When mined and processed, asbestos
is typically separated into very thin fibers.
Asbestos fibers are stronger than steel and
quite resilient, making the stone appealing
for a wide range of industrial applications.
Yet the strength and resilience of asbestos
also make it dangerous to human health. When
these fibers are present in the air, they are
normally invisible to the naked eye. Because
these fibers are so small and light, they may
remain in the air for many hours if they are
released from asbestos containing materials
in a building. Asbestos fibers can penetrate
bodily tissue, particularly the lungs, eventually
causing tumors to develop.
History
The word asbestos is derived
from a Greek adjective meaning inextinguishable.
The "miracle mineral" as it was referred
to by the Greeks, was admired for 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 the
flames of a fire.
From the time of the Greeks
and Romans in the first century until its re-emergence
in the eighteenth cnetury, asbestos received
little attention or use. It was not available
in large amounts until extensive deposits were
discovered in Canada in the nineteenth century
(late 1800's). By the late nineteenth century,
asbestos was coming to be used in a variety
of textile products and, increasingly, to insulate
boilers, steam pipes, turbines, ovens, kilns,
and other high temperature equipment.
Properties
of Asbestos
Generally, asbestos fibers
are long, thin, strong, fireproof, flexible,
and resistant to the action of many chemicals.
Chrysotile, the most common asbestos type, is
usually white or off white, with long wavy fibers.
In some mines, the fibers are exceedingly long
and flexible, making this chrysotile excellent
for weaving into fire and heat resistant cloth.
Shorter chrysotile fibers were more apt to be
used as binders and strengtheners in plastics,
cement or insulation.
Amosite is usually brown or
tan, with much straighter and fibers than chrysotile.
Amosite was the second most commonly used type
of asbestos, comprising approximately 5%of the
asbestos placed in buildings and factories.
Crocidolite is a fairly rare
form of asbestos, unique because of its very
obvious blue color. Crocidolite fibers appear
long and straight, much like Amosite.
The remaining three asbestos
types were not extensively used in commercial
products in the United States.
Asbestos
Uses
Asbestos fibers have been used
in many different applications in our industrialized
society. The most common uses of asbestos have
been:
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- Thermal and acoustic insulation
- Fireproofing
- Textiles
- Asbestos – concrete
- Plastic products (vinyl floor
tiles)
- Paper products
- Gasket, packaging
- Roofing felts, papers
- Electrical
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In the United States, commercial
use of asbestos began in the early 1900’s and
peaked in the period from World War II into the
1970’s. Under the Clean Air Act of 1970 the Environmental
Protection Agency (EPA) began regulating many
asbestos-containing materials which, by EPA definition,
are materials with more than 1- percent asbestos.
Health Effects
It is now clear that exposure
to airborne asbestos fibers can cause disease.
The risk of developing asbestos-related disease
varies according to the intensity, duration and
nature of the exposure.
Asbestos exposure can cause a
number of disabling and fatal diseases. The principal
route of exposure is by inhalation through the
nose and mouth. Asbestos, traditionally valued
for its indestructibility, is especially resistant
to the internal defenses of the human body. Once
lodged inside the lungs, most fibers will not
break up or dissolve. They can’t be neutralized
or removed.
ASBESTOSIS is a disease
that is characterized by pulmonary fibrosis, a
progressive scarring of the lung caused by the
accumulation of asbestos fibers. Asbestosis is
associated exclusively with chronic, occupational
exposure. The build up of scar tissue interferes
with oxygen uptake through the lungs and can lead
to respiratory and heart failure. Often, asbestosis
is a progressive disease, even in the absence
of continued exposure. Symptoms include shortness
of breath, cough, fatigue, and vague feelings
of sickness. When the fibrosis worsens, shortness
of breath occurs even at rest.
LUNG CANCER is a malignant
tumor of the bronchi covering. The tumor grows
through surrounding tissue invading and often
obstructing the air passages. The earliest symptom
is often a persistent cough; a physical exam may
attribute the symptom of chronic bronchitis. Chest
x-rays sometimes show shadows that indicate tumors
and enlarged lymph nodes. However, the definitive
diagnosis of lung cancer is based upon microscopic
examination of lung tissue. The time between exposure
to asbestos and the occurrence of lung cancer,
is 20-30 years. There is no threshold or limit
of exposure below which the risk of lung cancer
is not increased.
MESOTHELIOMA is a cancer
of the mesothelium, the lining of the chest or
the lining of the abdominal wall. Early stages
are associated with few symptoms. By the time
it is diagnosed, it is almost always fatal. Effective
therapy does not exist. There is no exposure threshold
for mesothelioma. This is suggested by the observation
that family members of asbestos-exposed workers
have developed mesothelioma. Presumably cleaning
the clothes of the exposed worker has exposed
these individuals to asbestos dust and led to
the disease. Similar to other asbestos- related
diseases, mesothelioma has an extended latency
period of 30 to 40 years.
PLEURAL PLAQUES and PLEURAL
CALCIFICATION are markers of exposure and
may develop 10 to 20 years after initial exposure.
Plaques are opaque patches visible on chest x-rays
that consist of dense strands of connective tissue
surrounded by cells. All commercial types of asbestos
induce plaques. Plaques can occur even when fibrosis
is absent and do not seem to reflect the severity
of pulmonary disease.
OTHER DISEASES and adverse
health effects have been noted among the population
exposed to asbestos fibers. Increased incidences
of non-respiratory cancers have been observed
in some recent epidemiological studies. Cancers
of the larynx, esophagus, stomach, colon-rectum,
kidney and pancreas are present at slightly higher
than predicted levels.
Other substances appear to cooperate
with asbestos to multiply the risk of lung cancer.
People who smoke 20 cigarettes per day increase
their risk of developing lung cancer by ten-fold
(10X) when compared to non-smoker. Workers exposed
to the same level of asbestos as insulation workers
historically increase their risk of developing
lung cancer by five-fold (5X). These two factors
working together have a synergistic effect; the
smoker exposed to asbestos fibers is at least
fifty times (50X) more likely to develop lung
cancer than the general public.
