Engineering Controls for Silica in Construction

Construction workers who perform concrete grinding may breathe dust that contains respirable crystalline silica (RCS). A NIOSH ^[7] study found that workers grinding concrete to smooth poured concrete surfaces were exposed to high levels of dust containing RCS, ranging from 35 to 55 times the NIOSH recommended exposure limit (REL). The video below shows a worker performing a task with a concrete grinder while the overlay shows consistently high levels of respirable dust in the air.

Concrete Grinder without Engineering Controls
To download, right click below
(rm 91 bytes)

Local exhaust ventilation systems (LEV) can be attached to concrete grinders to reduce RCS exposures. Researchers have found that levels of exposure to RCS were significantly lower when workers used a grinder equipped with an LEV system compared to a grinder used without LEV.

An LEV system consists of a grinder equipped with a ventilation shroud, a length of flexible hose, and a portable electric vacuum cleaner that acts as the fan and dust collector for the ventilation system. Some specifications for an LEV system for a concrete grinder are listed below.

Vacuum Cleaner The vacuum should have the following features: Sufficient flow rate to capture the dust and transport it to the vacuum source. 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. 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.

Figure 1. Grinder in use with the control in place.

Hose

The hose should have a diameter of 1.5- or 2-inches with a relatively smooth interior and a length of no more than 15 feet to provide adequate air flow.

Shroud

The type of shroud to be used depends on the preferences of the cement finisher and the employer, according to the task to be performed. After testing different types of shrouds, NIOSH determined that all were equally effective, reducing dust exposure by at least 90%.

The following video shows a worker using a concrete grinder with a LEV system. The left bar of the graphic overlay of the video shows low amounts of respirable dust when compared to the initial video (above).

Concrete Grinder with Engineering Controls
To download, right click below
(rm 88 bytes)

Dust controls in the form of local exhaust ventilation (LEV) systems offer several benefits. Those benefits include reducing worker exposure to hazardous dust, potentially allowing for use of less protective respiratory protection; reduced cleanup time; and reduced exposures during cleanup. The LEV dust control may greatly reduce worker exposures to hazardous dust. However, respirators are still necessary to reduce exposure to RCS below the NIOSH REL of 50µg/m³.

References:

1. Akbar-Khanzadeh F, Milz S, Ames A, Susi PP, Bisesi M, Khuder SA, Akbar-Khanzadeh A [2007]. Crystalline silica dust and respirable particulate matter during indoor concrete grinding—wet grinding and ventilated grinding compared with uncontrolled conventional grinding. Occup. Environ. Hyg 4:770–779.

2. CFR. Code of Federal regulations. Washington, DC: U.S. Government Printing Office. Office of the Federal Register.

3. Croteau GA, Flanagan ME, Camp JE, Seixas NS [2004]. The efficacy of local exhaust ventilation for controlling dust exposures during concrete surface grinding. Ann. Occup. Hyg 48(6):509–518.

4. Echt A, Seiber K [2002]. Control of silica exposure from hand tools in construction: grinding concrete. Appl Occup Environ Hyg 17(7):457–461.

5. Heitbrink WA, Collingwood S [2005]. Protecting tuckpointing workers from silica dust: draft recommendations for a ventilated grinder. The Center to Protect Workers’ Rights, Silver Spring, MD .

6. NIOSH [1996]. NIOSH Alert: Request for assistance in preventing silicosis and deaths in construction workers. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, DHHS (NIOSH) Publication No. 96–112.

7. NIOSH [2001]. In-depth survey report of four sites: exposure to silica from hand tools in construction chipping, grinding, and hand demolition at Frank Messer and Sons Construction Company, Lexington and Newport KY; Columbus and Springfield, OH. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Survey Report No. EPHB 247–15.

8. NIOSH [2002a]. NIOSH hazard review: Health effects of occupational exposure to respirable crystalline silica. 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. 2002–129.

9. NIOSH [2002b]. In-depth survey report of control of respirable dust and crystalline silica from grinding concrete at Messer Construction, Newport, Kentucky and Baker Concrete Construction, Dayton, Ohio. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Survey Report No. EPHB 247–21.

Tuckpointing

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