الأربعاء، 25 سبتمبر 2013
Asbestos is a set of six naturally appearing silicate minerals used commercially for their desirable physical properties
Their names are
- actinolite
- amosite
- chrysotile
- anthophyllite
- crocidolite
- tremolite
The principal forms of asbestos are white asbestos (chrysotile) and blue asbestos (crocidolite).
Crocidolite and amosite are the most dangerous of the asbestos minerals set because of their long persistence in the lungs of exposed people. Chrysotile is often contaminated with tremolite asbestos, thus creating an additional hazard. Chrysotile asbestos, can produced tumors in animals, like all other forms of asbestos minerals.
Asbestos crystals structure, make him
different from most other crystalline minerals. Asbestos crystals
become flexible, long, silky fibres, so it can be made into a wide
variety of forms. Because it is resistant of high temperatures, his
extraordinary tensile strength, and relative resistance to chemical
attack, asbestos is used commercially for insulation in buildings and as
an ingredient in a number of products, such as fire blankets, medical
packing, plastic fillers, roofing shingles, and water supply lines, as
well as clutches and brake linings, gaskets and pads in automotive industry.
In nature asbestos can be found in the air outdoors, indoors and in some drinkable water, including water from natural sources. Actual indoor and outdoor concentrations in the air range from below one hundred to several thousand fibres per m3.
Why is asbestos a serious problem - Asbestos and Health?
Raw asbestos crystals will split into individual fibers which are large enough to be seen, but they can split even further into microscopic fibers. These small fibers are flying in the air, and can even pass through some respiratory dust filters.
Why is asbestos a serious problem - Asbestos and Health?
Raw asbestos crystals will split into individual fibers which are large enough to be seen, but they can split even further into microscopic fibers. These small fibers are flying in the air, and can even pass through some respiratory dust filters.
When asbestos fibres are inhaled , they may cause scars in the lung tissue, cancer of the bronchial tree (lung cancer) and sometimes cancer in the pleura and peritoneum. If asbestos fibers are inhaled in a high concentration over a long time period of time it is more likely to cause some serious health problems. This is most common among asbestos miners, because these workers have the longest exposure to it.
To humans, all
forms of asbestos are carcinogenic, and may cause mesothelioma, lung
cancer, larynx and ovary cancer. Asbestos exposure is also responsible
for other diseases, such as pleural plaques, asbestosis, thickening and
effusions.
Patients who become ill from inhaling asbestos fibers are often those who are exposed on a day-to-day basis in a job where they worked directly with the asbestos materials. As a person's exposure to fibers increases, then that person's risk of the disease also increases,
because of being exposed to higher concentrations of fibers and/or by
being exposed for a longer time. Mesothelioma cancer and other asbestos related diseases are very unlikely to result from a short period of exposure to lower levels or from a single, high-level exposure.
Mesotheliomas have been observed on people who were occupationally exposed to white asbestos (chrysotile), population
who lived close to asbestos mines and factories, and family members of
the occupationally exposed. According to the NCI, "A history of asbestos
exposure at work is reported in about 70 percent to 80 percent of all
cases. Asbestosis has been reported primarily in asbestos workers, and
appears to require exposure to a high concentration over a long time
period for the development of the clinical disease. There is also a long
latency period of over 12 years. Some studies have shown an increased risk of lung cancer among smokers who are exposed to asbestos compared to nonsmokers.
Health Canada states that the asbestos content of a product does not indicate its health risk. Asbestos is hazardous to health only when asbestos fibres are in the air that people breathe.
The evidence that ingested asbestos causes gastrointestinal or other cancers is insufficiently proven.
The carcinogenic properties of asbestos are most probably due to its
fibre geometry and remarkable integrity; other fibres with the same
characteristics may also be carcinogenic.
Current
environmental concentrations of asbestos are not considered a hazard
with respect to asbestosis. A risk of mesothelioma and lung cancer from
the current concentrations can't be excluded.
Studies also shown
that members of the 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 in millions of fibers and
tens of thousands of asbestos bodies in every person's lungs. Health
risks associated with exposure to NOA (naturally occurring asbestos) are
not yet fully understood, and current US federal regulations do not
address exposure from NOA.
Has the use of asbestos containing products changed during the years?
After
it became evident that regular exposure to asbestos products on the job
involved health risks, the public became more concerned about exposure
to asbestos in offices and schools, and, eventually, about all asbestos
products. This concern has led to a dramatic decline in asbestos
products use since the early 1980s. The use of asbestos insulation products in heating systems and buildings has practically disappeared. Using asbestos products for roofing, appliances and flooring, also continues to decrease.
Today Hazardous Products Act regulates the sale of asbestos containing products. Asbestos is now better closed and sealed to reduce the escape of fibres. Asbestos is still valuable
in many applications because it has been difficult to find comparable
substitute materials. For example, it is an important component of
clutch facings and brake lining.
