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Criteria for a Recommended Standard: Occupational Exposure to Refractory Ceramic Fibers

May 2006
DHHS (NIOSH) Publication Number 2006-123
Cover of NIOSH document number 2006-123

This criteria document is derived from reviews of information from human and animal studies of the toxicity of refractory ceramic fibers (RCFs) and is intended to describe the potential health effects of occupational exposure to airborne fibers of this material. RCFs are amorphous synthetic fibers produced by the melting and blowing or spinning of calcined kaolin clay or a combination of alumina, silica, and other oxides. RCFs belong to the class of synthetic vitreous fibers (SVFs)-materials that also include fibers of glass wool, rock wool, slag wool, and specialty glass. RCFs are used in commercial applications requiring lightweight, high-heat insulation (e.g., furnace and kiln insulation). Commercial production of RCFs began in the 1950s in the United States, and production increased dramatically in the 1970s. Domestic production of RCFs in 1997 totaled approximately 107.7 million lb. Currently, total U.S. production has been estimated at 80 million lb per year, which constitutes 1% to 2% of SVFs produced worldwide. In the United States, approximately 31,500 workers have the potential for occupational exposure to RCFs during distribution, handling, installation, and removal. More than 800 of these workers are employed directly in the manufacturing of RCFs and RCF products. With increasing production of RCFs, concerns about exposures to airborne fibers prompted animal inhalation studies that have indicated an increased incidence of mesotheliomas in hamsters and lung cancer in rats following exposure to RCFs. Studies of workers who manufacture RCFs have shown a positive association between increased exposure to RCFs and the development of pleural plaques, skin and eye irritation, and respiratory symptoms and conditions (including dyspnea, wheezing, and chronic cough). In addition, current and former RCF production workers have shown decrements in pulmonary function.

Criteria for a Recommended Standard: Occupational Exposure to Refractory Ceramic Fibers

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