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What Is Asbestos?

General Definition

Asbestos is the name of a group of highly fibrous minerals with separable, long, and thin fibers. Separated asbestos fibers are strong enough and flexible enough to be spun and woven. Asbestos fibers are heat resistant, making them useful for many industrial purposes. Because of their durability, asbestos fibers that get into lung tissue will remain for long periods of time.

For more information on asbestos, see ATSDR's Toxicological Profile on Asbestos. Other ATSDR resources include the Public Health Statement on Asbestos, which is the summary chapter from the Toxicological Profile, and the ToxFAQs for Asbestos, which is a shorter question and answer version.

Types of Asbestos

There are two general types of asbestos, amphibole and chrysotile. Some studies show that amphibole fibers stay in the lungs longer than crystotile, and this tendency may account for their increased toxicity (harmfulness to the body).

asbestiform amphibole

Scanning electron micrograph of asbestiform amphibole from a former vermiculite mining site near Libby, Montana. Source: U.S. Geological Survey and U.S. Environmental Protection Agency, Region 8, Denver, Colorado.

Regulatory agencies such as the U.S. Environmental Protection Agency (EPA) and Occupational Safety and Health Administration (OSHA) recognize six asbestos minerals: chrysotile, a serpentine mineral with long and flexible fibers; and five amphibole (with relatively brittle crystalline fibers) minerals, actinolite asbestos, tremolite asbestos, anthophyllite asbestos, crocidolite asbestos, and amosite asbestos.  

How Are People Exposed to Asbestos?

We are all exposed to low levels of asbestos in the air. These "ambient" - or typical - air concentrations of asbestos fibers are 0.00001 to 0.0001 fibers per milliliter (fiber/mL). Much more concentrated levels of exposure are known to cause health effects in humans. For more information on asbestos exposure, see the Public Health Statement on Asbestos, "How might I be exposed to asbestos?"

Asbestos Exposure and Your Work

Asbestos exposure can occur in the workplace, particularly if you work or have worked as a(n):

  • Pipe or Steam Fitter
  • Plumber
  • Brake Repair Mechanic
  • Insulation Installer
  • Dry Wall Finisher
  • Carpenter
  • Roofer
  • Electrician
  • Welder
  • Miner
  • Shipyard Worker

Individuals who have worked in the above industries should consult with a physician with expertise in the evaluation and management of asbestos-related lung disease.

Chrysotile Asbestos Exposure

The asbestos fibers detected in the samples taken at the World Trade Center sites were chrysotile asbestos.

Amphibole Asbestos Exposure

  • Mining activities

    Exposure to tremolite asbestos (a type of amphibole asbestos) can occur in workers involved in mining, milling, and handling of other ores and rocks containing tremolite asbestos (such as vermiculite or talc).  Residents who live near mining, milling, or manufacturing sites that involve tremolite asbestos-containing material may be exposed to higher levels of airborne asbestos.
A vermiculite mine

A vermiculite mine in Libby, Montana. Asbestos has been detected in vermiculite from this mine.


  • Insulation and Building Materials

    Amphibole asbestos can be found in a variety of building materials, such as insulation, ceiling or floor tiles, and cement pipes. Amphibole asbestos has been found in some vermiculite sources used as home and building insulation. Much of the asbestos-contaminated vermiculite mined in Libby, Montana, was used to produce attic insulation products.

Bagged Asbestos Waste

Bagged asbestos awaits disposal in a landfill.


Workers or homeowners involved in demolition work, maintenance, repair, or remodeling of buildings containing these products can be exposed to higher airborne fibrous amphibole levels than levels in ambient air. However, exposure can occur only when materials containing asbestos are disturbed in some way to release fibers into the air. When asbestos-containing materials are solidly embedded or contained, exposure risk will be minimal.

ATSDR, in conjunction with the EPA recently published a brochure which identifies potential health hazards posed by asbestos in certain building insulation products. The brochure provides information on how to identify these products and steps individuals can take to reduce exposure. Also, see ATSDRs Vermiculite Consumer Products Fact Sheet.

  • Consumer Products

    Vermiculite was also commonly sold in gardening and hardware stores. It was used as a soil amendment (conditioner to improve soil quality) or fertilizer carrier, and it was an ingredient in many potting soil mixtures.

    In addition, small amounts of amphibole asbestos have been found in some talc-containing crayons. The Consumer Product Safety Commission (CPSC) concluded that the risk is extremely low that children would be exposed to asbestos fibers in crayons. The U.S. manufacturers of these crayons, however, have agreed to eliminate talc from their products.

Detecting Asbestos

The combined use of detection methods called light microscopy, electron microscopy, and energy dispersive X-ray analysis offer the most accurate approach to identify asbestos and to estimate concentrations that may become airborne upon disturbance. For the purposes of counting asbestos fibers in these samples, regulatory agencies commonly count as fibers those particles of asbestos minerals at least 5 micrometers in length and with length: width ratios of 3:1. For other purposes, such as detecting fibers in bulk building materials, asbestos particles with length: width ratios of 5:1 are counted. Air concentrations of asbestos fibers in ambient (typical) air are 0.00001 to 0.0001 fibers per milliliter (fiber/mL). The recently established exposure limit for U.S. workplaces is 0.1 fiber/mL.

For your convenience, we have prepared  a list of search terms used in order of popularity, to find more pages on this subject:

Searches completed in January 2005 

Count Search Term 

52264 asbestos 
13457 asbestos cancer 
11725 asbestos cancer lung 
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5074 asbestos removal 
4611 asbestos mesothelioma 
3398 asbestos attorney 
2578 asbestos exposure 
2322 asbestos litigation 
2046 asbestos testing 
1916 abatement asbestos 
1669 asbestos disease 
1579 asbestos tile 
1447 asbestos survey 
1440 asbestos legislation 
1339 asbestos siding 
1335 asbestos firm law 
1189 asbestos settlement 
1109 asbestos lawsuit 
1004 asbestos bill 

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