REFRACTORY CERAMIC FIBRES: THE MEASUREMENT AND CONTROL OF EXPOSURE

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1 PII: S (96)00121^» Ann. occup. Hyg., Vol. 41, Supplement 1, pp , Published by Elsevier Science Ltd on behalf of BOHS Printed in Great Britain. All rights reserved /97 $ Inhaled Particles VIII REFRACTORY CERAMIC FIBRES: THE MEASUREMENT AND CONTROL OF EXPOSURE C. G. Burley*, R. C. Brownf and L. D. Maxima "Carborundum Company, Rainford, St Helens, Merseyside, U.K.; f4 Bramble Close, Uppingham, Rutland; ^Everest Consulting, Cranbury, New Jersey, U.S.A. INTRODUCTION Refractory ceramic fibres (RCF) are vitreous aluminosilicates manufactured by melting alumina, silica and other materials; a stream of the molten material is either blown by high pressure air or directed onto a series of spinning wheels to form fibres which have a random diameter and length distribution. The industrial applications for which these materials are used require resistance to temperatures between 1000 and 1460 C, precluding the use of organic binders. For such temperatures fibres with median diameters typically between 1.5 and 3.0 urn are needed for efficient insulation. Many fibre types, including RCFs, injected or implanted into the pleural or peritoneal cavities of test animals can cause mesothelioma (e.g. Pott et al., 1987) and despite the rejection of intracavity experiments by most authorities (reviewed McClellan et al., 1992), the International Agency for Research on Cancer (IARC) classified man-made mineral fibres (MMMF), including RCF, as category 2B carcinogens: "possibly carcinogenic in humans" (IARC, 1988). As animal inhalation experiments had given inconclusive results (Davis et al., 1984; Smith et al., 1987) the MMMF industry carried out additional experiments most of which used RCFs (the so called "RCC" experiments reviewed by Bunn et al., 1993). However problems in interpretation remain (e.g. Brown et al., 1995). While positive results can be obtained in animal experiments studies of human populations exposed to RCFs have revealed no ill health (reviewed Glass et al., 1995). However the RCF industry remains determined to ensure the safest possible practices in the manufacture and use of its products and to do so in as public a way as possible; thus providing increasing reassurance to its workers, customers and regulators. METHODS The principal tool established by the manufacturers to ensure that RCF products will not present any unreasonable risk to human health or the environment is a comprehensive product stewardship programme (PSP) concerning the entire product life cycle from design, through manufacture, application to disposal of RCF materials. 267

2 268 C. G. Burley etal. This programme includes seven major areas; communication, health effects research, product research, special studies and three areas concerned with exposure. These three areas, exposure assessments, workplace monitoring and workplace controls, have been combined in Europe into the Ceramic Fibre Industries Association's (ECFIA's) controlled and reduced exposure (CARE) programme. Refractory ceramic fibres are generally used in industry, so that exposure to airborne fibre is more readily controllable than it would be if it were employed in consumer products. In North America and Europe only about people could be exposed to RCFs and these three facets of the PSP aim is to identify, quantify and control exposure in both manufacturing and user industries. The PSP arose from the industry's earlier work on measuring RCF exposure and recommending methods of control. While some countries had exposure limit values for RCFs ranging from 0.5 to 2 f cc" 1 in many there was no regulatory exposure limit. Therefore the RCF industry took the initiative and established an exposure guideline of 1 f cc" 1 (8 h time-weighted average). The industry then increased the collection of workplace monitoring samples, initially using various protocols and methods. During 1993 in the U.S.A. the industry and the EPA then constructed a voluntary consent in order to gather sufficient data to assess exposure in a statistically valid way. This data could then be used to monitor exposure reduction programmes and to enable the dissemination of the best available handling and use techniques. A standardised, protocol has been developed to collect the necessary data, the number of fibres in the air is measured for all types of task where exposure to RCFs could occur both "internally", in manufacturing plants and "externally" in customers' premises. As the aim is to get a statistically valid assessment of airborne fibre levels a random sampling strategy has to be used so that samples do not over represent worst- or best-case conditions with the consequent underestimated or exaggerated measure of exposure. Clearly the concentration of airborne fibre varies with the process being used, therefore, the various tasks involved in making and using RCFs have been classified and samples are taken in proportion to the number of people involved in each task. While each manufacturing plant can be sampled this is not possible for the greater number of customer's premises. Therefore, customers are selected for sampling in a way proportional to the amount of RCF purchased in the previous year. The selection process has also been weighted to ensure that measurements are made in all European countries; an identical programme in Australasia is also being integrated with that in Europe. In all countries the choice of premises and work stations to be sampled is being made by one of the present authors who is provided with confidential sales and production data by all manufacturers. All samples are taken and fibres counted using approved occupational hygiene methods and quality control so that the measurements always comply with the requirements of local regulatory authorities. Some customers wish to volunteer for sampling and measurements in these are in addition to those taken "at random". Some corrections for sampling and counting procedures will be made before all the data collected world-wide can be pooled. The results of this programme will be reported regularly to all interested parties including regulatory authorities and trades unions.

3 Refractory ceramic fibres 269 Table 1. Number of samples Number of samples per year in RCF per year in industries Job category manufacturing plants using RCFs Fibre production 70 Not applicable in manufacture only Finishing Sawing, grinding, sanding, die cutting, milling or routering Assembly Encapsulation/lamination, stapling, sewing, cutting, module manufacture, ball milling and dry mixing Mixing/forming Wet mixing, vacuum forming Auxiliary Maintenance, handling/shipping, cleanup, supervision, laboratory work Other Textile automotive and others n.e.c. Installation fitting, packing, wrapping, pounding, tamping and hardware installation Removal mould knockout, cleanup disposal, furnace maintenance Total Not applicable Not applicable RESULTS Tasks in the industry have been classified into 8 categories and an analysis of the RCF life-cycle and the number of people in each category has resulted in the type of statistical plan described in Table 1 together with some of the job titles in each category. In the U.S.A. over 2000 samples have been collected and analysed using the standard protocol and the results shared with the authorities. Over the next 3-5 years the U.S. PSP efforts will analyse samples/year and the CARE initiative in Europe will add another 720 samples annually. An analysis of the fibre counts has demonstrated that they are distributed log-normally and so are best described by geometric mean values. As the European programme only commenced in 1996 in this paper we report the historical data which was collected in Europe in a non-random way and compare this U.S. data in the same categories. In Figs 1 and 2 we show the geometric mean time-weighted average counts for various functional categories in both U.S. and Europe over the period The measurement of fibre levels cannot, in itself, lead to a reduction in airborne fibre levels, however levels have been dropping on both sides of the Atlantic, as is illustrated in Fig. 3. DISCUSSION Over 90% of all 8 h time-weighted averages so far measured have been below the

4 270 C. G.Burlcy etal. 1 -i Europe 2 USA Finishing Assembly Other Mix/form Prod. Aux Functional Category Fig. 1. The distribution of samples taken in the European ceramic fibre manufacturing and user industries as part of the CARE programme. The actual sites sampled are selected using a randomised sampling plan weighted by the quantity of fibre used. Thus accurate information on exposure to RCFs is obtained. 1 -i Europe YZ USA Install Finishing Assembly Mix/form Aux. Other Functional Category Fig. 2. Geometric mean fibre concentration by functional category at customer facilities, 1991 to 1996.

5 Refractory ceramic fibres 271 "E ^ 1.00 H 0.75 H Guidline value Europe o H Fig. 3. Historical trend of average workplace RCF exposures at European and U.S. manufacturing facilities weighted by distribution of workers in functional categories. guideline value of 1 f cc *. Exposures in the user industries are higher than those in manufacturing and in Europe higher than those in the U.S.A. Since the European counts have not been taken at random they may contain high values taken due to "problems" and thus may appear to drop when sufficient samples have been taken under the CARE programme. In nearly all areas exposures have been reduced substantially so that in the U.S.A. average levels in both manufacturing and user industries have fallen to about 0.2 f ml" 1 and in Europe to below 0.4 f ml" 1. A small proportion of all counts have been above the guideline value of 1 f ml" 1 but although taken with personal samplers these represent area values as workers under these conditions are protected through the use of personal protective equipment. Subsequently workplace controls have to be developed, this takes time and each situation has to be analysed and new equipment and technologies devised and implemented. Similarly the introduction of new work practices means that considerable time and effort must be expended in plant layout changes and/or employee training. The operation of this programme represents a much more thorough study of airborne fibre concentrations than that required by law in any country. The aim is to continue to reduce exposure to the lowest practical levels as a minimum the full operation of the "CARE" programme will lead to a reduction of airborne fibre concentrations in Europe to similar values to those found in the U.S.A. and, for similar operations, the differences between the manufacturing and user industries should also reduce.

6 272 C. G. Burley etal. Due to the present level of concern and the uncertainty regarding any possible MMMF health risks there is a potential for considerable over-regulation. However, tougher regulation does not necessarily mean safer practices and the RCF industry has voluntarily undertaken many of the initiatives that regulation might impose. Success in reducing exposure and the continuing human health surveillance results suggest that any potential risks from RCF exposure, whilst not to be underestimated, are remote enough to permit sufficient time to investigate these issues thoroughly prior to any action. The pressure to take quick, and possibly damaging, action has been reduced so that in the long term any regulations that may prove necessary can be both objective and well founded. REFERENCES Brown, R. C, Hoskins, J. A. and Glass, L. R. (1995) The in vivo biological activity of ceramic fibres. Ann. occup. Hyg. 39, Bunn, W. B., Bender, J. P., Hesterberg, T. W., Chase, G. R. and Konzen, J. L. (1993) Recent studies of man-made vitreous fibres. Chronic animal inhalation studies. J. occ. Med. 35, Davis, J., Addison, J., Bolton, R., Donaldson, K., Jones, A. and Wright, A. (1984) The pathogenic effects of fibrous ceramic aluminium silicate glass administered to rats by inhalation and peritoneal injection. In Biological Effects of Man-made Mineral Fibres (Edited by J.C. Wagner). World Health Organisation, Copenhagen. Glass, L. R., Brown, R. C. and Hoskins, J. A. (1995) Health effects of refractory ceramic fibres: scientific issues and policy considerations. Occ. Environ. Med. 52, IARC Monographs of the Evaluation of the Carcinogenic Risk of Chemicals to Humans; Man-made Mineral Fibres and Radon, Vol. 43, pp International Agency for Research on Cancer, Lyon, France. McClellan, R. O., Miller, F. J., Hesterberg, T. W., Warheit, D. B., Bunn, W. B., Kane, A. B., Lippmann, M., Mast, R. W., McConnell, E. E. and Reinhardt, C. F. (1992) Approaches to evaluating the toxicity and carcinogenicity of man-made fibers: summary of a workshop held November 11-13, 1991, Durham, North Carolina. Reg. Tox. Pharmacol. 16, Pott, F., Ziem, U., Reiffer, F., Huth, F., Ernst, H. and Mohr, U. (1987) Carcinogenicity studies of fibres, metal compounts and some other dusts in rats. Exptl. Path. 32, Smith, D., Oritz, L., Archuleta, R. and Johnson, N. (1987) Long term health effects in hamsters and rats exposed chronically to man-made vitreous fibres. Ann. occup. Hyg. 31,