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Emerging issue: ultrafine particles from coarse silica gel as a potential inhalation hazard.

Martin J; Hoover M; Cocalis J
American Industrial Hygiene Conference and Exposition, June 1-6, 2002, San Diego, California. Fairfax, VA: American Industrial Hygiene Association, 2002 Jun; :95
Silica gel is not known to produce significant disease or toxic effects when total dust exposures are kept under 10 mg/m3. In response to a worker inquiry as to whether silica gel desiccant used in a well-ventilated confined space could cause or exacerbate small air-ways disease, NIOSH obtained a bulk sample of the silica gel desiccant for analysis by scanning electron microscopy. Photomicrographs showed the dominant particles to be greater than 200-400 micrometers in diameter, which by definition are non-inhalable and would not relate to small airways disease. A closer look at the SEM samples revealed that the surfaces of the large particles were littered with smaller particles. Most were less than a micrometer in diameter and some were smaller than 0.2 um. If detached, these particles could penetrate into the small airways. Mild agitation of the bulk silica gel produced a visible plume similar in appearance to that of a fine aerosol. Plume samples revealed ultrafine particles with exponentially more surface area per unit mass than the coarse particles. Some of the fine particulate was fiber-like in shape. The particles were found to be amorphous, not crystalline. This ultrafine component may have differing toxicity and exposure potential than the coarse particulate. For example, coarse particles of titanium dioxide are not associated with toxic effects, but ultrafine particles of titanium dioxide cause severe lung injury. The presence of an ultrafine component to coarse silica gel powders indicates the need for adequate engineering controls and respiratory protection when handling these materials. Additional evaluations, including inhalation toxicology studies are needed to determine whether ultrafine silica particles pose a special hazard.
Particulate-dust; Particulates; Silica-dusts; Silicates; Inhalation-studies; Hazards; Dust-exposure; Dust-inhalation; Dusts; Sampling; Nanotechnology
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American Industrial Hygiene Conference and Exposition, June 1-6, 2002, San Diego, California
Page last reviewed: May 11, 2023
Content source: National Institute for Occupational Safety and Health Education and Information Division