In 1991 the US Occupational Safety and Health Administration decided that glass fibre products should be labelled as a potential cancer hazard.(1) The decision followed studies of glass fibre workers that showed an increased risk of lung cancer.
Glass wool products have been manufactured for about 60 years during which animal experiments seemed reassuring. In the 1950s, experiments with rats, guinea pigs, rabbits and monkeys produced no lung damage when the animals were forced to breathe the fibres.(2) And an analysis of further tests conducted during the 1980s noted that "An increase in lung tumours or mesothelioma has not been observed following long-term inhalation studies in several animal species including rats, hamsters, guinea pigs, mice, monkeys, and baboons exposed to glass fibres, glass wool or mineral wool."(3)
Ironically, experiments in which rats did develop cancer have been dismissed as unlikely to have any relevance to the human condition. This is because the glass fibres were artificially implanted into the tissue membrane lining the animal's lung, whereas in people the usual means of exposure is through breathing. Furthermore, it is well known that rats are especially prone to cancer when solid substances are surgically implanted into their bodies.(2) In his book Occupational Lung Disorders, Raymond Parkes concludes that "the production of malignant tumours in animals by direct implantation experiments is unlikely to have any relevance to human exposure."
I ) Letter from G.F.Scannell, Assistant Secretary for Occupational Safety and Health, Washington DC, to Richard Munson, Chairman of Victims of Fibreglass (May 6,1991); The Guardian, July 20, 1991.
2) Reported in R.Parkes, Occupational Lung Disorders (Butterworths, 1982).
3) C.S.Wheeler, Toxicology & Industrial Health, 1990, vol.6, 293-307.
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