A mortality study of workers manufacturing friction materials with chrysotile asbestos.

This is a study of workers at a friction materials factory founded in 1898. Crocidolite was used only during two well defined periods before 1945. Apart from this, only chrysotile asbestos has been used. The mortality study dates from 1942 and extends to 1979. Over 99% of the population have been traced. Ten deaths from mesothelial tumours occurred. An analysis contrasting the observed number of deaths with those to be expected showed a significant excess of deaths from cancer of the lung and pleura in those employed before 1942. Among these deaths were seven from pleural mesothelioma. A case control study of the ten workers dying from pleural mesothelioma showed that all but two of these had definite exposure to crocidolite asbestos. Allowing for concomitant exposure to chrysotile asbestos among both cases and controls, the evidence of an association of the deaths from pleural mesothelioma with an exposure to crocidolite asbestos had a statistical significance level of 0.06. INTRODUCTION THIS mortality study has been carried out on the employees of a factory which has been producing friction materials since the turn of the century. Apart from two well defined periods when crocidolite asbestos was used for a specific order, only chrysotile asbestos has been used in the factory. The objectives of the study are, therefore, to establish the effects of exposure to chrysotile asbestos as used in this factory and to contrast this with the effects on subjects who were also exposed to crocidolite asbestos. The work programs were so arranged that none of the workers had a pure crocidolite exposure. It is also intended to establish dose-response relationships to chrysotile asbestos. The present communication deals with the first two objectives. After several years of experimentation on brake blocks and brake and clutch linings, the factory was founded by Herbert Frood in 1898. At that time cast iron, elm wood, leather, hemp, colliery wire and flax were all in use. Michelin in France had patented a brake block made of canvas laminated with rubber. However, gritty roads wore them away rapidly and at 7-10 shillings a pair they were reckoned to be expensive. Eventually Frood carried out experiments on cotton textile belting hardened and glazed with mineral oil, and patented the process in 1901. He continued to experiment with bonding materials and in patent of 1910 specified: '65 parts by weight of resin spirit, 25 parts rock bitumen, and 25 parts gum copal brought to a suitable condition by linseed oil with litharge or other drier added as required.' (FERODO, 1957). In 1910 he decided to experiment with woven asbestos, which proved to have far superior quality and had virtually supplanted cotton belting by 1920. No manufacture of cotton or