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December 21, 2004 7:30 AM CST

Beware of Crystalline Silica Dust

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Worker exposure to crystalline silica dust continues to be a health hazard associated with the construction industry. Understanding the importance of respiratory protection for masons is more readily apparent if you remember that damage from low exposures may not present itself for years, until it's too late.

Construction-related activities that may produce crystalline silica-containing dust include abrasive-blasting, tuckpointing, cutting of concrete or masonry products, demolition and repair of concrete or masonry structures, and dry sweeping or pressurized air blowing of concrete, rock or sand dust. To put things into perspective, the simple cutting of dry block or concrete can result in exposures approaching 10 times the Occupational Safety and Health Administration's (OSHA) established permissible exposure limit (PEL) for crystalline silica.

Several types of respirators provide varying levels of protection against silica dust. The choice of respirator depends on the level of exposure. All respirators, however, including disposable dust masks, must be approved by the National Institute of Safety and Health (NIOSH).

As the atmospheric concentration of crystalline silica increases, the assigned protection factor (APF) ? defined as the ratio of the concentration of the contaminant outside of the respirator to the concentration of the contaminant inside of the respirator ? generally increases. When tested at the NIOSH-certification conditions, an N95 and N100 filter will remove at least 95% and 99.97%, respectively, of a solid particulate contaminant from an inspired air stream. Type H and P100 high efficiency filters will remove at least 99.97% of solid particulates and an oily mist aerosol from an inspired air stream.

Half-mask respirators equipped with particulate filters are suitable for use against all forms of respirable crystalline silica at concentrations of 0.5 mg/m3 or less. They are also suitable for use against amorphous silica dust at concentrations as great as 60 mg/m3.

29 CFR 1926.55 (Safety and Health Regulations for Construction: Gases, Vapors, Fumes, Dusts and Mists) states that to achieve compliance with the established OSHA PELs, the employer must first implement engineering (e.g., dust suppression) or administrative controls (e.g., job rotation) whenever feasible.

When such measures are not feasible or do not result in full compliance, protective equipment, including respiratory protection devices, must be used to keep employee exposure to air contaminants below the PEL. When respirators are used, employers are required to establish a comprehensive respiratory protection program as outlined in the Respiratory Protection Standard (29 CFR 1910.134) or 29 CFR 1926.103 (which refers to 29 CFR 1910.134). The Respiratory Protection Standard provides clear guidance for establishing and implementing a respirator program.

Additional guidance can be found in the "American National Standard Practices for Respiratory Protection," ANSI Z88.2 (refer to latest edition).


About the Author

Zane N. Frund, Ph.D. is the Manager of Chemical Research and Analytical Services for MSA Company.

 

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