The name is derived for its historical use in lamp wicks; the resistance of asbestos to fire has long been exploited for a variety of purposes. Asbestos was used in fabrics such as Egyptian burial cloths and Charlemagne's tablecloth (which according to legend, he threw in a fire to clean). Asbestos occurs naturally in many forms (see below); it is mined from metamorphic rocks.
When asbestos is used for its resistance to fire or heat, the fibers are often mixed with cement or woven into fabric or mats. Asbestos is used in brake shoes and gaskets for its heat resistance, and in the past was used on electric oven and hotplate wiring for its electrical insulation at elevated temperature, and in buildings for its flame-retardant and insulating properties, tensile strength, flexibility, and resistance to chemicals. The inhalation of asbestos fibers can cause a number of serious illnesses, including mesothelioma and cancer. Since the mid 1980s, many uses of asbestos are banned in multiple countries.
Types of asbestos and associated fibres
Chrysotile asbestos
Asbestos fibersSix minerals are defined as "asbestos" including, chrysotile, amosite, crocidolite, tremolite, anthophyllite and actinolite.
"White" asbestos
Chrysotile, CAS No. 12001-29-5, is obtained from serpentine rocks which is common throughout the world. The rocks are called serpentine because their fibers curl; 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 is 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. Chrysotile, like all other forms of industrial asbestos, has produced tumors in animals. Mesotheliomas have been observed in people who were occupationally exposed to chrysotile, family members of the occupationally exposed, and residents who lived close to asbestos factories and mines.
"Brown" asbestos
Amosite, CAS No. 12172-73-5, is a trade name for the amphiboles belonging to the Cummingtonite - Grunerite solid solution series, commonly from 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. This type of asbestos, like all asbestos, is very hazardous.
"Blue" asbestos
Crocidolite, CAS No. 12001-28-4 is an amphibole from Africa and Australia. It is the fibrous form of the amphibole riebeckite. Blue asbestos is commonly thought of as the most dangerous type of asbestos (see above and below). One formula given for Crocidolite is Na2Fe2+3Fe3+2Si8O22(OH)2. This type of asbestos is very hazardous.
Notes: chrysotile 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 widths less than 1 micrometre that occur in bundles and have very long lengths. Asbestos with particularly fine fibers is also referred to as "amianthus". Amphiboles such as tremolite have a sheetlike crystalline structure. Serpentine (chrysotile) has a stringlike crystalline structure.(Inorganic Chemistry, E. de Barry Barnett and C. L. Wilson). Tremolite often comtaminates chrysotile asbestos, thus creating an additional hazard.
Other asbestos
Other regulated asbestos minerals, such as tremolite asbestos, CAS No. 77536-68-6, Ca2Mg5Si8O22(OH)2; actinolite asbestos (or smaragdite), CAS No. 77536-66-4, Ca2(Mg, Fe)5Si8O22(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 reltated to diseases and hazardous.
In 1989 the United States Environmental Protection Agency (EPA) issued the Asbestos Ban and Phase Out Rule which was subsequently overturned in the case of Corrosion Proof Fittings v. U.S. Environmental Protection Agency, 1991. This ruling leaves many consumer products that can still legally contain trace amounts of asbestos. For a clarification of products which legally contain asbestos visit the EPA's clarification statement.
Production trends
Asbestos output in 2005In 2005, the world mined 2,200,000 tons of asbestos, Russia was the largest producer with about 40% world share followed by China and Kazakhstan, reports the British Geological Survey.
Uses
Historic usage
Asbestos was named by the ancient Greeks who also recognized certain hazards of the material. The Greek geographer Strabo and the Roman naturalist Pliny the Elder noted that the material damaged lungs of slaves who wove it into cloth. Charlemagne, the first Holy Roman Emperor, had a tablecloth made of asbestos. Wealthy Persians, who bought asbestos imported over the Hindu Kush, amazed guests by cleaning the cloth simply by exposing it to fire. The Persians believed the fiber was fur from an animal that lived in fire and died when exposed to water. 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 alumen plumosum, because the two terms have often been confused throughout history.
Asbestos became more widespread during the industrial revolution, in the 1860's it was being used as insulation in the US and Canada. Development of the first commercial asbestos mine began in 1879 in the Appalachian foothills of Quebec. By the mid 20th century uses included fire retardant coatings, concrete, bricks, pipes and fireplace cement, heat, fire, and acid resistant gaskets, pipe insulation, ceiling insulation, fireproof drywall, flooring, roofing, lawn furniture, and drywall joint compound.
Approximately 100,000 people have or will die from asbestos exposure related to ship building. In Hampton Roads, a shipbuilding town, mesothelioma occurance is seven times the national rate. Thousands of metric tons of asbestos were used in WWII ships to wrap the pipes, line the boilers, and cover engine and turbine parts. There were approximately 4.3 million shipyard workers during WWII, for every thousand workers about 14 died of mesothelioma and an unknown number died from asbestosis.
Asbestos fibers were once used in automobile brake pads and shoes. Since the mid-1990s, a majority of brake pads, new or replacement, have been manufactured instead with Aramid fiber (Twaron or Kevlar) linings (the same material used in bulletproof vests).
Kent, the first filtered cigarette on the market, used crocidolite asbestos in its "Micronite" filter from 1952 to 1956.
The first documented death related to asbestos was in 1906. In the early 1900's researchers began to notice a large number of early deaths and lung problems in asbestos mining towns. The first diagnosis of asbestosis was made in England in 1924. England protected asbestos workers about ten years faster than the US, by the 1930s England regulated ventilation and made asbestos an excusable work related disease. The term mesothelioma was not used in medical literature until 1931, and wasn't associated with asbestos until sometime in the 1940's.
The United States government and asbestos industry have been criticized for not acting fast enough to inform the public of dangers, and reduce public exposure. In the late 1970's court documents proved that asbestos industry officials knew of asbestos dangers and tried to conceal them.
In Japan, particularly after World War II, asbestos was used in the manufacture of ammonium sulfate for purposes of rice production, sprayed upon the ceilings, iron skeletons, and walls of railroad cars and buildings (during the 1960s), and used for energy efficiency reasons as well. Production of asbestos in Japan peaked in 1974 and went through ups and downs until about 1990, when production began to drop severely.
Modern usage
Serpentine group
In the United States, chrysotile has been the most commonly used type of asbestos. Chrysotile is often present in a wide variety of materials, including :
joint compound
mud and texture coats
vinyl floor tiles, sheeting, adhesives
roofing tars, felts, siding, and shingles
"transite" panels, siding, countertops, and pipes
fireproofing
caulk
gaskets
brake pads and shoes
clutch plates
stage curtains
fire blankets
interior fire doors
fireproof clothing for firefighters
thermal pipe insulation
In the European Union and Australia it has recently been banned as a potential health hazard and is not used at all. Japan is moving in the same direction, but more slowly. Revelations that hundreds of workers had died in Japan over the previous few decades from diseases related to asbestos sparked a scandal in mid-2005. Tokyo had, in 1971, ordered companies handling asbestos to install ventilators and check health on a regular basis; however, the Japanese government did not ban crocidolite and amosite until 1995, and a full-fledged ban on asbestos was implemented in October 2004.
Amphibole group
Amosite and crocidolite were formally used in many products until the early 1980s. The use of all types of asbestos in the amphibole group was banned (in much of the Western world) by the mid-1980s, and by Japan in 1995. These products were mainly:
Low density insulation board and ceiling tiles
asbestos-cement sheets and pipes for construction, casing for water and electrical/telecommunication services
thermal and chemical insulation (i.e., fire rated doors, limpet spray, lagging and gaskets)
Health issues
Police officer wearing protective filter mask against possible asbestos inhalation
Asbestos Warning Sign at Bauer Elementary Miamisburg, Ohio June 2007Health concern associated with asbestos began in the 1970s soon after Dr. Irving Selikoff, of Mt. Sinai School of Medicine, found that some workers, occupationally exposed to certain amphibole (non-serpentine) type asbestos fibers, were at increased risk of lung disease. EWG Action Fund estimates that in the United States, about 10,000 people die each year of asbestos-related diseases, such as mesothelioma, asbestosis, lung cancer, and gastrointestinal cancer.
Asbestos as a contaminant
Most respirable asbestos fibers are invisible to the unaided human eye because their size is about 3.0-20.0 µm in length and can be as thin as 0.01 µm. Human hair ranges in size from 17 to 181 µm in width. Fibers ultimately form because when these minerals originally cooled and crystallized, they formed by the polymeric molecules lining up parallel with each other and forming oriented crystal lattices. These crystals thus have three cleavage planes, just as other minerals and gemstones have. But in their case, there are two cleavage planes that are much weaker than the third direction. When sufficient force is applied, they tend to break along their weakest directions, resulting in a linear fragmentation pattern and hence a fibrous form. This fracture process can keep occurring and one larger asbestos fiber can ultimately become the source of hundreds of much thinner and smaller fibers.
As asbestos fibers get smaller and lighter, the more easily they become airborne and human respiratory exposures can result. Fibers will eventually settle but may be re-suspended by air currents or other movement.
Friability of a product containing asbestos means that it is so soft and weak in structure that it can be broken with simple finger crushing pressure. Friable materials are of the most initial concern due to their ease of damage. The forces or conditions of usage that come into intimate contact with most non-friable materials containing asbestos are substantially higher than finger pressure.
Naturally occurring asbestos
Asbestos from natural geologic deposits is known as "Naturally Occurring Asbestos"(NOA). Health risks associated with exposure to NOA are not yet fully understood, and current federal regulations do not address exposure from NOA. Many populated areas are in proximity to shallow, natural deposits which occur in 50 of 58 California counties and in 19 other U.S. states. In one study, data was collected from 3,000 mesothelioma patients in California and 890 men with prostate cancer, a malignancy not known to be related to asbestos. The study found a correlation between the incidence of mesotheliomas and the distance a patient lived from known deposits of rock likely to include asbestos, the correlation was not present when the incidence of prostate cancer was compared with the same distances. According to the study, risk of mesothelioma declined by 6 percent for every 10 kilometers that an individual had lived from a likely asbestos source.
Portions of El Dorado county are known to contain natural asbestos formations near the surface. The USGS studied amphiboles in rock and soil in the area in response to an EPA sampling study and subsequent criticism of the EPA study. The study found that many amphibole particles in the area meet the counting rule criteria used by the EPA for chemical and morphological limits, but do not meet morphological requirements for commercial-grade-asbestos. The executive summary pointed out that even particles that do not meet requirements for commercial-grade-asbestos may be a health threat and suggested a collaborative research effort to assess health risks associated with "Naturally Occurring Asbestos".
Large portions of Fairfax County, Virginia were also found to be underlain with tremolite. The county monitored air quality at construction sites, controlled soil taken from affected areas, and required freshly developed sites to lay 6 inches of clean, stable material over the ground.
Asbestos in the environment
Abestos is in the air we breathe and some of the water we drink, including water from natural sources. Studies have shown that members of the general (nonoccupationally exposed) population have tens of thousands to hundreds of thousands of asbestos fibers in each gram of dry lung tissue, which translates into millions of fibers and tens of thousands of asbestos bodies in every person's lungs.
The EPA has proposed a concentration limit of 7 million fibers per liter of drinking water for long fibers (lengths greater than or equal to 5 µm). OSHA (Occupational Safety and Health Administration) has set limits of 100,000 fibers with lengths greater than or equal to 5 µm per cubic meter of workplace air for 8-hour shifts and 40-hour work weeks.
Asbestos construction in developing countries
Countries like India and China 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. Eternit Everest, Hyderabad Industries and RamCo are some of the major asbestos products manufacturers in India.
Cutting these sheets to size and drilling for 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.
Other asbestos-related diseases
asbestos warts – caused when the sharp fibers lodge in the skin and are overgrown causing benign callus-like growths.
pleural plaques – discrete fibrous or partially calcified thickened area which can be seen on X-rays of individuals exposed to asbestos. They do not become malignant or cause other lung impairment.
diffuse pleural thickening – similar to above and can sometimes be associated with asbestosis. Usually no symptoms shown but if extensive can cause lung impairment.
Litigation
Asbestos litigation is the longest, most expensive mass tort in U.S. history, involving more than 6,000 defendants and 600,000 claimants. Current trends indicate that the rate at which people are diagnosed with the disease will likely increase through the next decade. Analysts have estimated that the total costs of asbestos litigation in the USA alone is over $250 billion. Due to the prevalence of asbestos, it is normally part of the scope of a Phase I Environmental Site Assessment to inspect for potential asbestos in a building which is being sold.
The volume of the asbestos liability has alarmed the manufacturers and insurance industry. The amounts and method of allocating compensation have been the source of many court cases, and government attempts at resolution of existing and future cases.
Critics of safety regulations
Asbestos regulation critics include the controversial Junkscience.com author and Fox News columnist Steve Milloy and the asbestos industry. Critics sometimes argue that increased regulation does more harm than good and that replacements to asbestos are inferior. An example is the suggestion by Dixy Lee Ray and others that the shuttle Challenger exploded because the maker of O-ring putty was pressured by the EPA into ceasing production of asbestos-laden putty.[ However, scientists point out that the putty used in Challenger's final flight did contain asbestos, and failures in the putty were not responsible for the failure of the O-ring that led to loss of the shuttle.
Asbestos was used in the first 40 floors of the World Trade Towers and ended up contaminating the air around lower Manhattan after the towers collapsed. Steven Milloy suggests that the World Trade Center towers could still be standing or at least would have stood for longer had a 1971 ban not stopped the completion of the asbestos coating above the 64th floor. This was not mentioned in the National Institute of Standards and Technology's report on the Towers' collapse. Insulation that replaced asbestos is believed to have equivalent fire resistance, and any sort of sprayed-on insulation, including asbestos-based material, would have been removed in large areas by the impact of the planes and subsequent explosion.
Substitutes for asbestos in construction
Fiberglass insulation was invented in 1938 and is now the most commonly used type of insulation material.
Many companies that produced asbestos-cement products that were reinforced with asbestos fibres have developed products incorporating organic fibres. One such product was known as Eternit and another Everite now use Nutec fibres which consist of organic fibres, portland cement and silica.
Another potential fiber is Polybenzimidazole or PBI fiber. Polybenzimidazole is a synthetic fiber with no melting point that also does not ignite. Due to its exceptional thermal and chemical stability, it is often used by fire departments and space agencies.
aspestos
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