Asbestos

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Asbestos (pronounced /æsˈbɛstəs/ or /æzˈbɛstəs/) is a set of six naturally occurring silicate

minerals used commercially for their desirable physical properties. They all have in common

their eponymousasbestiform habit: long (roughly 1:20 aspect ratio), thin fibrouscrystals. The

prolonged inhalation of asbestos fibers can cause serious illnessesincluding malignant lung

cancer, mesothelioma, and asbestosis (a type of pneumoconiosis). The trade and use of asbestos

have been restricted or banned in many jurisdictions. Asbestos became increasingly popular

among manufacturers and builders in the late 19th century because of its sound absorption,

average tensile strength, its resistance to fire, heat, electrical and chemical damage, and

affordability. 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. Asbestos mining

began more than 4,000 years ago, but did not start large-scale until the end of the 19th century.

For a long time, the world's largest asbestos mine was the Jeffrey mine in the town of Asbestos,

Quebec.

as•bes•tos (æsˈbɛstəs, æz-)

1. a fibrous mineral, either amphibole or chrysotile, formerly used for making incombustible or

fireproof articles and in building insulation.

2. a fabric woven from asbestos fibers, formerly used for theater curtains, firefighters' gloves,

etc.

Asbestos has been a highly visible issue in public health for over three decades. During the mid- to late-

20th century, many advances were made in the scientific understanding of worker health effects from

exposure to asbestos fibers and other elongate mineral particles (EMPs). It is now well documented that

asbestos fibers, when inhaled, can cause serious diseases in exposed workers. However, many questions

and areas of confusion and scientific uncertainty remain.

Asbestos includes chrysotile, amosite, crocidolite, tremolite asbestos, anthophyllite asbestos, actinolite

asbestos, and any of these minerals that have been chemically treated and/or altered.

Asbestos-containing material (ACM) means any material containing more than 1% asbestos.

Asbestos fibers fabric may therefore be easily weaved into fire-resistant security attire regarding save

authorities along with firefighters. Things pertaining to other pros along with workers, who will be

subjected to high heat, can also be manufactured, developing mesothelioma items threat

DISADVANTAGE

Asbestos fibers is just not any hazard though it really is in fantastic issue, but when asbestos fiber

becomes crumbly combined with okay dust-like fibers become air-borne, they’re going to result in

significant well-being results, 15-40 many years along the monitor. Asbestosis is caused by skin damage

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with the lung area, due to asbestos fibers materials lodging right now there. Exposure to asbestos may

also result in mesothelioma, the unusual cancer with the upper body, heart as well as stomach coating.

How is Asbestos Made?

Asbestos is not made, it is mined. Different colors of asbestos can be found in mines all

across the world. White asbestos, called chrysotile, comes from mines in Europe and

United States. Brown asbestos, amosite, is commonly found in African mines. Blue

asbestos, crocidolite, is found in South Africa and Australia. Because of this mineral's

abundance and the low cost of obtaining it, no attempt to artificially synthesize it has ever

been made.

Expert Insight

Asbestos is a naturally occurring substance which is obtained from the soil through open

pit mining. Asbestos is mined as a rock-like ore. Though it comes in various types, colors

and densities, it is easily identifiable through the mining process. Asbestos is still mined

throughout many parts of the world in large, modernized open pit mines.

Types of Asbestos

Asbestos refers to six unique substances that belong to the serpentine and amphibole mineral

families. These terms do not refer to mineral descriptions but to a broad term that refers to

unique fibers. According to the Toxic Substances Control Act (TSCA), the asbestiform varieties

of the following minerals are classified as asbestos:

Chrysotile

- This is the most commonly used form of asbestos and can be found today in roofs, ceilings,

walls and floors of homes and businesses. Chrysotile asbestos also was used in automobile brake

linings, pipe insulation, gaskets and boiler seals. Although it is more prevalent, some studies

show it takes more exposure to chrysotile than other types of asbestos to develop related

diseases.

Amosite

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- This is known as brown asbestos, and it originates mostly in Africa. It was used most

frequently in cement sheet and pipe insulation. It can be found in insulating board (which

contained up to 40 percent asbestos), ceiling tiles and in thermal insulation products. Like the

other forms of amphibole asbestos, it has needle-like fibers.

Crocidolite

This is blue asbestos and its known for having the best heat resistance. Mined mostly in South

Africa, Bolivia and Australia, this is seen as the most dangerous type of asbestos. Crocidolite

was commonly used to insulate steam engines, and it was found in some spray-on coatings, pipe

insulation and cement products.

Tremolite

- This is not used commercially, but it can be found as a contaminant in chrysotile asbestos,

vermiculite and talc powders. It was occasionally found as a contaminant in certain asbestos-

containing insulation products, paints, sealants and roofing materials. Tremolite can be white,

green, gray and even transparent.

Anthophyllite

- This type was mined primarily in Finland and displays a gray-brown color. It was not

commercially used and was rather found as a contaminant. Anthophyllite was most commonly

found in composite flooring.

While the name "asbestos" goes back to ancient times, the Environmental Protection Agency created a

legal definition for the word asbestos by limiting the term to 6 specific fibrous minerals from two distinct

groups: chrysotile (from the Serpentine group); and amosite, crocidolite, tremolite, actinolite and

anthophyllite (from the Amphibole group). OSHA defines an asbestos fiber as having a length > 5mm

and a length:width ratio of 3:1. EPA, on the other hand, defines a particle as a fiber if the ratio is >5:1

length:width when analyzing bulk samples.

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Chemical and Physical Properties

For all practical purposes most forms of asbestos are inert. That is one quality that makes them

so desirable in industry. They are insoluble in water and organic solvents and are nonflammable.

While the serpentine chrysotile is soluble in acid, the amphiboles amosite, crocidolite and

anthophyllite are resistant to acids. Interestingly enough, most asbestos minerals have non-

asbestos counterparts with identical chemical compositions. In the case of tremolite,

anthophyllite and actinolite, the word "asbestos" is added after the mineral name to distinguish it

from the non-asbestos form. Chrysotile, crocidolite and amosite do not require "asbestos" to be

added because the non-asbestos forms have different names.

Fibrous forms and non-fibrous forms of a mineral may occur in the same deposits. That would

make sense when one considers how asbestos is formed. It would seem very likely that

temperature and pressure might be sufficient to metamorphose completely some but not all of the

igneous rock into the asbestos form.

Physical characteristics of Asbestos

Asbestos has a host of physical properties that make it almost a superstar in the world of

industrial chemistry. Its tensile strength surpasses that of steel. It has tremendous thermal

stability, thermal and electrical resistance and is non-flammable. It can be subdivided into fine

fibers that are strong enough and flexible enough to be spun into material that is a flame

retardant, chemically inert thermal and electrical insulator. Note that asbestos binds with better

insulating materials to create the ultimate construction materials.

Asbestos fibers have no detectible odor or taste. They are all solids that do not move through soil

and are insoluble in water. Its color will vary according to type, and metallic composition.

Crocidolite, which has iron and sodium as its only metallic elements, is the most colorful,

adorned in a range of colors including shades of lavender, blue and green. In general, asbestos-

containing iron may display a green color ranging from a hint of green to solid green depending

upon the amount of iron present.

Tremolite contains no iron, but is part of a continuous mineral series with actinolite, in which

iron and magnesium can freely substitute with each other. As a result, some specimens of

tremolite may show a hint of pale green. Chrysotile and tremolite, which in pure form contain no

iron, tend to be white, together with actinolite and anthophyllite are grouped together as "white

asbestos" and classified as UN2590 (under the United Nations chemical ID numbering system).

Amosite and crocidolite are classified as UN2212. Amosite and crocidolite have been used

extensively for commercial use, and are considered to be extremely hazardous. Chrysotile is

more flexible and has been considered to be less hazardous than either amosite or crocidolite.

Until now, anthophyllite, actinolite and tremolite have been lumped with the "lesser evil"

chrysotile under the UN Identification numbering system. Their occurrence in industry has been

less extensive. Tremolite has been used in laboratories for filtering chemicals. Actinolite is used

for industrial asbestos. There is not much reported use of anthophyllite. All three of these

amphiboles also have non-asbestos forms associated with them in nature.

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Chemistry

Individual asbestos fibers are invisible to the unaided human eye because their size is about 3–

20 µm wide and can be as slim as 0.01 µm. Human hair ranges in size from 17 to 181 µm in

breadth.[55]

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, and in this case,

there are two cleavage planes which are much weaker than the third. 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.

When fibers or asbestos structures from asbestos containing materials (ACM) become airborne,

the process is called primary release. Primary release mechanisms include abrasion, impaction,

fallout, air erosion, vibration, and fire damage. Secondary release occurs when settled asbestos

fibers and structures are resuspended as a result of human activities. In unoccupied buildings or

during unoccupied periods, fiber release typically occurs by fallout or is induced by vibration or

air erosion.[56]

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 because of 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.

History of Asbestos Fiber

The first recorded use of the word asbestos is by Pliny the Elder in the 1st century ad, although the

substance itself was known as early as the 2nd century bc. The Romans made cremation cloths and

wicks from it, and centuries later Marco Polo noted its usefulness as cloth.

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 (see Asbestos-ceramic). The word asbestos comes from the ancient

Greek ἄσβεστος, meaning "unquenchable" or "inextinguishable". One of the first descriptions of a

material that may have been asbestos is in Theophrastus, On Stones, from around 300 BC, although this

identification has been questioned.The naming of minerals was not very consistent in ancient times. In

both modern and ancient Greek, the usual name for the material known in English as "asbestos" is

amiantos ("undefiled", "pure")

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Use of Asbestos fiber

Asbestos is a nonmetallic mineral fiber, which is nonflammable. The fiber is woven into fabrics and used

for theater curtains and industrial uses where flame-resistant materials are needed. The fibrous form of

several minerals and hydrous silicates of magnesium. The name may also be applied to the fibrous forms

of calcium and iron. Asbestos fibers can be molded or woven into various fabrics. Because it is

nonflammable and a poor heat conductor, asbestos has been widely used to make fireproof products

such as safety clothing for fire fighters and insulation products such as hot-water pipin

Uses of Asbestos

Asbestos is strong, fire-resistant, flexible and a good thermal insulator. These qualities

encouraged its use in a variety of products. It is used for thermal insulation, fire proofing,

acoustic insulation, roofing, flooring and in a variety of other building materials.

People are known to have uses asbestos materials for over a thousand years. However its use

became much more from the early 1900's onwards since which time it has been used in

thousands of construction, industrial, maritime and consumer products.

Asbestos-containing products include:-

Building and construction materials:

(asbestos cement pipe, insulating cement, insulating block, pipe covering, acoustical

panels/plaster, fire brick, vinyl-asbestos and asphalt-asbestos floor tile, linoleum backing, ceiling

tile, duct insulation for heating, ventilation and air conditioning (HVAC) systems, roofing felt,

transite furnace flue, transite shingles and sidings, insulated electrical wire and panels,

fireproofing spray, fire door interiors, refractory and boiler insulation materials)

Textiles (e.g. asbestos cloth in fireproof aprons, glassblower mitts)

Caulking compounds and panes (mastics, adhesives, coatings, joint compound, putty, acoustical

textures)

Friction products (brake linings, clutch assemblies and gaskets).

Some of these products contained a very high proportion of asbestos, while others contained only

small amounts.

These asbestos materials were widely used in the UK in industrial sites, homes, schools,

shipyards and commercial buildings until the late 1960's when health dangers associated with

their use became more widely known. A lot of asbestos material was then removed from the

1970's onwards. This involved further exposure of workers to asbestos as they removed the

materials from old buildings.

Trades Involving Asbestos Exposure

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Asbestos-containing products have been widely used, in one form or another, across a range of

industries including shipbuilding and repair, railways, building construction and maintenance,

power stations, steelworks, and motor vehicle industries.

As a consequence people from a wide range of occupations may have been exposed to airborne

asbestos fibres :

asbestos factory employees

aerospace workers

automobile mechanics

boilermakers

boilermen

bricklayers

carpenters

coal miners

construction workers

dockers

electricians

general builders

insulation engineer

iron workers

lab technicians

laggers

merchant navy cadets

merchant navy deck officers

non-asbestos factory employees

plasterers

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plumbers

refractory bricklayers in power stations

window fitters

sheet metal workers

shipyard workers

steam fitters

tile setters

turbine/boiler operators in power stations

welders

Workers in old buildings can also be exposed to asbestos used in the construction materials

Manufacturing Process of Asbestos

Asbestos is of two principal classes, the amphiboles and the serpentines, the former of relatively minor

importance. Chrysotile, in the serpentine class, constitutes most of the world supply of asbestos.

Countries that have produced asbestos include Russia, Kazakhstan, China, Brazil, and Canada.

Asbestos is obtainable by various underground mining methods, but the most common method is open-

pit mining. Only about 6 percent of the mined ore contains usable fibers.

The fibers are separated from the ore by crushing, air suction, and vibrating screens, and in the process

are sorted into different lengths, or grades. The most widely used method of grading, the Québec

Standard Test Method, divides the fibers into seven groups, the longest in group one and the shortest,

called milled asbestos, in group seven. The length of the fibers, as well as the chemical composition of

the ore, determines the kind of product that can be made from the asbestos. The longer fibers have

been used in fabrics, commonly with cotton or rayon, and the shorter ones for molded goods, such as

pipes and gaskets

Properties of Asbestos

Many substances burn when they are heated. Others melt or evaporate. Some substances, such as

asbestos, do not change when they are heated. This property can be very useful. For centuries, people

have known that this fibrous mineral has many useful properties. It is fire resistant. It does not melt or

react with air, at least not until it gets very hot. One form of the mineral withstands temperatures up to

2750 °C. It is a very good insulator. It is strong. It resists acid. It is chemically inactive. It can be woven

into cloth. Asbestos has some very useful properties, and it is readily available at a low cost.

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TABLE 8

ASBESTOS: WORLD PRODUCTION, BY COUNTRY1, 2

(Metric tons)

Country3 2001

2002

2003

2004

2005

e

Argentina 203 155

166

267

r 270

Brazil, fiber

172,695

194,750

194,350

194,800

195,000

Bulgaria

e

350

300

300

300

300

Canada

276,790

240,500

200,500

200,000

e 200,000

China

e

310,000

562,000

r 500,000

r 510,000

r 520,000

Colombia, crude ore

96,140

62,785

60,000

e 60,000

e 60,000

Egypt

e

--

r --

r --

r --

r --

India

e

21,000

18,000

19,000

18,000

19,000

Irane

2,000

1,500

1,470

r,

4 6,000

r,

4 5,000

Japane

--

r --

r --

r --

r --

Kazakhstan

271,300

291,100

354,500

346,500

355,000

Russiae

750,000

775,000

878,000

4 923,000

r,

4 925,000

Serbia and Montenegro 194

372

111

r 110

r 100

South Africa, chrysotile

13,393

--

6,218

r --

r --

4

United States, sold or used

by producers 5,260

2,720

--

--

--

Zimbabwe 136,327

168,000

e 147,000

104,000

r 122,041

4

Total 2,060,000 r 2,320,000

r 2,360,000

r 2,360,000

r 2,400,000

eEstimated.

rRevised. -- Zero.

1World totals, U.S. data, and estimated data are rounded to no more than three significant

digits; may not add to totals shown. 2Marketable fiber production. Table includes data available through April 8, 2006.

3In addition to the countries listed, Afghanistan, North Korea, Romania, and Slovakia also

produce asbestos, but output is not officially

reported, and available general information is inadequate for the formulation of reliable

estimates of output levels. 4Reported figure.

Chemical Properties of Asbestos

One of the more important theories concerning formation of asbestos recognizes that the primary

rock formation out of' which asbestos mother rock emerged is of volcanic origin. In Canada and

other important asbestos areas, this green colored mother rock is principally olivine, classified

chemically as magnesium silicate.

The pH of asbestos is generally listed as 9 to 10. When asbestos is acid washed or subjected to

other chemicals, it can be made to behave tisfctôrily with acid curing poly mers or resin systems

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The chemical feature common to all asbestos is that they are hydrated silicates The degree of

hydration varies from approximately one per cent in some types to as much as approximately 14

per cent in most kinds of chiysotile It generally accepted that asbestos is a metamorphic product

derived from certain types of silica-bearing minerals.

Effects of Chemicals on Asbestos

Published data showing the effect of chemicals on asbestos are given inTable 2.9 below. it is

reported that room temperature tests were conducted for periods of 24, 192, 360, and 528 hr. *

ASTM (D577-52, Method D39, Section 10) tensile grab test.

Inasmuch as most of the fibers reached maximum solubility after 528 hr, only this period was

reported.

TABLE 2.9: SOLUBILITY OF ASBESTOS [Click to enlarge]

Per Cent Loss in Weight, Refluxing Two Hours, 25% Acid or Caustic

* Badollet, M. S., "Asbestos, A Mineral of Unparalleled Properties," Can. Mining and Met. Bull. (1951).

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Effects of Heat on Asbestos

When asbestos is exposed to heat, it loses water of crystallization. At approximately 800°F,

hornblende asbestos generally loses the greatest part of its combined water while serpentine loses

only approximately 15 per cent. Hornblende asbestos becomes extremely brittle at 750°F.

In the case of serpentine asbestos, flexibility remains. Table 2.10 below gives the percentages of

loss in weight versus temperatures up to 1,800°F. Test specimens were predried to remove

surface water and weighed; After heat exposure for two hours, the asbestos was cooled at room

temperature in a desiccator prior to reweighing. If asbestos were cooled in the open room,

moisture from the air would be absorbed and weights would differ.

When asbestos fibers are dehydrated, they change in such properties as mechanical strength.

Water content in asbestos includes hygroscopic moisture adhering to the asbestos sur- face and

the chemically combined water of crystallization.

The content of hygroscopic moisture in asbestos has no rela tionship to its chemical composition.

It is directly related to such an environmental condition, as degree of relative humidity in the air.

Removal of this moisture can be accom- pushed by subjecting asbestos to a temperature of

approxi35 mately 212°F. At a relative humidity of approximately 40 per cent, moisture pickup in

asbestos after equilibrium is reported to be approximately 1 per cent; at 70 per cent relative

humidity, the total pickup is 1.5 per cent; at 95 per cent relative humidity, the total pickup is 2.5

per cent.

TABLE 2.10. EFFECT OF TEMPERATURE ON Loss IN WEIGHT OF ASBESTOS FIBERS * [click to enlarge]

* Can. Mining and Met. Bull. (1951). ! Iron changing in weight caused by oxidation.

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The Acid Resistance of Asbestos: Acid Washed Asbestos Fiber

The acid resistance of asbestos is important in a number of such different applications as

corrosion resistant plastic, cement equipment, and filters. In some applications, it is desirable to

remove all metallic and foreign matter. Mechanical devices as well as chemical, cleaning or

washing processes are used.

With regard to the chemical process, the general proce- dure is to immerse asbestos in a boiling

solution of 15 to 25 per cent hydrochloric acid. One to two hour immersion is generally

sufficient. After the acid washing, the asbestos is subjected to water rinsing. The water will

remove all free chlorine and neutralize the fiber. This process generally produces a loss of

approximately 10 per cent, by weight, of . the original asbestos. Loss in weight is due to removal

of the metallic and foreign matter.

The acid washed fibers are dried in order to make them useful in such other processes as

treatment with plastic or rubber resins.

Rank Country World Production, By Country (Metric tons)

1 Russian Federation 1,000,000

2 China 380,000

3 Brazil 288,000

4 Kazakhstan 230,000

5 Canada 150,000

6 India 19,000

7 Argentina 290

Source: United States Geological Survey (USGS) Minerals Resources Program

Note: Check source table for details and footnotes

Year of Estimate: 2009