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White asbestos is classified by the International Agency for Research on Cancer, on behalf of the World Health Organisation, as a category 1 carcinogen hazardous by inhalation. The most recent and comprehensive study carried out on the relative risks of asbestos "The Quantitative Risks of Mesothelioma and Lung Cancer in Relation to Asbestos Exposure" suggests there is a real risk of cancer from white asbestos (1 in 5,000) at levels of exposure realistically experienced by maintenance workers. The quantification of risk at these levels of exposure is however highly uncertain. The same paper implies the arguable range of risk runs from a quarter to seven times the central estimate.