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Abstract
This paper provides a review of the relevant literature on refractory ceramic fibers (RCFs), summarizing relevant data and information on the manufacture, processing, applications, potential occupational exposure, toxicology, epidemiology, risk analysis, and risk management. RCFs are amorphous fibers used for high-temperature insulation applications. RCFs are less durable/biopersistent than amphibole asbestos, but more durable/biopersistent than many other synthetic vitreous fibers (SVFs). Moreover, as produced/used, some RCFs are respirable. Toxicology studies with rodents using various exposure methods have shown that RCFs can cause fibrosis, lung cancer, and mesothelioma. Interpretation of these animal studies is difficult for various reasons (e.g., overload in chronic inhalation bioassays). Epidemiological studies of occupationally exposed cohorts in Europe and the United States have demonstrated measurable effects (e.g., mild respiratory symptoms and pleural plaques) but no disease (i.e., no interstitial fibrosis, no excess lung cancer, and no mesothelioma) to date. The RCF industry, working cooperatively with various government agencies in the United States, has developed a comprehensive product stewardship program (PSP) to identify and control risks associated with occupational exposure. One provision of the PSP is the adoption of a voluntary recommended exposure guideline (REG) of 0.5 fibers/milliliter (f/ml). Selected on the basis of prudence and demonstrated feasibility, compliance with the REG should reduce risks to levels between 0.073/1000 and 1.2/1000, based on extrapolations from chronic animal inhalation studies.
Acknowledgements
The assistance of Ron Niebo in the preparation of the manuscript is gratefully acknowledged. We also wish to acknowledge the constructive comments of two anonymous reviewers. Their suggestions and questions have undoubtedly improved the clarity of the manuscript.
Declaration of interest
This work was supported by Unifrax Corp., Niagara Falls, NY. However, the findings and conclusions are those of the authors alone and do not necessarily represent those of Unifrax Corp.
Notes
1German regulatory authorities dispute this assertion and argue that IP is the appropriate method of administration.
2An interesting article by Bernstein et al. (Citation2008) indicated that adding particles to chrysotile fibers did not retard the rate of clearance or induce histopathological changes. These authors concluded that the fine particles deposited in the lung accelerated the recruitment of marcophages and decreased the number of fibers across all size ranges remaining in the lung.
3Dyspnea grade 1 included all grades of shortness of breath upon exertion. Dyspnea grade 2 included all grades of shortness of breath upon exertion, excluding shortness of breath when hurrying on the level or walking up a slight hill.
4Recurrent chest illness was defined as a positive response to the question “During the past 3 years have you had any chest illnesses that have kept you off work?”, if the worker reported two or more chest illnesses.
5Via a surgical incision in the chest wall.
6Via use of a thin, lighted tube (called an endoscope) to examine the inside of the chest.
7Common confounders include fat pads, intrathoracic muscles, companion shadows, tuberculosis, rib fractures, and other pneumoconioses (see, e.g., Hillerdal, 2001).
8The ratio of the standard deviation σ to the mean µ of the time-weighted average fiber concentrations.
9See http://eur-lex.europa.eu/smartapi/cgi/sga_doc?smartapi!celexapi!prod!CELEXnumdoc&lg=EN&numdoc=31997L0069&model=guichett. Specifically Nota Q states: “The classification as a carcinogen need not apply if it can be shown that the substance fulfils one of the following conditions: a short-term biopersistence test by inhalation has shown that the fibres longer than 20 μm have a weighted half life less than 10 days, or a short-term biopersistence test by intratracheal instillation has shown that the fibres longer than 20 μm have a weighted half life less than 40 days, or an appropriate intra-peritoneal test has shown no evidence of excess carcinogenicity, or absence of relevant pathogenicity or neoplastic changes in a suitable long term inhalation test.”
10These documents are available electronically at http://www.ecfia.eu/00_files/04/ww_HTIW_english.pdf and http://www.ecfia.eu/00_files/04/2007-11-code-of-practice.pdf.