Silica Dust and Concrete Grinding and Polishing: Air Exposure Monitoring and OSHA Permissible Exposure Limits (PELs):

 

Miner wearing a respirable silica dust air sampling device A hard-rock, miner wearing a respirable, silica dust air sampling device for his entire work shift (8, 10 or 12 hours). The yellow banded cassette (left side, right lapel) holds a membrane filter that is the “air sample”. This cassette is analyzed for respirable silica by a laboratory that is accredited by the AIHA.

Grinding and polishing of concrete will release the dangerous silica-bearing dust in to air, exposing construction workers and others. Personal exposure monitoring should be performed to document the concentration of the amount of silica in the personal breathing zone of the worker (Photo #s 1-2). The air sampler will only measure the very small, “respirable” dust particles, and the laboratory analysis will measure the amount of silica (also known as crystalline silica, or quartz) in the air sample. Only the very small, “respirable” silica dust particles are deposited in the deep parts of the lung and can lead to the development of silicosis and lung cancer.

Measuring the amount of silica in the air is described in detail in the web-based OSHA silica advisor.

The laboratory will determine the concentration of respirable dust in the air sample in milligrams of respirable dust per cubic meter of air (mg/m3). The laboratory will then digest the membrane filter, and measure the percentage of silica in the overall amount of dust on the filter, and report a value of % silica (also known as quartz).

Personal air sampling pump A personal air sampling pump (black, left) that moves air through a Dorr-Oliver, 10 mm nylon cyclone and a filter cassette (yellow). The cyclone spins and removes the large dust particles from the air sample, and only allows those that are roughly less than 10 um in diameter (“respirable”) particles to enter into the filter cassette (yellow). The cyclone and filter cassette are placed into a calibration chamber (clear plastic). The entire air sampling train is then connected to a calibration device (top center, blue) to ensure the proper flow rate of air of 1.7 liters of air per minute (1.7 L/min). 

By knowing the air sampling time on the worker, e.g. 480 minutes, and the laboratory’s measurement of the weight of the dust (milligrams) and the percentage of silica in the dust, the OSHA PEL and the actual exposure can be calculated, as well as the severity of the exposure (exposure/PEL), with ratios greater than 1.0 being in excess of the PEL. 

Comparing the dust exposure to the OSHA limit is also described in detail in another section of the web-based OSHA silica advisor.

Even if little visible concrete dust is present in the air, the silica levels may exceed the OSHA permissible exposure limit. Dry polishing should be avoided unless exposure monitoring (air sampling) confirms that the vacuum and filtration systems are effective. Suppression of the dust with wet-methods is the age-old choice of control of silica-bearing dust. 

By controlling the release of the dust into the air, the workers exposure is minimized, and the dangerous, insidious disease can be prevented. OSHA inspectors will force the use of effective dust suppression work practices, and only allow personal respiratory protection as an interim method of control.

Author:
Harry J. Beaulieu, PhD, CIH, CSP

President and Senior Scientist
Industrial Hygiene Resources

Benefits of Polished Concrete

Health Issues

LEED US Green Building Council

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