What is asbestos?
Asbestos refers to a group of magnesium silicates which have both a crystalline and a fibrous structure; the six most common are actinolite, chrysotile, tremolite, anthophyllite, crocidolite and amosite. The modern English word asbestos comes from the ancient Greek word asbestos, meaning unquenchable.’
Asbestos is extremely resistant to heat and flame and is an excellent insulator. Its fibers are so light that they become airborne, and so flexible that they can be spun and woven into fabric. The fibers occur in two basic forms: amphiboles, which are straight needle-like fibers, and serpentine asbestos, whose fibers are curled and more flexible. Until recently, studies suggested that only amphiboles caused cancer. More recent research has established that Chrysotile fibers, which are serpentine, can also cause mesothelioma. Tremolite and Crocidolite, straight fibers, are considered more hazardous.
Major asbestos deposits are found in Russia, China, Canada, Brazil, Kazakhistan and Zimbabwe, and smaller outcrops are found in North America and southern Europe.
Asbestos in the ancient world
Humans have known about and used asbestos for 4000 years. The ancient Egyptians, Greeks, and Romans were familiar with asbestos, and regarded its resistance to flame was as akin to magic. They reserved asbestos for use in religious purposes, such as wicks for the sacred lamps used by the vestal virgins, priestesses of the goddess Vesta, protector of Rome. Asbestos was also used for cremation robes for emperors and other nobles. The Greek geographer Strabo and Pliny the Elder, a Roman historian and naturalist, both wrote about asbestos. Each of them noted that slaves who worked with the material frequently developed a sickness of the lungs.
The explorer Marco Polo traveled to Siberia, and later wrote of a cloth he was shown there that could be thrown into a fire and would not burn nor be consumed. His guides told him that it was woven from a mineral mined in the local mountains.
In the Middle Ages the emperor Charlemagne was believed to have magical powers. He convinced a group of hostile warlords of his powers when he pulled tablecloth from the table, threw it into the fireplace, and then pulled it out, unburned. The cloth was woven of asbestos.
Naturally occurring asbestosMap showing major asbestos deposits
Modern industrial uses of asbestos
Asbestos has been used in industrial applications since about 1880. More than 3000 products using asbestos have been identified. The list of asbestos products include fire resistant insulation, gas masks, water and sewage pipes, cement building materials, reinforcement in asbestos-cement products, brakes and clutches, sprayed fire-proofing products, floor tiles and coverings. Boilers and pipes in factories, steel plants, and power stations, as well as in hospitals, schools, and homes were insulated with asbestos products. Railroads and shipbuilding facilities have relied on asbestos as a primary insulator. Building contractors have used asbestos in industrial and domestic construction for thermal and acoustic insulation, protection from moisture and condensation and of course for fireproofing.
How asbestos causes cancer
Asbestos minerals consist of fibers that are easily separable. Individual fibers are extremely small and fine, light enough to be carried in the air.
In the course of mining, manufacturing and installing products using asbestos, fibers are dislodged and become airborne. Workers have described mining and factory environments where the air was white with asbestos dust, and their clothes and hair were covered with the fine white fibers. Asbestos workers cannot avoid inhaling the airborne fibers, especially when ventilation is poor, and protective apparatus is insufficient or lacking.
Most inhaled fibers are cleared from the lungs within hours of inhalation. Coughing carries them to the throat in a layer of mucus, where they are either spit out, or swallowed, and make their way out of the body.
Inhaled asbestos fibers that are not expelled stay in the lungs, and progress into the alveoli, the tiny pockets within the lung where oxygen passes into the bloodstream. Once asbestos fibers reach the alveoli, they may remain for years, even the rest of a person's life. Amphibole asbestos fibers tend to remain in the lung the longest. Asbestos fibers tend to move toward the lower regions of the lungs. In autopsies, most asbestos disease of the lungs is found in the bottom lobes of the lungs and on the surface of the diaphragm, the large muscle that moves the lungs in breathing, which sits just under the lungs.
Asbestos fibers that remain embedded in the lungs can cause mesothelioma, lung cancer, and asbestosis, three serious and potentially fatal diseases. All of these diseases develop very slowly. The first symptoms of mesothelioma may not show up for 15, sometimes for as long as 40 years after the victim's exposure to asbestos. By the time symptoms are troublesome enough for a victim to seek medical attention, the mesothelioma may have progressed so far that the life expectancy will be measured in months.