Solution Summary: Walk-Behind Concrete Scarifiers with Wet Dust Suppression
Walk-behind scarifier with wet dust suppression reduces dust during concrete roughening, coating removal and surface preparation.
Description:
Walk-behind concrete scarifiers or milling machines are used to roughen concrete, remove coatings or high spots and prepare concrete for coatings or resurfacing. The use of concrete scarifiers generates a large amount of dust that may contain high levels of crystalline silica and creates a hazard for everyone in the vicinity. Concrete scarifiers with wet dust suppression is an engineering control option. These machines have a rotating drum with flails or multi-tipped cutting wheels mounted on the drum that is partially enclosed to allow for the suppression of dust created by the scarifying process. Water is misted onto the drum and concrete surface while it is being cut, suppressing dust at the point of generation. The concrete dust is then contained within a slurry, reducing the concentration in the worker's breathing zone.
The following examples of commercially available walk-behind scarifiers with optional wet dust supression systems are manufactured by EDCO, Inc. The company recommends the CPM-8 models for "sidewalk trip hazard repair, concrete and coatings removal, floor cleaning or prepration, creating non-slip surfaces, and traffic line and markings removal." EDCO recommends the CPM-10 models for "aggressive removal of materials, production scarification and heavy coatings removal."
Edco Scarifiers
The Edco scarifiers use a standard hose connection to supply a water mist to the scarifiers’ drum and in front of the machine.
|
Model |
Costs |
Drum Width (inches) |
Revolutions per Minute |
Power Requirements |
Weight (pounds) |
Maximum Removal Rate |
|
CPM-8-5B |
$3,600 - 4,000 |
8 |
2130 |
230 volts, 19.5 amps or 230 volt, 12 amps (3 phase) |
220 |
350 – 500 |
|
CPM-8-9H |
$4,200 |
8 |
2150 |
Gasoline Powered, 9 Horsepower |
190 |
350 – 500 |
|
CPM-10-7.5B |
$4,300 |
10 |
2344 |
230/460 volts, 17.4/8.7 amps (3 phase) |
287 |
500 – 700 |
|
CPM-10-13H |
$5,100 |
10 |
2446 |
Gasoline Powered, 13 Horsepower |
267 |
500 – 700 |
(costs verified 1/2012)
- 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)
Risks Addressed:
Silica dust exposure may cause silicosis or lung scarring with prolonged exposure. Silicosis is an incurable, sometimes fatal, disease. The NIOSH Recommended Exposure Limit (REL) is 0.05 mg/m3 as a time-weighted average concentration for up to a 10-hour workday during a 40-hour workweek. This is one-fourth of the current OSHA standard, but still twice the ACGIH recommended Threshold Limit Value (TLV) of 0.025 mg/m3. In August 2013, OSHA proposed a revised silica standard of 0.05 mg/m3. Silica has also been associated with lung cancer and chronic obstructive pulmonary disease (COPD) (Rice, 2002).
Echt et al. conducted a study to determine respirable dust and silica concentrations while using a walk-behind concrete scabbler, a machine with similarities to a scarifier, during parking deck construction. Ten personal breathing zone samples were collected while the scabbler was used without dust controls. Five of the samples contained less respirable silica than the method can reliably detect (possibly due to wind or blockage of the sampler inlet by the worker’s clothing). The remaining five sample results were well above the NIOSH REL and ACGIH TLV for respirable silica and ranged from 0.48 to 2.1 mg/m3 (Echt, 2002).
Silicosis symptoms include: chronic cough, shortness of breath when exercising, severe breathing difficulty, weight loss and fever. People with silicosis are also at a high risk for developing tuberculosis (TB). Although there is no specific treatment for silicosis, the source of the silica must be removed in order to ensure the disease does not get worse (PubMed, 2009).
How Risks are Reduced:
Walk-behind concrete scarifiers have a rotating drum with flails or multi-tipped cutting wheels mounted on the drum. The drum is partially enclosed and water is sprayed onto the drum and concrete surface while it is being cut. Water combines with particles near the point of dust generation and, due to increased weight, the now larger particles settle to the ground and the level of airborne dust and exposures are reduced. As long as the dust and silica do not become airborne, the hazard is reduced. Silica and dust are only hazardous if inhaled and are not hazardous for skin contact.
Using wet dust suppression will visibly reduce dust, but the extent that this specific control reduces the small, respirable particles is unclear, without testing. Although exposure is not reduced to zero, substantial reduction is expected. This is dependent on the machine’s ability to provide and maintain adequate water flow for the task, the shroud configuration, the work rate and the extent to which workers are exposed to re-suspended dust. While there are no published sampling data on these specific tools, testing of scabblers, similar machines, indicates exposure to respirable dust and silica can be significantly reduced through the use of wet dust control.
The use of wet dust controls has been proven effective for concrete surface scabbling, a process with similarities to scarifying, during use in a parking deck construction project. The attachment was designed and built by the site superintendent in order to control dust created by the milling process. Compared to uncontrolled scabbling, the wet dust control reduced respirable dust concentrations by 80%, and all respirable silica concentrations were below the limit of detection (LOD) of 0.02 milligrams per sample (Echt, 2002).
Effects on Productivity:
Wet dust suppression should have a positive effect on productivity and definitely improve the quality of the work by removing large amounts of dust from the air, which provides a cleaner environment for operators. The reduction of airborne dust 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 suppressors 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. Cleaning up the concrete slurry while it is wet is important to prevent it from drying and become airborne dust. The amount of additional time this takes will depend on the amount of milling being done and the method of clean-up. Workers will need to adapt to working on wet floors. In addition, gaining access to electricity or a water source may impact productivity.
Additional Considerations:
The use of water controls may result in wet and slippery ground and walking surfaces. During cold weather this may lead to the formation of ice and an increased risk of slips, trips and falls. Concrete debris that is not removed from the work area while wet may become airborne once dried, posing an inhalation hazard to anyone in the area. Maintaining a work area free of debris and excess water will reduce the risk of these hazards.
The use of water as a dust control increases the risk of shock when electricity is used in the same area. Electrical cords and extensions must be rated for the tool's power requirements, be regularly inspected, and used in combination with ground fault interrupt circuits.
Large electric equipment commonly requires electrical circuits that can provide greater than 20 amps and more than 120 volts.
The use of gasoline-powered 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 or milling machines can generate hazardous sound levels that are greater than 90 decibels, the OSHA Permissible Exposure Limit (PEL). Hearing protection should be worn when using concrete scarifiers or milling machines 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 the manufacturer’s safety recommendations and comply with any applicable local, state or federal regulations.
Availability
Pullman-Ermator, Inc.
To obtain information, visit single phase electric dust extractorsp://www.ermatorusa.com
or contact 1-855-736-2869 hcpcustomer.service@husqvarna.com
Edco Scarifiers
To obtain information, visit http://edcoinc.com
or contact 1-800-638-3326 info@edcoinc.com
