Man-made Mineral Fibres

Abstract

Insulation wools from glass fibres have been in production for over 40 years and similar products made from slag wool have been made since the 1880s. These products contain a significant proportion of fibres of respirable diameter. Continuous filaments for textile fibres have been made since the 1940s and contain only extremely small quantities of respirable fibres. The relatively high falling speed of large diameter fibres means that high gravimetric estimations may be associated with very small quantities of airborne respirable fibres in production plants. Fibres above 5 μm in diameter act as a primary irritant on the skin but continued exposure leads to hardening and a cessation of symptoms, sensitization does not occur. Prevalence studies of groups of workers exposed for lengthy periods to glass fibres in several countries produced evidence of the absence of pulmonary fibrosis, respiratory impairment and symptoms of bronchitis. Epidemiological studies have failed to show an excess risk of lung or other cancers. Reports of a small number of individual cases with respiratory disease and an exposure to glass fibres have not demonstrated a causal effect. Postmortem studies of workers with long-term exposure to glass fibres have shown no evidence of lung damage. Animal inhalation studies, in general, show that man-made mineral fibres elicit a macrophage response and the reaction is typical of a nuisance dust, significant fibrogenic reaction is not produced and carcinogenesis has not been demonstrated by inhalation. Injection of fibres into the pleura produces an incidence of tumours related to the number, diameter and length of fibres. The order of diameter of biological significance is believed to be between 0.5 and 1 μm in diameter. Such effects have not been observed in man and are obtained with all durable fibres, asbestos being the only substance for which a similar effect is known to occur in humans. Cell culture work suggests the mechanism of tumorigenesis differs from that of most carcinogens and may resemble the Oppenheimer effect.