifier’s drum.

• Removal Depth per Pass: 1/8 inch
• Sound Pressure Level: greater than 90 dBA (OSHA’s Permissible Exposure Limit for an 8-hour time-weighted average is 90 dBA)
   

Edco Vacuum Systems

• Cast-composite material guaranteed for life not to crack
• Differential pressure gauge to indicate when filters should be replaced
• HEPA filter capable of removing 99.97% of 0.3 micron particles (the most penetrating size)
• Vacuum Port Diameter: 3 inches
   

Kut-Rite Scarifiers

The Kut-Rite scarifiers use a swiveling vacuum port for dust collection and are designed to be paired with a Klean-Rite vacuum system.

• Removal Depth per Pass: 1/8 inch
• Sound Pressure Level: not available but likely to exceed 90 dBA (OSHA’s Permissible Exposure Limit for an 8-hour time-weighted average)
   

Klean-Rite Vacuum Systems

• Collection Capacity: up to 70 pounds
• Filtration: filters feature Ultra-Web technology that enables the reverse flow units to work at maximum
• Vacuum Port Diameter: 3 inches
   

Smith Scarifiers

• Sound Pressure Level: greater than 90 dBA (OSHA’s Permissible Exposure Limit for an 8-hour time-weighted average is 90 dBA)
   

Smith Vacuum Systems

• Power Requirements: 220 volts, single phase, 20 amps
• Airflow: 330 cubic feet per minute
• Maximum Static Pressure: 118 inches of water
• Filtration: cyclonic pre-separator (MV-1000S only), cyclonic separator inside vacuum, and HEPA filter capable of removing 99.97% of 0.3 micron particles (the most penetrating size)
• Filter Cleaning: automatic shaking
• Sound Pressure Level: 75 dBA (OSHA’s Permissible Exposure Limit for an 8-hour time-weighted average is 90 dBA)

Descobrader Model 120.223 Scarifier

• Drum Width: 5.25 inches
• Power Requirements: 220 volts, 16 amps
• Maximum Removal Rate: 400 square feet per hour
• Removes up to 0.5 inches thick
• Vacuum Port Diameter: 3 inches
• Sound Pressure Level: not available but likely to exceed 90 dBA (OSHA’s Permissible Exposure Limit for an 8-hour time-weighted average)

Blastrac BMP-335EHY Scarifier

The Blastrac BMP-335EHY scarifier is optimally paired to a Blastrac BDC-3140DBP vacuum system.

• Drum Width: 13.2 inches
• Revolutions per Minute: 1,000
• Power Requirements: 460 volts, 32 amps, 3 phase
• Weight: 895 pounds
• Maximum Removal: 570 square feet per hour
• Removal Depth per Pass: 1/8 inch
• Sound Pressure Level: not available but likely to exceed 90 dBA (OSHA’s Permissible Exposure Limit for an 8-hour time-weighted average)
   

Blastrac BDC-3140DBP Vacuum System

• Power Requirements: 230 volts, 15.6 amps, 3 phase (single phase option)
• Collection Capacity: up to 200 pounds
• Filtration: HEPA filter capable of removing 99.97% of 0.3 micron particles (the most penetrating size)
• Filter Cleaning: automatic air-pulse cleaning system
• Maximum Static Pressure: 90 inches of water
• Airflow: 300 cubic feet per minute
• Weight: 507 pounds
• Vacuum Port Diameter: 2, 2.75, and 3 inches

Pullman-Ermator USA Single Phase Electric Dust Extractors

 (Photo courtesy of Husqvarna AB Construction Division)

• Dust Collection: Longopac® bag system (except for S1400) which uses a 70 foot long plastic tube that is divided and sealed at the desired length
• Filtration: cyclonic separator, coarse filter and HEPA filter capable of removing 99.97% of 0.3 micron particles (the most penetrating size)
• Sound Pressure Level: 75 dBA or less (OSHA’s Permissible Exposure Limit for an 8-hour time-weighted average is 90 dBA)

** Greater area allows more time between filter cleaning or replacement

Pullman-Ermator USA Three Phase Electric Dust Extractors

 (Photo courtesy of Husqvarna AB Construction Division)

• Filtration: cyclonic separator, coarse filter and HEPA filter capable of removing 99.97% of 0.3 micron particles (the most penetrating size)
• Dust Collection: Longopac® bag system which uses a 70 foot long plastic tube that is divided and sealed at the desired length
• Maximum Static Pressure: 110 inches of water
• Sound Pressure Level: 75 dBA or less (OSHA’s Permissible Exposure Limit for an 8-hour time-weighted average is 90 dBA)

* Greater area allows more time between filter cleaning or replacement

Pullman-Ermator USA Cyclonic Pre-Separators

(Photo courtesy of Husqvarna AB Construction Division)

• Removes approximately 90 percent of particulates and can be used with Pullman-Ermator or other dust extractors
• Dust collection: Longopac® bag system, which uses a 70 foot long plastic tube that is divided and sealed at the desired length

(Photo courtesy of Husqvarna AB Construction Division)

Vacuum dust collectors are expected to have a positive effect on productivity and improve the quality of the work by removing large amounts of dust, which provides a cleaner environment for operators and reduces the effort and time required for clean-up.  Dust capture avoids exposing other workers, members of the public, adjacent property, cars and building occupants, which can increase liability and time-consuming disputes.  Improved worker comfort is a result of reduced airborne dust which may in turn result in less fatigue for the worker and greater productivity.  In some cases, particularly where work is intermittent or in an area with general ventilation, use of dust collectors may be adequate to reduce the need to wear a respirator, and the need for an employer’s respiratory protection program. 

Some additional issues should be considered.  Changing vacuum bags takes time, which will depend on the amount of milling being done and the size of the vacuum bag or hopper.  Workers will need to adapt to working with a vacuum hose attached to the tool.

Ventilation for construction tools is often misunderstood. These are some key concepts that can help:

• The vacuum must be located as close to the dust generation as possible to be effective.  A shroud is needed to contain the dust so the vacuum can capture it.  The shroud must be kept as close to the work surface as is practical to provide adequate dust capture.
• The particles that can do the most damage in the lungs are small enough to penetrate the filters found on many shop vacuums.  Additionally, some inexpensive shop vacuums pull the dust through the motors, which can destroy the vacuum on really dusty jobs, eliminating any initial cost savings.
• For dust containing harmful particles like silica, it is important to use as high efficiency filters as practical.  The best available are called HEPA (high efficiency particle air) filters because they capture 99.97% of 0.3 micron particles (the most penetrating size).  But HEPA filters also create a greater pressure drop and decrease in air flow rate because it is more difficult to pull air through these denser filters so capture velocity may be reduced.  They also require pre-filters to extend the life of the HEPA filters, which are more expensive than other filters.
• For operations that generate large amounts of dust, a cyclonic collection unit may be the best solution.  Cyclonic collection units spin the particles and drop them into plastic bags.  The plastic bags are less expensive than many vacuum bags and the bags need to be replaced far less frequently because loading of the bags does not cause a pressure drop.
• Vacuum performance must be monitored on a regular basis.  For high dust generating tasks, dust caked on the filter may reduce flow to a level where it no longer provides adequate dust capture.  Automatic and manual filter shakers, coarse pre-filters and cyclonic collection units are available with some vacuums and may help maintain the air flow rate.

Large electric vacuums commonly require electrical circuits that can provide greater than 20 amps and/or more than 120 volts.  Cords and extensions must be rated for the tool's power requirements, be inspected regularly and used in combination with ground fault interrupt circuits.

The use of diesel and particularly gasoline-powered generators and equipment poses the risk of carbon monoxide exposure, especially in areas where airflow is reduced.  Steps to control exposure are important because the gas is invisible, odorless and tasteless.  Poisoning by carbon monoxide can occur quickly indoors, but working outdoors does not ensure operators won’t be overcome.  Small, inexpensive personal monitors should be worn by the operator to warn of unacceptable exposures.  Equipment should not be left idling to cut down on carbon monoxide and to conserve fuel.

Concrete scarifiers and milling machines can generate sound levels that are greater than 90 decibels, the OSHA Permissible Exposure Limit (PEL), and hazardous.  Hearing protection should be worn when using concrete scarifiers unless an industrial hygienist has conducted noise monitoring and indicated that hearing protection is not required.

As is the case with any construction equipment, users should follow manufacturer safety recommendations and comply with any applicable local, state or federal regulations.

Taylor Kingston and Michael R. Cooper - Aria Environmental, Inc.
Bruce Lippy - CPWR