Document ZJyQ88QbZRv2xGEvQVe1L0BmJ

115 The original recommendation by BOHS (1969) stated; *'Such early clinical signs will be less than 1% for an accumulated exposure of 100 fibre years per cm"**'. Conversion of this recommendation into a standard of 2 f/rnl does not fully comply wit); the BOKS recommendation which was based upon accumulated exposure. Berry (1973) commented critically on the 2 fibre/ml limit; it has mainly been based upon one study in workers of an asbestos-textile factory who worked for at least 10 years; workers who had already left, may have been more susceptible. The 1\ limit has a 95t range of confidence up to about 3%; so 99% of workers would be protected with an accumulated dost* <51 fibre-years, and more than 97% with a dose of <100 fibre-years. The N10SH criteria document (1972) sums up.the following con^trolnts in applicability of icseerch data in t)ie dove)opr*nt of recommendations: a) - few epidemiological data or clinical reports with supporting evi dence arc available; b) - available environmcntal data on practically all studies were collec ted only over the last few years and/or collected by other techniques end expressed in terms other than fibres/ml; c) - envjronmcntal samples were expressly collected in many cases for control purposes and not for research; d) - there is a lack of data to define with any degree of precision the threshold of development of neoplasms resulting from exposure to asbestos and the relationship of the*latent period between exposure and development of neoplasms. The approach which led to the permissible limit of 2 fibres/ml is based upon an epidemiological study; one started fibre counts as a measure of exposure, because in animal experiments such an exposure had induced asbestosis. However, there is a very long way to go from such experiments on animal health regarding occupational health (ashestosis) t> public health (malignancies). The U.K. standard for chrysotilc was based uj<n epidemiological evidt-C'.c. but the standard for crocidolite was purely based upon an administrative decision, and not on research data. According to Weiss (1975) Gil lam of N30SH has found that the lung cancer risk among hard rock miners exposed to an esbcstiforDi material, mostly amosite, was three times that expected, despite the fact that fibre counts (>S pm) wen.* well below the 1976 standard of 2 fibrcs/ml; most of the fibres were short; . however arsenic was considered a possible factor. *001 0808 PROTYI ippn PV Prpr>