Exposure and Respiratory Health of Workers in the Australian Refractory Ceramic Fibre Production Industry

Abstract

Refractory ceramic fibre (RFC) is a subset of synthetic or vitreous mineral fibres (SMF) being composed of aluminium and silicon oxides. They have a high melting point and hence provide insulation application at temperatures up to 1400°C. To achieve the insulation properties, fibre is manufactured with nominal diameters of around 3-4 micrometers which is finer than other major commercial SMF types. In most instances the produce is manufactured without binder which with its finer fibre diameters results during handling in the generation of larger quantities of respirable fibres than does other commercial SMF. In addition the chemical composition of RCF makes it more durable in biological systems than most other commercial SMF. These factors of diameter, dose and biological durability have been recognised from experiences in asbestos and other natural and synthetic mineral fibres as major influences on fibre toxicity and carcinogenicity (Glass et al., 1995). In 1988 as a result of increasing concern within the community about the possible health effects from exposure to SMF the National Occupational Health and Safety Commission established a Technical Working Group to investigate typical levels of exposure in manufacturing and user industries and possible health effects and, based on available information, recommend exposure standards and safe working practices. In examining data derived from the Australian RCF industry, the Technical Group found upper respiratory tract irritation at concentrations above 1 fml 1 and for employees under medical surveillance (cross-sectional studies) no evidence of lung fibrosis. In terms of evidence for cancer, no suitable epidemiological studies were found anywhere for determining lung cancer or mesothelioma risk although data from the Australian Mesothelioma Surveillance Program indicated no cases associated with the manufacture of SMF (Worksafe, 1989). As part of its recommendations the Technical Group prepared a standardised membrane filter method for monitoring airborne SMF fibres and a gravimetric method for inspirable dust. Through the tripartite and public comment processes the Commission declared a national exposure standard of 0.5 fml 1 for all types of SMF and a secondary standard of 2 mgm~ 3 of inspirable dust to protect against