Asbestos

 

 

Asbestos is a term used to refer to six naturally occurring silicate minerals. All are composed of long and thin fibrous crystals, each fiber being composed of many microscopic 'fibrils' that can be released into the atmosphere by abrasion and other processes. Asbestos is an excellent electrical insulator and is highly resistant to heat, so for many years it was used as a building material. However, it is a well known health hazard, and today its use as a building material is banned in many countries. Inhalation of asbestos fibres can lead to various serious lung conditions, including asbestosis and cancer.
People have used asbestos for thousands of years to create flexible objects, such as napkins, that resist fire. In the modern era, companies began producing asbestos consumer goods on an industrial scale. Now people recognize the health hazard that asbestos dust poses, and it is banned or strictly regulated around the world.
Industrial-scale mining began in the Thetford hills, Quebec, from the 1870s. Sir William Edmond Logan was the first to notice the large deposits of chrysotile in the hills in his capacity as head of Geological Survey of Canada. Samples of the minerals from here were displayed in London, and excited much interest. With the opening up of the Quebec Central Railway in 1876, mining entrepreneurs such as Andrew Stuart Johnson established the asbestos industry in the province.[28 The 50 ton output of the mines in 1878 rose to over 10,000 tons in the 1890s with the adoption of machine technologies and expanded production. For a long time, the world's largest asbestos mine was the Jeffrey mine in the town of Asbestos, Quebec.
In the early 1900s, researchers began to notice a large number of early deaths and lung problems in asbestos-mining towns. The first such study was conducted by H. Montague Murray at the Charing Cross Hospital, London, in 1900, in which a postmortem investigation of a young man who had died from pulmonary fibrosis after having worked for 14 years in an asbestos textile factory, discovered asbestos traces in the victim's lungs. Adelaide Anderson, the Inspector of Factories in Britain, included asbestos in a list of harmful industrial substances in 1902. Similar investigations were conducted in France and Italy, in 1906 and 1908, respectively.
Some countries, such as India, Indonesia, China, Russia and Brazil, have continued widespread use of asbestos. The most common is corrugated asbestos-cement sheets or "A/C sheets" for roofing and for side walls. Millions of homes, factories, schools or sheds and shelters continue to use asbestos. Cutting these sheets to size and drilling holes to receive 'J' bolts to help secure the sheets to roof framing is done on-site. There has been no significant change in production and use of A/C sheets in developing countries following the widespread restrictions in developed nations.
One vermiculite mine operated by W. R. Grace and Company in Libby, Montana exposed workers and community residents to danger by mining vermiculite contaminated with asbestos, typically richterite, winchite, actinolite or tremolite. Vermiculite contaminated with asbestos from the Libby mine was used as insulation in residential and commercial buildings through Canada and the United States. W. R. Grace and Company's loose-fill vermiculite was marketed as Zonolite but was also used in sprayed-on products such as Monokote.
The mining company, R T Vanderbilt Co of Gouverneur, New York, which supplied the talc to the crayon makers, states that "to the best of our knowledge and belief" there is no asbestos in its talc. However media reports claim that the United States Mine Safety and Health Administration (MSHA) had found asbestos in four talc samples tested in 2000. The Assistant Secretary for Mine Safety and Health subsequently wrote to the news reporter, stating that "In fact, the abbreviation ND (non-detect) in the laboratory report indicates no asbestos fibers actually were found in the samples." Multiple studies by mineral chemists, cell biologists, and toxicologists between 1970 and 2000 found neither samples of asbestos in talc products nor symptoms of asbestos exposure among workers dealing with talc, but more recent work has rejected these conclusions in favor of "same as" asbestos risk.