Document evn0rKZ0KeY2aJ7dEew3jZYKp

cations rcssurc izalion. osiic is :nt acid in this Asbestos and asbcstosb 5 Very broadly it can be said that current friction materials, whether they be disc brake pads, passenger car and commercial vehicle brake linings or dutch facings, contain SO per cent chrysolite asbestos. The new trends of development, particularly in the fields of disc brake pads and commercial vehicle brake finings* indicate that the percentage of asbestos included in the mix is likely to dedine. Some new materials now contain approximately 40 per cent asbestos, and newer mixes can be foreseen with an even lower percentage, probably down to a minimum of 30 per cent. The pads for disc brakes require less asbestos fibre than conventional drum brake linings. It is estimated that more and more passenger ears produced in the U.K.. will in future be equipped with disc brakes, particularly on the front wheels. THE BIOLOGICAL EFFECTS OF ASBESTOS The variation existing in the biological effects of the different types of asbestos is the .subject of considerable interest and research, and the extent to which the physical and chemical characteristics of the asbestos itself influence biological effects is being investigated. The role of trace dements and contaminants associated with the fibres has also to be considered. The chief biological effects of asbestos are confined to the lung and the pleura, or lining or the lung and ehesi cavity, and to the peritoneum, or lining of the abdominal cavity. A few cases of skin corns have occured in asbestos workers, but these are becoming much less common. All types or asbestos, if inhaled in fairly high concentrations over a considerable period of time, may cause fibrosis of the lungs. This disease, called nsbestosis, con sists of thickening of the lung membranes with resultant stiffening of the tissues and interference with oxygen uptake. The interference with gas transfer is the reason for the shortness of breath which causes the disability associated with asbestosis. The amount of exposure required to produce fibrosis of the pleura, with or without calcium deposition in the scars, is more debatable. It may be that shorter, less concentrated exposures, particular))' in youth, leave this mark upon the pleura. In any event this particular effect of asbestos inhalation causes little or no disability in itself Exposure to asbestos may lead to further complications, e.g., heart failure, cancer or the lung, or, rarely, to malignant changes in the pleura or peritoneum, known as mesothelioma. Cancer ofThe lung 1m -teen -shown to -be more common tn -asbestos workers who smoke, just as it is in the general population. Mesotheliomas arc very uncommon throughout the world, but in some areas they have been associated more frequently with exposure to croeidolite than to chrysolite, amositc or anthophyliiic. The reasons for this are at present obscure, but arc being sought intensively by investigators in many different countries.