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asbestos

  (ăs-bĕs'təs, ăz-) pronunciation
n.

Either of two incombustible, chemical-resistant, fibrous mineral forms of impure magnesium silicate, used for fireproofing, electrical insulation, building materials, brake linings, and chemical filters.

adj.

Of, made of, or containing one or the other of these two mineral forms.

[Middle English asbestus, from Latin asbestos, mineral or gem, from Greek, mineral or gem, unslaked lime, from asbestos, unquenchable : a-, not; see a–1 + sbennunai, sbes-, to quench.]

asbestine as·bes'tine (-tĭn) or as·bes'tic (-tĭk) adj.
 
 
How Products are Made: How is asbestos made?

Background

Asbestos is a general name that applies to several types of fibrous silicate minerals. Historically, asbestos is best known for its resistance to flame and its ability to be woven into cloth. Because of these properties, it was used to make fireproof stage curtains for theaters, as well as heat-resistant clothing for metal workers and firefighters. More modern applications of asbestos take advantage of its chemical resistance and the reinforcing properties of its fibers to produce asbestos-reinforced cement products including pipes, sheets, and shingles used in building construction. Asbestos is also used as insulation for rocket engines on the space shuttle and as a component in the electrolytic cells that make oxygen on submerged nuclear submarines. Much of the chlorine for bleach, cleansers, and disinfectants is produced using asbestos products.

The earliest known use of asbestos was in about 2500 B.C. in what is now Finland, where asbestos fibers were mixed with clay to form stronger ceramic utensils and pots. The first written reference to asbestos came from Greece in about 300 B.C. when Theophrastus, one of Aristotle's students, wrote a book entitled On Stones. In his book, he mentioned an unnamed mineral substance, which looked like rotten wood, yet was not consumed when doused with oil and ignited. The Greeks used it to make lamp wicks and other fireproof items. When the Roman naturalist and statesman Pliny the Elder wrote his comprehensive Natural History in about 60 A.D., he described this fire-proof mineral and gave it the name asbestinon, meaning unquenchable, from which we get the English word asbestos.

Although the fireproof qualities of asbestos continued to fascinate the scientific community for hundreds of years, it wasn't until the 1800s that asbestos found many commercial uses. The first United States patent for an asbestos product was issued in 1828 for a lining material used in steam engines. In 1868 Henry Ward Johns of the United States patented a fireproof roofing material made of burlap and paper laminated together with a mixture of tar and asbestos fibers. It became an immediate success. Large-scale mining of asbestos deposits near Quebec, Canada, began in 1878 and spurred the development of other commercial uses. By 1900 asbestos was being used to make gaskets, fireproof safes, bearings, electrical wiring insulation, building materials, and even filters to strain fruit juices.

Technological developments in the early 1900s resulted in even more uses for asbestos. Many of the early plastic materials relied on asbestos fibers for reinforcement and heat resistance. Vinyl-asbestos tile became one of the most commonly used floor coverings and remained in use well into the 1960s. Automobile brake linings and clutch facings also used large amounts of asbestos, as did a multitude of building materials. After World War II, the use of asbestos in products continued to expand. Heart surgeons used asbestos thread to close incisions, Christmas trees were decorated with asbestos artificial snow, and a brand of toothpaste was marketed using asbestos fibers as an abrasive.

The widespread use of asbestos was not without a dark side, however. Health problems associated with exposure to airborne asbestos particles had been noted since the early 1900s, and resulted in the passage of the Asbestos Industry Regulations of 1931 in England. By the mid-1960s, health problems began to surface among shipyard workers who handled asbestos insulation during World War II. In the United States, the problem reached the crisis stage by the 1970s, forcing the Environmental Protection Agency (EPA) to place severe restrictions on the use of asbestos. Although the EPA lifted the ban for certain kinds of asbestos in 1991, the public's faith had been severely shaken, and most manufacturers had voluntarily removed asbestos from their products. As a result, asbestos usage in the United States fell from about 880,000 tons/yr (800,000 metric tons/yr) in 1973 to less than 44,000 tons/yr (40,000 metric tons/yr) in 1997.

In other countries, asbestos products are still widely used, especially in the construction industry. Worldwide usage of asbestos in 1997 was estimated at about 2.0 million tons/yr (1.8 million metric tons/yr). Most of this asbestos is used to make asbestos-reinforced concrete products, where the asbestos fibers are locked within the concrete.

Asbestos mining operations are found in 21 countries. The leading producers of asbestos are Russia (formerly the USSR), Canada, Brazil, Zimbabwe, China, and South Africa. Smaller deposits are found in the United States and several other countries.

Raw Materials

There are six types of asbestos: actinolite, amosite, anthophyllite, crocidolite, tremolite, and chrysolite. The first five types are known as amphiboles. They are characterized by having very strong and stiff fibers, which makes them a serious health hazard. Amphibolic asbestos fibers can penetrate body tissue, especially in the lungs, and eventually cause tumors to develop. The sixth type of asbestos, chrysotile, is known as a serpentine. Its fibers are much softer and more flexible than amphibolic asbestos, and they do less damage to body tissue. All six types of asbestos are composed of long chains of silicon and oxygen atoms, locked together with various metals, such as magnesium and iron, to form the whisker-like crystalline fibers that characterize this mineral.

Chrysotile is the most commonly used type of asbestos and accounted for about 98% of the worldwide asbestos production in 1988. It is usually white, and is sometimes known as white asbestos, although it can also be amber, gray, or greenish in color. Most chrysotile fibers are about 0.25-0.50 in (6.4-12.7 mm) long and are usually added to concrete mixes to provide reinforcement. Only about 8% of chrysotile fibers are long enough to be spun into fabric or rope.

Amosite, sometimes called brown asbestos, accounted for about 1% of worldwide production in 1988. It often has a light brown tinge, but is also found in dark colors, as well as white. Amosite has coarse fibers that are about 0.12-6.0 in (3.0-152.0 mm) long. The fibers are difficult to spin into fabric or rope and are mostly used as an insulating material, although that use is banned in many countries.

Crocidolite, sometimes called blue asbestos, accounted for the remaining 1% of world-wide production. It has a bluish tinge, and its fibers are about 0.12-3.0 in (3.0-76.0 mm) long. Crocidolite has very high tensile strength and excellent resistance to chemicals. One of its uses is as a reinforcement in plastics.

The other three types of asbestos—anthophyllite, actinolite, and tremolite—have no significant commercial applications and are rarely mined.

The Manufacturing
Process

Asbestos deposits are found underground, and the ore is brought to the surface for processing using conventional mining practices. Chrysotile asbestos is usually found near the surface and can be accessed with an open-pit mine. Other asbestos deposits are found at varying depths and may require tunnels as deep as 900 ft (300 m) to gain access.

Asbestos fibers are formed by the gradual growth of mineral crystals in cracks, or veins, found in soft rock formations. The crystals grow across the vein, and the width of the vein determines the resulting asbestos fiber length. Because the minerals come from the surrounding rock, the chemical composition of the fibers is similar to the rock. As a result the asbestos must be separated from the rocky ore using physical methods, rather than the chemical methods sometimes used to process other ores.

Here are the steps used to process the chrysotile asbestos ore commonly found in Canada:

Mining

  • Chrysoltile asbestos deposits are usually located using a magnetic sensor called a magnometer. This method relies on the fact that the magnetic mineral magnetite is often found near asbestos formations. Core drillings are used to pinpoint the location of the deposits and to determine the size and purity of the asbestos.

    Most chrysotile asbestos mining operations are conducted in an open-pit mine. A spiraling series of flat terraces, or benches, are cut into the sloping interior sides of the pit. These are used both as a work platform and as a roadway for hauling the ore up and out of the pit. The asbestos ore deposits are loosened from the surrounding rock by careful drilling and blasting with explosives. The resulting rocky debris is loaded into large rubber-tired haul trucks and brought out of the mine. Some operations use an excavation technique called block caving, in which a section of the ore deposit is under-cut until it crumbles under its own weight and slides down a chute into the waiting haul trucks.

Separating

The ore contains only about 10% asbestos, which must be carefully separated from the rock to avoid fracturing the very thin fibers. The most common method of separation is called dry milling. In this method, the primary separation is done in a series of crushing and vacuum aspirating operations in which the asbestos fibers are literally sucked out of the ore. This is followed by a series of secondary separation operations to remove rock dust and other small debris.

  • The ore is fed into a jaw crusher, which squeezes the ore to break it up into pieces that are 0.75 in (20.0 mm) in diameter or less. The crushed ore is then dried to remove any moisture that may be present.
  • The ore falls on the surface of a vibrating 30-mesh screen, which has openings that are 0.002 in (0.06 mm) in diameter. As the screen vibrates, the loosened asbestos fibers rise to the top of the crushed ore and are vacuumed off. Because the crushed ore is much denser than the fibers, only the very smallest rock particles get vacuumed off with the asbestos.
  • The very fine silt and rock particles that fall through the vibrating screen are called throughs or tailings and are discarded. The crushed ore pieces that remain on the screen are called overs and are moved to the next stage of processing.

    The crushed ore from the first screen is fed through a second crusher, which reduces the ore pieces to about 0.25 in (6.0 mm) in diameter or less. The ore then falls on another vibrating 30-mesh screen and repeats the process described in steps 3 and 4.

  • The process of crushing and vacuum aspiration of the asbestos fibers is repeated twice more. Each time the pieces of ore get smaller until the last asbestos fibers are captured and the remaining ore is so small that it falls through the screen and is discarded. This four-step process also separates the asbestos fibers by length. The longest fibers are broken free from the surrounding rock in the first crusher and are vacuumed off the first screen. Shorter length fibers are broken free and captured on each successive set of crushers and screens, until the shortest fibers are captured on the last screen.
  • The asbestos fibers and other material captured from each screen are carried suspended in a stream of air and run through four separate cyclone separators. The heavier debris and rock dust particles fall to the center of the whirling air stream and drop out the bottom of the separators.
  • The air then passes through four separate sets of filters, which capture the different length asbestos fibers for packaging.

Quality Control

Asbestos fibers are graded according to several factors. One of the most important factors is their length, since this determines the applications where they may be used and, therefore, their commercial value.

The most common grading system for chrysotile asbestos fibers is called the Quebec Standard dry classification method. This standard defines nine grades of fibers from Grade 1, which is the longest, to Grade 9, which is the shortest. At the upper end of the scale, Grades 1 through 3 are called long fibers and range from 0.74 in (19.0 mm) and longer down to 0.25 in (6.0 mm) in length. Grades 4 through 6 are called medium fibers, while Grades 7 through 9 are called short fibers. Grade 8 and 9 fibers are under 0.12 in (3.0 mm) long and are classified by their loose density rather than their length.

Other factors for establishing the quality of asbestos fibers include tests to determine the degree of fiber separation or openness, the reinforcing capacity of the fibers in concrete, and the dust and granule content. Specific applications may require other quality control standards and tests.

Health and
Environmental Effects

It is now generally accepted that inhalation of asbestos fibers can be associated with three serious, and often fatal, diseases. Two of these, lung cancer and asbestosis, affect the lungs, while the third, mesothelioma, is a rare form of cancer that affects the lining of the thoracic and abdominal cavities.

It is also now generally accepted that different types of asbestos, particularly the amphiboles, pose a greater health hazard than chrysotile asbestos.

Finally, it is recognized that other factors, such as the length of the fibers and the duration and degree of exposure, can determine the health hazard posed by asbestos. In fact some studies have shown that some asbestos-induced lung cancers only occur when the exposure is above a certain level of concentration. Below that threshold, there is no statistical increase in lung cancer over that found in the general population.

Although not everyone agrees with these findings, overall concerns about the potential adverse health effects of inhaling asbestos fibers have led to stricter regulations on the amount of airborne asbestos allow-able in the workplace. These regulations vary from one country to another, but they all mandate significantly lower levels than previously found. In the United States, the Occupational Health and Safety Administration (OSHA) set the maximum permissible exposure to fibers longer than 0.005 mm at 0.2 fibers/cubic centimeter during an eighthour workday or 40-hour work week.

Airborne asbestos levels in the general environment outside the workplace are many times lower and are not considered a hazard.

The Future

Asbestos is still an important component in many products and processes, although its usage is expected to remain low in the United States. The stricter exposure regulations and improved manufacturing and handling procedures now in place are expected to eliminate health problems associated with asbestos.

Where to Learn More

Books

Brady, George S., Henry R. Clauser, and John A. Vaccari. Materials Handbook, 14th Edition. McGraw-Hill, 1997.

Hornbostel, Caleb. Construction Materials, 2nd Edition. John Wiley and Sons, Inc., 1991.

Kroschwitz, Jacqueline I. and Mary Howe-Grant, ed. Encyclopedia of Chemical Technology, 4th edition. John Wiley and Sons, Inc., 1993.

Periodicals

Alleman, James E., and Brooke T. Mossman.

"Asbestos Revisited." Scientific American (July 1997): 70-75.

Other

http://www.asbestos-institute.ca.

http://www.epa.gov/ttnuatwl/hlthef/asbestos.html.

[Article by: Chris Cavette]


 

Any of six naturally occurring minerals characterized by being extremely fibrous (asbestiform), being incombustible, and having high tensile strength. Historically they were utilized in commerce for fire protection; for fiber-reinforcing material in tiles, plastics, and cements; for friction materials; and for thousands of other uses. Currently the vast majority of asbestos used worldwide is chrysotile type, which is used for asbestos cement, friction products, coating and compounds, and roofing products. Because of great concern over the health effects of asbestos, many countries have promulgated strict regulations or bans on its use.

The six naturally occurring minerals exploited commercially for their desirable physical properties, which are in part derived from their asbestiform habit, are chrysotile asbestos—a member of the serpentine mineral group; and anthophyllite asbestos, grunerite asbestos (known historically by the commercial name amosite), riebeckite asbestos (known historically by the commercial name crocidolite), tremolite asbestos, and actinolite asbestos—all members of the amphibole mineral group. Populations of these mineral fibers, however processed, can be demonstrated to be asbestos if the length varies independently of the diameter. The six minerals designated as asbestos also occur in a nonfibrous form.

The three principal diseases associated with exposure to the asbestos minerals are lung cancer; mesothelioma, a rare cancer of the pleural and peritoneal membranes that enclose the chest and abdominal cavities; and asbestosis, a nonmalignant disease characterized by a diffuse interstitial fibrosis of the lung, which causes the lung tissue to become stiff and exchange oxygen poorly. Excessive exposure to all the asbestos fiber types is associated with asbestosis and increased risk of lung cancer. Mesothelioma, a rare tumor accounting for approximately 1 in 10,000 deaths in the general population, can be dramatically increased by exposure to amosite, crocidolite, or tremolite asbestos. These last two fiber types are strongly associated with an increased incidence of nonoccupational mesothelioma and therefore are thought to present a risk at rather low exposures. See also Mutagens and carcinogens; Oncology.


 

Insulation material frequently used in older buildings as pipe wrap, boiler insulation, floor tile, and ceiling coating. Asbestos may become Friable (brittle) with age. In that condition, it may crumble and release particles which, like dust, become airborne. Breathing asbestos particles may cause several serious lung illnesses. Removal or encapsulation of asbestos in buildings is expensive but necessary to prevent illness. The discovery of asbestos in a building is likely to cause a significant value loss.

 
Hacker Slang: asbestos

[common] Used as a modifier to anything intended to protect one from flames; also in other highly flame-suggestive usages. See, for example, asbestos longjohns and asbestos cork award.


 

"Asbestos" is a term used to describe any of several naturally occurring fibrous silicate minerals of the amphibole or serpentine groups. Asbestos fibers may be straight (amphibole asbestos) or curled (serpentine asbestos), and have no detectable odor or taste. There are six minerals that are generally described as asbestos: chrysotile, which is a serpentine mineral; and crocidolite, amosite, tremolite, anthophyllite, and actinolite, which are all amphibole minerals. Asbestos fibers vary in length (usually greater than 5 microns), and width (usually less than 0.5 microns).

Almost 95 percent of the world's mined asbestos is chrysotile asbestos. The world has 200 million tons of identified asbestos resources, and an estimated 45 million tons of additional asbestos resources. Because asbestos fibers are resistant to heat and chemicals, they have been used in the production of building materials (e.g., floor tiles, roof shingles, cement), friction products (e.g., automotive brake pads), and heat-resistant fabrics. However, many countries, including the United States, have banned new uses of asbestos because of its adverse health effects. Worldwide use of asbestos has declined, but certain areas of the world (particularly Southeast Asia, South America, and Eastern Europe) continue to use it, in part because asbestos is an economical and long-lasting building material.

Humans can be exposed to asbestos through inhalation of asbestos fibers, as well as through ingestion (e.g., drinking water from cement pipes that have been manufactured with asbestos). Asbestos-related diseases commonly occur after a fifteen- to forty-year latency period following initial asbestos exposure, and are primarily associated with occupational inhalation exposure. Nonoccupational exposure to asbestos occurs primarily through exposure to asbestos that is "friable," meaning it can be reduced to dust by hand pressure. Asbestos fibers are long, thin fibers that can be inhaled deep into the lungs and are able to penetrate the lung's walls. The immune system is helpless against these fibers, because they are unable to be engulfed (phagocytised) by alveolar macrophages, and therefore remain in the lung for an extended period.

Diseases associated with asbestos exposure primarily involve the respiratory system and include progressive pulmonary fibrosis (asbestosis), pleural disease (the pleura are the membranes that cover the lungs), and cancer of the bronchi (bronchogenic carcinoma) and pleura (malignant mesothelioma). Cigarette smoking along with asbestos exposure increases the risk of lung cancer. There is disagreement within the scientific community as to the difference in the extent of toxicity between serpentine and amphibole asbestos fibers, although studies in humans and animals have demonstrated that both types of fibers increase the risk of asbestosis, malignant mesothelioma, and lung cancer.

The primary public health approach to asbestos is to ban or severely limit its use. In order to further reduce occupational disease from asbestos exposure, environmental controls should be implemented in the workplace, including ventilation systems, full-face respirators, and changing clothes before and after asbestos exposure.

(SEE ALSO: Lung Cancer; Occupational Lung Disease; Occupational Safety and Health)

Bibliography

Agency for Toxic Substances Disease Registry (1995). Toxicological Profile for Asbestos (Update). Washington, DC: U.S. Department of Health and Human Services.

International Agency for Research on Cancer (1987). "Asbestos and Certain Asbestos Compounds." In IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. IARC Monographs Supplement 7. Lyon: IARC.

International Programme on Chemical Safety (1986). Asbestos and Other Natural Mineral Fibers. Environmental Health Criteria 53. Geneva: World Health Organization.

—— (1998). Chrysotile Asbestos. Environmental Health Criteria 203. Geneva: World Health Organization.

United States Geological Survey (2000). Minerals Commodity Summaries: Asbestos. Available at http://minerals.usgs.gov/minerals/pubs/commodity/asbestos/index.html.

— MARGARET H. WHITAKER; BRUCE A. FOWLER



 

Any of several minerals that separate readily into long, flexible fibres. Chrysotile accounts for about 95% of all asbestos still in commercial use. The other types all belong to the amphibole group and include the highly fibrous forms of anthophyllite, amosite, crocidolite, tremolite, and actinolite. Asbestos fibre was used in brake linings, insulation, roofing shingles, floor and ceiling tiles, cement pipes, and other building materials. Asbestos fabrics were used for safety apparel and theatre curtains. In the 1970s it was found that prolonged inhalation of the tiny asbestos fibres can cause asbestosis, lung cancer, and/or mesothelioma, all serious lung diseases. The incidence of mesothelioma is most commonly associated with extensive inhalation of amphibole asbestos. In 1989 the U.S. government instituted a gradual ban on the manufacture, use, and export of most products made with asbestos.

For more information on asbestos, visit Britannica.com.

 
Architecture: asbestos, asbestos fiber

Fine, flexible, non-combustible, inorganic fiber obtained from natural hydrous magnesium silicate; can withstand high temperatures without change; a poor heat conductor; is fabricated into many forms either alone or with other ingredients. A recognized health hazard.


 
common name for any of a variety of silicate minerals within the amphibole and serpentine groups that are fibrous in structure and more or less resistant to acid and fire. Chrysotile asbestos, a form of serpentine, is the chief commercial asbestos. Varieties of amphibole asbestos are amosite, used in insulating materials; crocidolite, or blue asbestos, used for making asbestos-cement products; and tremolite, used in laboratories for filtering chemicals. Asbestos is usually found comprising veins in other rock; in most cases it appears to be the product of metamorphism. Canada is the chief asbestos producing country; other producers are Russia, Zimbabwe, the Republic of South Africa, Cyprus, and the United States. Asbestos is mined both in open quarries and underground.

Since the 1960s, asbestos has been recognized as a potent carcinogen and serious health hazard. Inhalation of airborne asbestos fibers has been established as the cause of asbestosis (thickening and scarring of lung tissue) and as a cause of mesothelioma (a highly lethal tumor of the pleura) as well as of cancers of the lung, intestines, and liver. In 1972, the Occupational Safety and Health Administration began regulating asbestos and strengthening work safety standards. Large class action lawsuits were filed and won against asbestos companies, which had probable prior knowledge of the dangers involved. In 1989, the Environmental Protection Agency imposed a ban on 94% of U.S. asbestos production and imports, to be phased in over a seven year period. Most current asbestos exposure comes from asbestos in older buildings and products such as automobile brakes.

Bibliography

See P. H. Riordon and V. F. Hollister, Geology of Asbestos Deposits (1981); S. S. Chissick and R. Derricott, Asbestos: Properties, Applications and Hazards (1983).


 

Asbestos is so called from being inextinguishable even by showers and storms, if once set on fire. The name derives from an ancient Greek term for a fabulous stone. Pagan peoples made use of it for lights in their temples. Plutarch records that the Vestal Virgins used perpetual lamp wicks, while Pausanias mentions a lamp with a wick that was not consumed, being made from a mineral fiber from Cyprus. Asbestos is of woolly texture and is sometimes called the Salamander's Feather. Leonardus stated: "Its fire is nourished by an inseparable unctuous humid flowing from its substance; therefore, being once kindled, it preserves a constant light without feeding it with any moisture."

 

A naturally occurring amphibole mineral in fibrous form with the fibers lying in parallel in plates; causes asbestosis in humans. Called also horneblende.


 
Wikipedia: asbestos
Fibrous asbestos on muscovite
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Fibrous asbestos on muscovite
Asbestos
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Asbestos
Asbestos
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Asbestos
Blue asbestos (crocidolite) from Wittenoom, Western Australia. The ruler is 1 cm.   Blue asbestos showing the fibrous nature of the mineral
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Blue asbestos (crocidolite) from Wittenoom, Western Australia. The ruler is 1 cm.
Blue asbestos showing the fibrous nature of the mineral
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Blue asbestos showing the fibrous nature of the mineral

The word Asbestos is derived from a Greek adjective meaning inextinguishable. It is distinguished from other minerals by the fact that its crystals form long, thin fibers. Deposits of asbestos are found throughout the world. The primary sites of commercial production are: the Commonwealth of Independent States, Canada, Brazil, Zimbabwe, Russia and South Africa.

The Greeks termed asbestos the "miracle mineral" because of its soft and pliant properties, as well as its ability to withstand heat. Asbestos was spun and woven into cloth in the same manner as cotton. It was also utilized for wicks in sacred lamps. Romans likewise recognized the properties of asbestos and it is thought that they cleaned asbestos tablecloths by throwing them into fire.[citation needed]

Asbestos became increasingly popular among manufacturers and builders in the late 19th century due to its resistance to heat, electricity and chemical damage, sound absorption and tensile strength. 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 serious illnesses, including mesothelioma. Since the mid 1980s, many uses of asbestos are banned in many countries.

Types of asbestos and associated fibres

Chrysotile asbestos
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Chrysotile asbestos
Asbestos fibers
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Asbestos fibers

Six 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.[1] 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.[2] 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.[3]

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.[2] This type of asbestos, like all asbestos, is 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 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 crystal structure containing strongly bonded ribbonlike silicate anion polymers that extend the length of the crystal . Serpentine (chrysotile) has a sheetlike silicate anion which is curved, and rolls up like a carpet to form the fiber.[4] Tremolite often contaminates 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)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.

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 read the EPA's clarification statement.[5]

Production trends

Asbestos output in 2005
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Asbestos output in 2005

In 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.[6]

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.[7][8] Charlemagne, the first Holy Roman Emperor, is said to have had a tablecloth made of asbestos.[9][10][11]
Wealthy Persians, who bought asbestos imported over the Hindu Kush, amazed guests by cleaning the cloth in simply by exposing it to fire. According to Biruni in his book of Gems, any cloths made of asbestos (Persian: آذرشست, āzarshast or Persian: آذرشب, āzarshab) were called (Persian: شستكه) shastakeh[12]. Some of the Persians believed the fiber was fur from an animal (named samandar, Persian: سمندر) that lived in fire and died when exposed to water.[13][14]
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.[15] Others assert that the ancients used asbestos to make perpetual wicks for sepulchral or other lamps.[11][13] 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.[15]

Asbestos became more widespread during the industrial revolution, in the 1860s it was used as insulation in the U.S. and Canada. Development of the first commercial asbestos mine began in 1879 in the Appalachian foothills of Quebec.[16] 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.[11]

Approximately 100,000 people have died, or will die, from asbestos exposure related to ship building. In the Hampton Roads area, a shipbuilding center, mesothelioma occurrence is seven times the national rate.[17] Thousands of metric tons of asbestos were used in World War II 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.[16]

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.[18]

The first documented death related to asbestos was in 1906.[10] In the early 1900s 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.[8] England protected asbestos workers about ten years sooner than the U.S. By the 1930s, England regulated ventilation and made asbestos an excusable work related disease.[8][19] The term Mesothelioma was not used in medical literature until 1931, and wasn't associated with asbestos until sometime in the 1940s.[10]

The United States government and asbestos industry have been criticized for not acting quickly enough to inform the public of dangers, and to reduce public exposure. In the late 1970s court documents proved that asbestos industry officials knew of asbestos dangers and tried to conceal them.[16]

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.[20]

Modern usage

Serpentine group

Serpentine minerals have a sheet or layered structure. Chrysolite is the only asbestos mineral in the serpetine group. In the United States, chrysotile has been the most commonly used type of asbestos. According to the U.S. EPA Asbestos Building Inspectors Manual, chrysotile accounts for approximately 95% of asbestos found in buildings in the United States. 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[21] 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.[22] 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.[22]

Amphibole group

Five types of asbestos are found in the amphibole group: amosite, crocidolite, anthophyllite, tremolite, and actinolite. Amosite, the second most likely type to be found in buildings, according to the U.S. EPA Asestos Building Inspectors Guide, is the "brown" asbestos.

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

By the first century, Greeks and Romans had already observed, at least in passing, that slaves involved in the weaving of asbestos cloth were afflicted with a sickness of the lungs. [23].

Prior to 1900

Early concern about the health effects of asbestos exposure can be found in several sources. Among the earliest were reports in Britain. The annual reports of the Chief Inspector of Factories reported as early as 1898 that asbestos had 'easily demonstrated' health risks[24]

At about the same time, what was probably the first study of mortality among asbestos workers was reported in France [25]. While the study describes the cause of death as chalicosis, a generalized pneumoconiosis, the circumstances of the employment of the fifty workers whose death prompted the study suggest that the root cause was asbestos or mixed asbestos-cotton dust exposure.

1900s - 1910s

Further awareness of asbestos-related diseases can be found in the early 1900s, when London doctor H. Montague Murray conducted a post mortem exam on a young asbestos factory worker who died in 1899. Dr. Murray gave testimony on this death in connection with an industrial disease compensation hearing. The post-mortem confirmed the presence of asbestos in the lung tissue, prompting Dr. Murray to express as an expert opinion his belief that the inhalation of asbestos dust had at least contributed to, if not actually caused, the death of the worker[26].

The record in the United States was similar. Early observations were largely anecdotal in nature and did not definitively link the occupation with the disease, followed by more compelling and larger studies that strengthened the association. One such study, published in 1918, noted:

All of these processes unquestionably involve a considerable dust hazard, but the hygienic aspects of the industry have not been reported upon. It may be said, in conclusion, that in the practice of American and Canadian life insurance companies asbestos workers are generally declined on account of the assumed health-injurious conditions of the industry [27].

1920s and 1930s

Widespread recognition of the occupational risks of asbestos in Britain was reported in 1924 by a Dr. Cooke, a pathologist, who introduced a case description of a 33-year old female asbestos worker with the following: 'Medical men in areas where asbestos is manufactured have long suspected the dust to be the cause of chronic bronchitis and fibrosis...[28]." Dr. Cooke then went on to report on a case in 1927 involving a 33-year old male worker who was the only survivor out of ten workers in an asbestos carding room. In the report he named the disease "asbestosis[29]."

Dr. Cooke's second case report was followed, in the late 20's, by a large public health investigation (now known as the Merewether report after one of its two authors) that examined some 360 asbestos-textile workers (reported to be about 15% of the total comparable employment in Britain at the time) and found that about a quarter of them suffered from pulmonary fibrosis [30]. This investigation resulted in improved regulation of the manufacturing of asbestos-containing products in the early 1930s. Regulations included industrial hygiene standards, medical examinations, and inclusion of the asbestos industry into the British Workers' Compensation Act [31].

The first known US workers' compensation claim for asbestos disease was in 1927[32]. In 1930, the first reported autopsy of an asbestosis sufferer was conducted in the United states and later presented by a doctor at the Mayo Clinic, although in this case the exposure involved mining activities somewhere in South America[33].

In 1930, the major asbestos company Johns-Manville produces a report, for internal company use only, about medical reports of asbestos worker fatalities.[34] In 1932, A letter from U.S. Bureau of Mines to asbestos manufacturer Eagle-Picher states, in relevant part, "It is now known that asbestos dust is one of the most dangerous dusts to which man is exposed".[35] In 1933, Metropolitan Life Insurance Co. doctors find that 29 percent of workers in a Johns-Manville plant have asbestosis.[34] Likewise, in 1933, Johns-Manville officials settle lawsuits by 11 employees with asbestosis on the condition that the employees' lawyer agree to never again "directly or indirectly participate in the bringing of new actions against the Corporation."[35] In 1934, officials of two large asbestos companies, Johns-Manville and Raybestos-Manhattan, edit an article about the diseases of asbestos workers written by a Metropolitan Life Insurance Company doctor. The changes minimize the danger of asbestos dust.[35] In 1935, officials of Johns-Manville and Raybestos-Manhattan instruct the editor of Asbestos magazine to publish nothing about asbestosis.[35] In 1936, a group of asbestos companies agrees to sponsor research on the health effects of asbestos dust, but require that the companies maintain complete control over the disclosure of the results.[34]

1940s

In 1942, an internal Owens-Corning corporate memo refer to "medical literature on asbestosis . . . . scores of publications in which the lung and skin hazards of asbestos are discussed."[36] Either in 1942 or 1943, the president of Johns-Manville, Lewis H. Brown, says that the managers of another asbestos company were "a bunch of fools for notifying employees who had asbestosis." When one of the managers asks, "do you mean to tell me you would let them work until they dropped dead?" The response is reported to have been, "Yes. We save a lot of money that way."[37] In 1944, a Metropolitan Life Insurance Company report finds 42 cases of asbestosis among 195 asbestos miners.[38]

1950s

In 1951, asbestos companies removed all references to cancer before allowing publication of research they sponsor.[39]. In 1952, Dr. Kenneth Smith, Johns-Manville medical director, recommends (unsuccessfully) that warning labels be attached to products containing asbestos. Later, Smith testifies: "It was a business decision as far as I could understand . . . the corporation is in business to provide jobs for people and make money for stockholders and they had to take into consideration the effects of everything they did and if the application of a caution label identifying a product as hazardous would cut into sales, there would be serious financial implications."[40]. In 1953, National Gypsum's safety director writes to the Indiana Division of Industrial Hygiene, recommending that acoustic plaster mixers wear respirators "because of the asbestos used in the product." Another company official notes that the letter is "full of dynamite," urges that it be retrieved before reaching its destination. A memo in the files notes that the company "succeeded in stopping" the letter, which "will be modified."[41].

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.[42] 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 US 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.[43]

Portions of El Dorado county are known to contain natural asbestos formations near the surface.[44][43] 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".[45]

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.[43]

Asbestos in the environment

Asbestos is in the air we breathe and some of the water we drink, including water from natural sources.[46] Studies have shown that members of general (non-occupationally 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.[47]

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). The 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.[48]

Asbestos is not part of a ASTM E 1527-05 Phase I Environmental Site Assessment (ESA). A Building Survey for Asbestos is considered an out-of-scope consideration under the industry standard ASTM 1527-05 Phase I ESA (see ASTM E 1527-05). ASTM Standard E 2356-04 should be consulted by the owner or owners' agent to determine which type of asbestos building survey is appropriate, typically either a baseline survey or a design survey of functional areas. Both types of surveys are explained in detail under ASTM Standard E 2356-04. Typically, a baseline survey is performed by an EPA (or State) licensed asbestos inspector. The baseline survey provides the buyer with sufficient information on presumed asbestos at the facility, often which leads to reduction in the assessed value of the building (due primarily to forthcoming abatement costs). Note: EPA NESHAP and OSHA Regulations must be consulted in addition to ASTM Standard E 2356-04 to ensure all statutory requirments are satisfied, ex. notification requirements for renovation/demolition. Asbestos is not a material covered under CERCLA's innocent purchaser defense.

In some instances, the U.S. EPA includes asbestos contaminated facilities on the Superfund National Priorities list (NPL). Buyers should be careful not to purchase facilities, even with a ASTM E 1527-05 Phase I ESA completed, without a full understanding of all the hazards in a building or at a property, without evaluating non-scope ASTM E 1527-05 materials, such as asbestos, lead, PCBs, mercury, radon, et al. A standard ASTM E 1527-05 does not include asbestos surveys as standard practice.

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 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



Main article: Asbestos and the law

Asbestos litigation is the longest, most expensive mass tort in U.S. history, involving more than 8,400 defendants and 730,000 claimants as of 2002 according to the RAND Corporation[49], and at least one defendant reported claim counts in excess of 800,000 in 2006[50].

Current trends indicate that the worldwide rate at which people are diagnosed with the disease will likely increase through the next decade[51]. Analysts have estimated that the total costs of asbestos litigation in the USA alone is over $250 billion.[52]

Litigation exists outside the United States in England, Scotland, Ireland, the Netherlands, France, Australia, and Japan among other nations. See the companion article for further information.

The volume of the asbestos liability has concerned manufacturers and insurers and reinsuers[53]. 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

According to Natural Resources Canada, chrysotile asbestos is not as dangerous as once thought. According to their fact sheet, "...current knowledge and modern technology can successfully control the potential for health and environmental harm posed by chrysotile".[54] In May of 1998, Canada requested consultations with the European Commission concerning France's 1996 prohibition of the importation and sale of asbestos.[55]

Canada claimed that the French measures contravened provisions of the Agreements on Sanitary and Phytosanitary Measures and on Technical Barriers to Trade, and the GATT 1994.[55]

The EC said that substitute materials had been developed in place of asbestos, which are safer to human health. It stressed that the French measures were not discriminatory, and were fully justified for public health reasons. The EC said that in the July consultations, it had tried to convince Canada that the measures were justified, and that just as Canada broke off consultations, it was in the process of submitting substantial scientific data in favour of the asbestos ban.[55]

Critics of Canada's support of the use of chrysotile asbestos argue that Canada is ignoring the risks associated with the material. The CFMEU pointed out that selling asbestos is illegal in Canada, but it is exported and most exports go to developing countries. Canada has pressured countries, including Chile, and the UN to avoid asbestos bans[56]

Asbestos regulation critics include the controversial Junkscience.com author and Fox News columnist Steven Milloy and the asbestos industry.[57] 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.[58][59] 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.[60][59]

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.[61] Steven Milloy suggests that the World Trade Center towers could still be standing or at least would have stood longer had a 1971 ban not stopped the completion of the asbestos coating above the 64th floor.[62] 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.[63][64][65]

Substitutes for asbestos in construction

Fiberglass insulat