Background photo on cover by James Lockey, M.D.: Photomicrograph of a rat lung in inhalation studies with airborne fibers. Inset photo on cover, courtesy of Kevin H. Dunn: NIOSH industrial hygienist performing air sampling to evaluate engineering controls in simulated work ac- tivities using RCF materials. Criteria for a Recommended Standard Occupational Exposure to Refractory Ceramic Fibers DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Institute for Occupational Safety and Health This document is in the public domain and may be freely copied or reprinted. Disclaimer Mention of any company or product does not constitute endorsement by the National Institute for Occupational Safety and Health (NIOSH). In addition, citations to Web sites external to NIOSH do not constitute NIOSH endorsement of the sponsoring organizations or their programs or prod- ucts. Furthermore, NIOSH is not responsible for the content of these Web sites. Ordering Information To receive documents or other information about occupational safety and health topics, contact NIOSH at NIOSH Publications Dissemination 4676 Columbia Parkway Cincinnati, OH 45226–1998 Telephone: 1–800–35–NIOSH (1–800–356–4674) Fax: 1–513–533–8573 E-mail: [email protected] or visit the NIOSH Web site at www.cdc.gov/niosh DHHS (NIOSH) Publication No. 2006–123 May 2006 Safe • Healthier • PeopleTM ii Refractory Ceramic Fibers Foreword When the U.S. Congress passed the Occupational Safety and Health Act of 1970 (Public Law 91– 596), it established the National Institute for Occupational Safety and Health (NIOSH). Through the Act, Congress charged NIOSH with recommending occupational safety and health standards and describing exposure limits that are safe for various periods of employment. These limits in- clude but are not limited to the exposures at which no worker will suffer diminished health, func- tional capacity, or life expectancy as a result of his or her work experience. By means of criteria documents, NIOSH communicates these recommended standards to regulatory agencies (includ- ing the Occupational Safety and Health Administration [OSHA]), health professionals in academic institutions, industry, organized labor, public interest groups, and others in the occupational safety and health community. Criteria documents contain a critical review of the scientific and techni- cal information about the prevalence of hazards, the existence of safety and health risks, and the adequacy of control methods. 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)—ma- terials 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 insu- lation). 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 manufactur- ing 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 con- ditions (including dyspnea, wheezing, and chronic cough). In addition, current and former RCF production workers have shown decrements in pulmonary function. After evaluating this evidence, NIOSH proposes a recommended exposure limit (REL) for RCFs of 0.5 fiber per cubic centimeter (f/cm3) of air as a time-weighted average (TWA) concentra- tion for up to a 10-hr work shift during a 40-hr workweek. Limiting airborne RCF exposures to this concentration will minimize the risk for lung cancer and irritation of the eyes and upper Refractory Ceramic Fibers iii Foreword respiratory system and is achievable based on a review of exposure monitoring data collected from RCF manufacturers and users. However, because a residual risk of cancer (lung cancer and pleural mesothelioma) may still exist at the REL, continued efforts should be made toward reducing expo- sures to less than 0.2 f/cm3. Engineering controls, appropriate respiratory protection programs, and other preventive measures should be implemented to minimize worker exposures to RCFs. NIOSH urges employers to disseminate this information to workers and customers. NIOSH also requests that professional and trade associations and labor organizations inform their members about the hazards of exposure to RCFs. John Howard, M.D. Director, National Institute for Occupational Safety and Health Centers for Disease Control and Prevention iv Refractory Ceramic Fibers Executive Summary The National Institute for Occupational Safety lung cancer. However, studies of worker popu- and Health (NIOSH) has reviewed data char- lations with occupational exposure to airborne acterizing occupational exposure to airborne RCFs have shown an association between ex- refractory ceramic fibers (RCFs) and informa- posure and the formation of pleural plaques, tion about potential health effects obtained increased prevalence of respiratory symptoms from experimental and epidemiologic studies. and conditions (dyspnea, wheezing, chronic From this review, NIOSH determined that oc- cough), decreases in pulmonary function, and cupational exposure to RCFs is associated with skin, eye, and upper respiratory tract irritation adverse respiratory effects as well as skin and [Lemasters et al. 1994, 1998; Lockey et al. 1996]. eye irritation and may pose a carcinogenic risk Increased decrements in pulmonary function based on the results of chronic animal inhala- among workers exposed to RCFs who are cur- tion studies. rent or former cigarette smokers indicate an apparent synergistic effect between smoking In chronic animal inhalation studies, expo- and RCF exposure [Lemasters et al. 1998]. This sure to RCFs produced an increased incidence finding is consistent with studies of other dust- of mesotheliomas in hamsters [McConnell et exposed populations. The implementation of al. 1995] and lung cancer in rats [Mast et al. improved engineering controls and work prac- 1995a,b]. The potential role of nonfibrous par- tices in RCF manufacturing processes and end ticulates generated during inhalation exposures uses have led to dramatic declines in airborne in the animal studies complicates the issue of fiber exposure concentrations [Rice et al. 1996, determining the exact mechanisms and doses 1997; Maxim et al. 2000a], which in turn have associated with the toxicity of RCFs in produc- lowered the risk of symptoms and health ef- ing carcinogenic effects [Mast et al. 2000]. The fects for exposed workers. induction of mesotheliomas and sarcomas in rats and hamsters following intrapleural and In 2002, the Refractory Ceramic Fibers Coali- intraperitoneal implantation of RCFs pro- tion (RCFC) established the Product Steward- vided additional evidence for the carcinogenic ship Program (PSP), which was endorsed by potential of RCFs [Wagner et al. 1973; Davis the Occupational Safety and Health Admin- et al. 1984; Smith et al. 1987; Pott et al. 1987]. istration (OSHA). Contained in the PSP were Lung tumors have also been observed in rats recommendations for an RCF exposure guide- 3 exposed to RCFs by intratracheal instillation line of 0.5 fiber per cubic centimeter (f/cm ) of [Manville Corporation 1991]. air as a time-weighted average (TWA) based on the contention that exposures at this concen- In contrast to the carcinogenic effects of RCFs tration could be achieved in most industries observed in experimental animal studies, epide- that manufactured or used RCFs. At this time, miologic studies have found no association be- the available health data do not provide suf- tween occupational exposure to airborne RCFs ficient evidence for deriving a precise health- and an excess rate of pulmonary fibrosis or based occupational exposure limit to protect Refractory Ceramic Fibers v Executive Summary against lung cancer. However, given what is cancer are estimated to be between 0.03/1,000 known from the animal and epidemiological and 0.47/1,000 (based on extrapolations of risk data, NIOSH supports the intent of the PSP models from Moolgavkar et al. [1999] and Yu and concurs that a recommended exposure and Oberdörster [2000]). limit (REL) of 0.5 f/cm3 as a TWA for up to a 10-hr work shift during a 40-hr workweek Maintaining airborne RCF concentrations be- will lower the risk for developing lung cancer. low the REL requires a comprehensive safety