Asbestos in Modern Usage

Serpentine group

Chrysotile is the form of asbestos from the serpentine group that has been used commercially.

In the United States, chrysotile has been the most commonly used type of asbestos. Chrysotile is often present in a wide variety of materials, including but not limited to:

* sheetrock taping
* mud and texture coats
* vinyl floor tiles, sheeting, adhesives and ceiling tiles
* plasters and stuccos
* roofing tars, felts, siding, and shingles
* "transite" panels, siding, countertops, and pipes
* acoustical ceilings
* fireproofing
* putty
* caulk
* gaskets
* brake pads and shoes
* clutch plates
* stage curtains
* fire blankets


Amphibole group

Amosite and crocidolite were used in many products until the early 1980s. The use of all types of asbestos in the amphibole group was banned in the mid-1980s. 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)

Asbestos as a contaminant

Asbestos is in the air we breathe and some of the water we drink, including water from natural sources. Studies have shown that members of the general (nonoccupationally 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.

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). 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.

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.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, they more easily become airborne and human respiratory exposures can result.Fibers will eventually settle but may be re-suspended by air currents or other movement.

Asbestos does not tend to remain localized at its initial release point and may eventually spread throughout all available accessible areas of buildings, even into areas that don't have their own asbestos-containing products. Any small impact or damage to a typical asbestos containing product can easily release billions to trillions of fibers of asbestos into the immediate environment.

Friability of an asbestos containing product 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 asbestos containing materials are substantially higher than finger pressure. Non-friable asbestos products can release substantial quantities of asbestos fibers into their environments as well.

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