Asbestos (pronounced /æsˈbɛstəs/ or /æzˈbɛstəs/) is a set of six naturally
occurring silicate minerals which all have in common their eponymous
asbestiform habit: long (roughly 1:20 aspect ratio), thin fibrous crystals.
Asbestos mining began more than 4,000 years ago, but did not start large-
scale until the end of the 19th century when manufacturers and builders
used asbestos because of its desirable physical properties: 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
or woven into fabric or mats.
The prolonged inhalation of asbestos fibers can cause serious illnesses
including malignant lung cancer mesothelioma asbestosis (a type of
pneumoconiosis. The trade and use of asbestos have been restricted or
banned in many jurisdictions.
Asbestos is the term used for the fibrous form of a number of
naturally occurring silicate minerals that have been exploited
commercially for their useful properties of:
high tensile strength
low thermal conductivity and
resistance to chemical attack
There are six minerals included in this definition; one,
chrysotile, is in the serpentine group of minerals, while the
others, including amosite, crocidolite, anthophyllite, actinolite
and tremolite belong to the amphibole group of minerals.
TYPES OF ASBESTOS
The three types of asbestos that have found significant
industrial uses are amosite (brown asbestos), chrysotile
(white asbestos) and crocidolite (blue asbestos). None of
these minerals is found in commercial quantities in the
UK, the bulk of the material that were used by industry
were imported from Canada or South Africa.
In total, over 5 million tones of asbestos were imported
into the UK.
The maximum importation of asbestos into the UK
occurred between 1970 and 1975; thereafter importation
has declined and for the amphiboles it has ceased
completely. The figure shows the amount of the three
common types of asbestos imported into the UK during
the last century.
The physical and chemical properties of asbestos determined its
uses and commercial value. The very fine fibers of chrysotile and
crocidolite were ideal for textile products. Their thermal stability
made the asbestos minerals useful in friction products and, together
with their low thermal conductivity, in insulation materials.
Asbestos cements made with chrysotile asbestos were durable
materials because of the chemical bonding of the lime with the
surface of the fibers.
The use of asbestos was banned in Britain in 1999, but there are
still a great deal of asbestos-containing materials in buildings and
Category Mineral Formula
SEM OF ASBESTOS FIBRES
Asbestos fibers (SEM micrograph)
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. 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
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.
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.
IDENTIFICATION AND ASSESSMENT
A fiber cannot be identified or ruled out as asbestos, either using the
naked eye or by simply looking at a fiber under a regular microscope.
The most common methods of identifying asbestos fibers are by
using polarized light microscopy (PLM) or transmission electron
microscopy (TEM). PLM is less expensive, but TEM is more precise
and can be used at lower concentrations of asbestos.
If asbestos abatement is performed, completion of the abatement is
verified using visual confirmation and may also involve air sampling.
Air samples are typically analyzed usingphase contrast microscopy
(PCM). PCM involves counting fibers on a filter using a microscope.
Airborne occupational exposure limits for asbestos are based on using
the PCM method.
The American Conference of Governmental Industrial Hygienists has a
recommended Threshold Limit Value (TLV) for asbestos of 0.1
fibers/mL over an 8 hour shift. OSHA in the United States and
occupational health and safety regulatory jurisdictions in Canada use 0.1
fibers/mL over an 8 hour shift as their exposure limits.
Asbestos can be found naturally in the air outdoors and in some drinkable water,
including water from natural sources. Studies have shown that members of the
general (non-occupationally exposed) population have 10,000-999,999 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.
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 US 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% for every 10 km
(6.2 mi) that an individual had lived away from a likely asbestos source.
Portions of El Dorado County, California are known to contain
natural amphibole asbestos formations at 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 EPA study was refuted by its own peer
reviewers and never completed or published. 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."
However, the main criticism pointed at EPA was that their testing
was conducted in small isolated areas of El Dorado where there were
no amphibole asbestos deposits, thus the language regarding
amphibole, nonfibrous "particles". Actual surface amphibole
deposits in residential areas were ignored for testing purposes.
Because of this, no final findings were published by ATSDR.
A great deal of Fairfax County, Virginia was also found to be
underlaid 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 (150 mm) of clean,
stable material over the ground.
Globally, collected samples from Antarctic ice indicate Chrystoile
asbestos has been a ubiquitous contaminant of the environment for
at least 10,000 years. Snow samples in Japan have shown ambient
background levels are one to two orders of magnitude higher in
urban than in rural areas. Higher concentrations of airborne asbestos
fibers are reported in urban areas where there is more ACM
(asbestos containing materials) and mechanisms of release (vehicles
braking and weathering of asbestos cement materials);
concentrations in the range of 1–20 ng/m^3 have been reported.
Fibers longer than 5μm are rarely found in rural areas. Ambient
concentrations using TEM analysis have been based on mass
HISTORY OF HEALTH CONCERNS AND
The 1st century AD, Greeks and Romans are claimed to have
observed that slaves involved in the weaving of asbestos cloth were
afflicted with a sickness of the lungs,although this is not
confirmed by examination of primary sources.
Early concern in the modern era on 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 in 1898 included a report from Lucy Deane which stated
that asbestos had "easily demonstrated" health risks.
At about the same time, what was probably the first study of
mortality among asbestos workers was reported in France. While
the study describes the cause of death aschalicosis, 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.
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.
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
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, Nellie Kershaw, 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 ..." 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".
Dr. Cooke's second case report was followed, in the late 1920s, 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. 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.
The first known U.S. workers' compensation claim for asbestos disease was in 1927. 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.
In 1930, the major asbestos company Johns-Manville produced a report, for
internal company use only, about medical reports of asbestos worker
fatalities. In 1932, a letter from U.S. Bureau of Mines to asbestos
manufacturer Eagle-Picher stated, in relevant part, "It is now known that
asbestos dust is one of the most dangerous dusts to which man is exposed."
In 1933, Metropolitan Life Insurance Co. doctors found that 29% of workers in a
Johns-Manville plant had asbestosis. Likewise, in 1933, Johns-Manville
officials settled 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." In 1934, officials of two
large asbestos companies, Johns-Manville and Raybestos-Manhattan, edited an
article about the diseases of asbestos workers written by a Metropolitan Life
Insurance Company doctor. The changes downplayed the danger of asbestos
dust. In 1935, officials of Johns-Manville and Raybestos-Manhattan
instructed the editor of Asbestos magazine to publish nothing about
asbestosis. In 1936, a group of asbestos companies agreed to sponsor research
on the health effects of asbestos dust, but required that the companies maintain
complete control over the disclosure of the results.
In 1951, asbestos companies removed all references to cancer before
allowing publication of research they sponsored. In 1952, Dr.
Kenneth Smith, Johns-Manville medical director, recommended
(unsuccessfully) that warning labels be attached to products containing
asbestos. Later, Smith testified: "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."
In 1953, National Gypsum's safety director wrote 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 noted that the letter was "full of
dynamite" and urged that it be retrieved before reaching its destination.
A memo in the files noted that the company "succeeded in stopping" the
letter, which "will be modified."
Through the 1970s, asbestos was used to fireproof roofing and
flooring, for heat insulation, and for a variety of other purposes. The
material was used in fire-check partitioning and doors on North Sea
Oil Production Platforms and Rigs.
During the mid-to late 1980s, public health concern focused on
potential asbestos fiber exposures of building occupants and workers
in buildings containing asbestos containing building materials
(ACBM) and their risks of developing lung cancer or mesothelioma.
As a consequence, the Health Effects Institute (Cambridge, MA)
convened a panel to evaluate the lifetime cancer risk of general
building occupants as well as service workers.
The United States remains one of the few developed countries that hasn't yet fully banned
asbestos. Asbestos is still legal and widely used in such commonly used products like clothing,
pipeline wraps, vinyl floor tiles, millboards, cement pipes, disk brake pads, gaskets and roof
coatings. In 1981, the United States Environmental Protection Agency (EPA) requested
information from American companies regarding the asbestos content of their products.
In 1989 the EPA issued the Asbestos Ban and Phase Out Rule which was subsequently
overturned in the case of Corrosion Proof Fittings v. EPA, 947 F.2d 1201 (5th Cir. 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
In 2010, Washington State banned asbestos in automotive brakes starting in 2014.
The EPA has proposed a concentration limit of seven million fibers per liter of drinking water
for long fibers (lengths greater than or equal to 5 µm). The Occupational Safety and Health
Administration (OSHA), has set limits of 100,000 fibers with lengths greater than or equal to
5 µm per cubic meter of workplace air for eight-hour shifts and 40-hour work weeks.
OSHA regulations regarding asbestos are covered in 29 C.F.R. 1926.1101 (for
construction) and 1910.1001 (for general industry). Such work is divided into four
Class I asbestos work means activities involving the removal of thermal system
insulation and surfacing asbestos containing materials (ACM) and presumed asbestos
containing materials (PACM). Asbestos containing materials are defined by OSHA as
being composed of 1% or more asbestos. Presumed asbestos containing materials are
building materials that are known to have been commonly manufactured using
asbestos, such as floor tiles or thermal system insulation, and were installed before
Class II asbestos work means activities involving the removal of ACM which is not
thermal system insulation or surfacing material. This includes, but is not limited to,
the removal of asbestos-containing wallboard, floor tile and sheeting, roofing and
siding shingles, and construction mastics.
Class III asbestos work means repair and maintenance operations, where "ACM",
including thermal system insulation, as well as surfacing ACM and PACM, is likely
to be disturbed.
Class IV asbestos work means maintenance and custodial activities during which
employees contact, but do not disturb ACM or PACM, as well as activities to clean
up dust, waste and debris resulting from Class I, II, and III activities.
ASBESTOSIS OF THE LUNG
HOW DO FIBRES ENTER THE LUNG?
The speed that fibers settle in air is mainly dependent on their
diameter. Table 1 shows the falling speed of cylindrical fibers
of different diameters.
Table 1 Falling speed of fibers in air diameter (μm) falling
Fibers with diameter less than 3 μm will remain suspended in the air for long enough to reach
deep into the lung. Long thin fibers are just as likely to penetrate into the lungs as short thin ones.
When someone is working with asbestos some of the airborne fibers are inhaled into the lungs,
which comprise a series of branching tubes. The first of these tubes is called the trachea, which is
attached to the larynx. The trachea is about 2 cm in diameter and approximately 12 cm long. The
trachea divides into the left and right bronchi. After a few centimeters these in turn divide into
segmental bronchi and so on with about 25 further sets of branches.
Broader fibers continue to impact in the upper sections of the tracheobronchial tree falling out of
the air stream onto the walls of the bronchial tubes. However, most fibers with diameter less than
3 μm regardless of length, penetrate to the alveolus. This is the part of the lung where gas
exchange between the air and the blood occurs. There are over 200 million alveoli with a total
surface area of more than 100 m2.
Once a fiber has deposited in the lung there is a possibility that it may cause damage to the lung
tissue. This is a condition in which the lung becomes scarred as a result of prolonged inhalation of
asbestos fibers. It only occurs in people exposed to relatively large amounts of asbestos, normally
over many years, such as in milling, weaving, lagging or asbestos removal operations. The
scarring is more properly known as fibrosis. The part of the lung that is damaged is at the far end
of the smallest bronchial tubes, the place where the lung transfers oxygen to the blood stream.
As we have seen, only the finest fibers, less than 3 μm in diameter, are able to reach this part of
the lung. This is why when we come to evaluate the fiber concentration in the air we count only
fibers of this diameter or less.
Once a fiber has deposited in the lung there is a possibility that it
may cause damage to the lung tissue. This is a condition in which
the lung becomes scarred as a result of prolonged inhalation of
asbestos fibers. It only occurs in people exposed to relatively
large amounts of asbestos, normally over many years, such as in
milling, weaving, lagging or asbestos removal operations. The
scarring is more properly known as fibrosis. The part of the lung
that is damaged is at the far end of the smallest bronchial tubes,
the place where the lung transfers oxygen to the blood stream.
As we have seen, only the finest fibers, less than 3 μm in
diameter, are able to reach this part of the lung. This is why when
we come to evaluate the fiber concentration in the air we count
only fibers of this diameter or less.
USES OF ASBESTOS
Chrysotile was by far the most abundant asbestos form in
terms of production and usage (about 93 per cent). It can be
found in a wide variety of products from yarn, rope and
textiles to cement, insulation boards, friction materials,
gaskets and thermoplastics.
Crocidoite had a similar widespread use although the
tendency was to use it in mixtures with other asbestos
varieties. Amosite, because of its coarser nature, tended to
find greater use in asbestos board and other rigid products. All
three varieties may be found in all proportions in old laggings
of pipes and boilers. Crocidoite was little used after about
1970, Amosite after about 1980 and Chrystoile after about
The uses of asbestos in building construction are divided into
ten broad categories:
Spray Coatings and Lagging
Ropes, Yarns and Cloth
Millboard, Paper and Paper Products
Asbestos Cement Products
Bitumen Felts and Coated Metals
Textured Coatings and Paints
Mastic, Sealants, Putties and Adhesives
Bitumen sink pads
Toilet cisterns & seats
Brake Liners/clutch lining
IS ASBESTOS GONE YET?
Because of its association with diseases like mesothelioma
and asbestosis, new uses of asbestos have been banned in the
USA by the Environmental Protection Agency. In October
1991, a U.S. federal court overturned an EPA regulation that
banned most uses of asbestos by 1997. Only products that
were not being manufactured, imported or processed on July
1989 remain subject to the prohibition of asbestos. While
exposure to asbestos has been lowered as a result of abatement
programs, it has recently reared its ugly head in materials that
were never thought to contain asbestos. Vermiculite mined
from Zonolite Mountain in Libby, Montana was found to
contain the asbestos types tremolite and actinolite as well as
four other mineral types (winchite, ricterite, fero-edenite and
magnesioarfvedsonite) that are not on the EPA list of asbestos
minerals, but none the less have all of the properties of
Evidence supports the belief that these "non-asbestos
forms" have resulted in asbestoses and mesothelioma
among mine workers in Libby Montana. In addition,
friable asbestos present in asbestos mined at Libby,
Montana under the name Zonolite may be a health
hazards for nursery workers, installers of popped
vermiculite insulation and individuals living or working
in one of the millions of buildings that contain Zonolite
insulation. Some industrial grade talc has also been
found to contain asbestos. Cosmetic grade talc, on the
other hand, appears to be asbestos free.
In answer to the question "Is asbestos gone?", no, it is not
gone, nor will it ever be gone. Unlike PCBs, DDT and dioxin
asbestos is part of the natural environment. The answer is not
to be totally rid of it, but to maintain a working and living
environment in which airborne asbestos is in a concentration
low enough that it will not result in impaired health or death
from diseases like asbestosis, mesothelioma, etc. When
asbestos is found to be in a state in which it is non- friable and
unlikely to become friable, the present trend is to leave it
alone. Sometimes removal of non-friable asbestos from
buildings can increase rather than decrease the chances for
exposure to friable asbestos. If it is found to be friable
(crumbling and powdery, or of a type that by its very nature is
likely to become airborne), removal is frequently the only
answer. This process must be left to asbestos abatement
Most importantly, asbestos management must also be
controlled at the source. How is it entering industrial and
consumer products? At one time the only pathway
considered to be important in introducing asbestos to our
homes and businesses was via products in which it was
an intentional ingredient. Suddenly it has been found to
be an incidental impurity (as in vermiculite and talc). In
addition, mineral types previously thought to be
unassociated with the asbestos minerals have been found
to have asbestos-like properties. Testing for asbestos at
the source is necessary to limit exposure to workers and
the general public. It will require government, industry
and the general public working together to face the new
challenges of asbestos contamination.
HEARTY THANKS FOR ALL THE INDUSTRIAL ASSOCIATES
WHO HELPED IN THIS INFORMATION COLLECTION
CONTACT US : FRICTIONCOMPOSITES@GMAIL.COM
Next PPT Update : 19 September 2016
Data Source : Wikipedia