Engineering Controls for Silica in Construction

Cut-off saws (also known as hand-held abrasive cutters, chop saws, and quickie saws) are used extensively throughout the construction industry. They are frequently used without dust controls to cut brick, concrete slabs, block and pavers which typically contain crystalline silica. Cutting those masonry materials without dust controls can surround the worker in a cloud of dust that contains respirable crystalline silica (RCS).

The video below shows the potential exposure that results when cutting a concrete block without dust controls. The worker’s respirable dust exposure is shown in the bar at the right. The units are milligrams of respirable dust per cubic meter of air.

Cut-off Saw without Engineering Controls
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(rm 4 kb)

Two types of engineering controls are available to reduce dust exposures from cutting masonry with a cut-off saw. The first type of control uses water to suppress the dust. The second used local exhaust ventilation to capture dust at its source. Both types of control are described below. Each description is followed by a video that demonstrates the effectiveness of the dust control.

1. Dust suppression with water

Water may be used to suppress dust produced by pneumatic, hydraulic, or gasoline-powered saws. Water is typically applied to the blade through one or two nozzles to suppress dust emissions. Water may be supplied from a portable pressurized tank or a hose. The recommended flow rate is 0.5 liters (17 ounces) of water per minute to suppress dust. Less water will not be as effective. More water will not increase dust control. Electric-powered saws with water attachments are also available commercially.

The video below shows the same worker using a cut-off saw with dust suppression with water. The worker’s respirable dust exposure, shown in the bar at the right, is much lower than in the previous video.

Cut-off Saw with Water Controls
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(rm 4 kb)

2. Local exhaust ventilation

Local exhaust ventilation is used on hand-held concrete saws in the form of an exhaust hood (or shroud) that surrounds the blade. The hood is connected to an industrial vacuum cleaner by a flexible hose. The vacuum cleaner produces suction to capture the dust at its source. The hood should be in close contact with the surface to be cut for best results. Adjustable hoods that can accommodate different cutting depths are preferred.

Vacuum Cleaners

The vacuum cleaner should have the following features:

• Sufficient flow rate to capture the dust and transport it to the vacuum source. One study showed that and air flow rate of 70 cubic feet per minute (cfm) was required to achieve effective dust control ^[1]
• A high-efficiency particulate air (HEPA) filter to reduce the chances of releasing dust containing RCS from the vacuum into the worksite.
• A pre-filter or cyclone to increase the length of service of the HEPA filter.
• A filter replacement indicator, such as a pressure gauge. If the vacuum cleaner does not have a pressure gauge, workers can monitor the air flow by checking to see if a dust plume is escaping from around the shroud.
• The ability to clean and replace filters and full collection bowls or bags without exposing the operators to dust.
• A motor that draws at least 10 amps.

Hose

A 2-inch diameter hose with a smooth interior and a length of no more than 15 feet provides adequate air flow to capture and transport the dust. The hose should have as few elbows or turns as possible.

The following video shows the worker using a cut-off saw with local exhaust ventilation. The bar on the right shows that the worker’s respirable dust exposure is even lower when compared to the dust suppression with water method.

Cut-off Saw with Vacuum Controls
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(rm 79 bytes)

For more information about dust controls for cut-off saws see:

1. Croteau GA, Guffey SE, Flanagan ME, Seixas NS. (2002) The effect of local exhaust ventilation controls on dust exposures during concrete cutting and grinding activities. Am Ind Hyg Assoc J; 63: 458-67. ( PDF 354 kb )

2. Thorpe A, Ritchie AS, Gibson MJ, Brown RC (1999). Measurements of the effectiveness of dust control on cut-off saws used in the construction industry. Annals of Occupational Hygiene. 43 (7): 433-456. ( PDF 314 kb )

3. Health and Safety Executive (HSE) (2008). Time to Clean the Air! Protect your lungs when using cut-off saws (Leaflet). ( PDF 213 kb )

4. Echt A, Lefkowitz D, Meeker J, Susi P, Cardwell B, Heitbrink WA (2007). In-dept survey of dust control technology for cutting concrete block and tuckpointing brick at The International Masonry Institute Bordentown Training Center, Bordentown, NJ. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Report No. EPHB 282-13. ( PDF 624 kb )

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