Asbestos

Asbestos full information

Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, (1:20) thin fibrous crystals. The inhalation of asbestos fibers can cause serious illnesses, including malignant lung cancer, mesothelioma (a formerly rare cancer strongly associated with exposure to amphibole asbestos), and asbestosis (a type of pneumoconiosis). Long exposure to high concentrations of asbestos fibers is more likely to cause health problems.This is most common among the miners of asbestos, since they have the longest exposure to it. The European Union has banned all use of asbestos and extraction, manufacture and processing of asbestos products.

Asbestos became increasingly popular among manufacturers and builders in the late 19th century because of its sound absorption, average tensile strength, and its resistance to fire, heat, electrical and chemical damage. It was used in such applications as electrical insulation for hotplate wiring and in building insulation. When asbestos is used for its resistance to fire or heat, the fibers are often mixed with cement (resulting in fiber cement) or woven into fabric or mats. Commercial asbestos mining began in the Eastern Townships of Quebec, Canada and the world's largest asbestos mine is located in the town of Asbestos, Quebec.

Asbestos fibers potos

Asbestos fibers

Six minerals are defined by the United States Environmental Protection Agency as "asbestos" including those belonging to the serpentine class chrysotile and those belonging to the amphibole class amosite, crocidolite, tremolite, anthophyllite and actinolite. There is an important distinction to be made between serpentine and amphibole asbestos due to differences in their chemical composition and their degree of potency as a health hazard when inhaled. However asbestos and all commercial forms of asbestos (including chrysotile asbestos) are known to be human carcinogens based on sufficient evidence of carcinogenicity in humans.

Serpentine and Amphibole

White

Chrysotile, CAS No. 12001-29-5, is obtained from serpentinite rocks which are common throughout the world. Its idealized chemical formula is Mg3(Si2O5)(OH)4. Chrysotile fibers are curly as opposed to fibers from amosite, crocidolite, tremolite, actinolite, and anthophyllite which are needlelike. Chrysotile, along with other types of asbestos, has been banned in dozens of countries and is only allowed in the United States and Europe in very limited circumstances. Chrysotile has been used more than any other type and accounts for about 95% of the asbestos found in buildings in America. Applications where chrysotile might be used include the use of joint compound. It is more flexible than amphibole types of asbestos; it can be spun and woven into fabric. The most common use is within corrugated asbestos cement roof sheets typically used for outbuildings, warehouses and garages. It is also found as flat sheets used for ceilings and sometimes for walls and floors. Numerous other items have been made containing chrysotile including brake linings, cloth behind fuses (for fire protection), pipe insulation, floor tiles, and rope seals for boilers.

Amphibole

Brown

Amosite, CAS No. 12172-73-5, is a trade name for the amphiboles belonging to the cummingtonite-grunerite solid solution series, commonly from South Africa, named as an acronym from Asbestos Mines of South Africa. One formula given for amosite is Fe7Si8O22(OH)2. It is found most frequently as a fire retardant in thermal insulation products and ceiling tiles.

Blue

Crocidolite, CAS No. 12001-28-4 is an amphibole found primarily in southern Africa, but also in Australia. It is the fibrous form of the amphibole riebeckite. One formula given for crocidolite is Na2Fe2+3Fe3+2Si8O22(OH)2.

Crocidolite commonly occurs as soft friable fibers. Asbestiform amphibole may also occur as soft friable fibers but some varieties such as amosite are commonly straighter. All forms of asbestos are fibrillar in that they are composed of fibers with breadths less than 1 micrometer that occur in bundles and have very great widths. Asbestos with particularly fine fibers is also referred to as "amianthus". Amphiboles such as tremolite have a crystal structure containing strongly bonded ribbonlike silicate anion polymers that extend the width of the crystal. Serpentine (chrysotile) has a sheetlike silicate anion which is bowed and which rolls up like a carpet to form the fiber.

Other materials

Other regulated asbestos minerals, such as tremolite asbestos, CAS No. 77536-68-6, Ca2Mg5Si8O22(OH)2; actinolite asbestos, CAS No. 77536-66-4, Ca2(Mg, Fe)5(Si8O22)(OH)2; and anthophyllite asbestos, CAS No. 77536-67-5, (Mg, Fe)7Si8O22(OH)2; are less commonly used industrially but can still be found in a variety of construction materials and insulation materials and have been reported in the past to occur in a few consumer products.

Other natural and not currently regulated asbestiform minerals, such as richterite, Na(CaNa)(Mg, Fe++)5(Si8O22)(OH)2, and winchite, (CaNa)Mg4(Al, Fe3+)(Si8O22)(OH)2, may be found as a contaminant in products such as the vermiculite containing zonolite insulation manufactured by W.R. Grace and Company. These minerals are thought to be no less harmful than tremolite, amosite, or crocidolite, but since they are not regulated, they are referred to as "asbestiform" rather than asbestos although may still be related to diseases and hazardous.

Producing nations

In 2009, 2 million tonnes of asbestos were mined worldwide. Russia was the largest producer with about 50% world share followed by China (14%), Brazil (12.5%), Kazakhstan (10.5%) and Canada (9%).

Asbestos History

Asbestos use in human culture dates back at least 4,500 years, when evidence shows that inhabitants of the Lake Juojärvi region in East Finland strengthened earthenware pots and cooking utensils with the asbestos mineral anthophyllite. The word asbestos comes from the ancient Greek ἄσβεστος, meaning "unquenchable" or "inextinguishable". One of the first careful descriptions of the material is attributed to Theophrastus in his text On Stones, around 300 BC, although the naming of minerals was not very consistent at that time (the more consistent name of this material in both modern and ancient Greek is amiantos (undefiled, pure) whence the names of it in other languages like French amiante; the modern Greek word ἀσβεστος or ασβέστης stands consistently and solely for lime, not for the material known as asbestos in English). The term asbestos is traceable to Roman naturalist Pliny the Elder's manuscript Natural History, and his use of the term asbestinon, meaning "unquenchable". While Pliny is popularly attributed with recognising the detrimental effects of asbestos on slaves, examination of primary sources shows that this is not so. Charlemagne, the first Holy Roman Emperor (800-814), is said to have had a tablecloth made of asbestos.

According to Tabari, one of the curious items belonging to Khosrow II Parviz, the great Sassanian king (r. 531-579), was a napkin that he cleaned by simply throwing it into fire. This is believed to be made of asbestos. (This is also mentioned in The New Encyclopædia Britannica, vol. 6, 2003, page 843). Wealthy Persians, who bought asbestos imported over the Hindu Kush, amazed guests by cleaning the cloth by simply exposing it to fire. According to Biruni in his book of Gems, any cloths made of asbestos were called shostakeh. Some of the Persians believed the fiber was fur from an animal that lived in fire and died when exposed to water, hence the old mistaken myth that the salamander tolerated fire.

While traveling to Siberia, Marco Polo described being offered garments that could not burn. He was told that the wool was from the salamander, but did not accept this explanation. At last he was told that these garments were made from a mineral from the mountains, which contained threads just like wool.

Some archeologists believe that ancients made shrouds of asbestos, wherein they burned the bodies of their kings, in order to preserve only their ashes, and prevent their being mixed with those of wood or other combustible materials commonly used in funeral pyres. Others assert that the ancients used asbestos to make perpetual wicks for sepulchral or other lamps. In more recent centuries, asbestos was indeed used for this purpose. Although asbestos causes skin to itch upon contact, ancient literature indicates that it was prescribed for diseases of the skin, and particularly for the itch. It is possible that they used the term asbestos for soapstone, because the two terms have often been confused throughout history.