The term Asbestos describes six types of non-conductive, fibrous minerals made of silica. All contain the element magnesium, and some also contain calcium and iron. Valued for its fire-proof characteristics, tensile strength and chemical resistance, asbestos was a superstar material used worldwide in building construction and industrial environments in the twentieth century.
Now, use of these minerals is severely restricted. Many countries including Australia have banned asbestos entirely. The once coveted material is a known carcinogen, and has caused thousands of Australians to contract the cancer known as mesothelioma or die of asbestosis and fatal lung diseases.
Nature of Asbestos
In its natural state, asbestos does not look like any other rock. One form, chrysotile, contains bundles of long white crystal filaments, clearly visible in the raw ore and resembling fine linen or flax threads. These threads are the reason for both its industrial benefits and its cancerous nature.
To give an idea of how small asbestos fibres are, consider that a human hair is one tenth of a millimeter or 100 microns wide. Compare this to the average diameter of a strand of asbestos, about 0.5 microns in diameter or 200 times smaller than a human hair. Not only are the filaments very small, they also can separate into microscopic fragments. When inhaled, these fragments can travel deep into the lungs where the body cannot expel them. Over time, sometimes decades, deadly diseases develop.
Types of Asbestos
Early names for asbestos included “wooly stone” and “cotton rock.” Fibers may be:
- Long, silky, and curled, known as serpentine-type asbestos, which can be woven into cloth. It is the most common variety, and is used most often to strengthen cement products. This type of asbestos is known as white chrysotile. Blue crocidolite also possesses long fibres, and was used in sprayed-on insulation.
- Short, needle-like fibers, added to clay for stronger pottery in ancient cultures. A recent and popular use added asbestos to cement products. Varieties include actinolite, tremolite, anthophyllite, and amosite. Brown amosite became the material of choice for ceiling tiles and insulating heated pipes.
Friable vs. Non-Friable
The health risks associated with asbestos depend on how the mineral is handled and incorporated into products. Some applications sprayed asbestos coatings onto surfaces, which did not change its friable, easily crushed nature. Asbestos is most dangerous when in dust form, which facilitates becoming airborne and inhaled. Examples of friable products are sprayed on insulation, some types of plaster, and ceiling tiles.
Asbestos added to materials like asphalt, cement, or vinyl is contained and considered a safe form unless disturbed. Products are solid, non-friable substrates that will not produce hazardous dust unless broken, cut or abraded in some way. Examples of non-friable asbestos products are vinyl floor tiles, cement roofing sheets and asphalt roof tiles.
Although when left alone these asbestos products are considered safe, natural disasters such as the tornado in Lennox Head, NSW in June of 2010 shakes that superficial confidence. Homes made of "fibro" were damaged in a tornado, exposing large areas to asbestos fibres.
Mining and Industry
When asbestos is excavated, the rock formations break apart and fibers are released into the air, a deadly hazard to the miners. Naturally occurring deposits of asbestos have been mined and used in Australia for over one hundred years. Mining was executed by hand in some outback regions like Baryulgil, requiring miners to manually extract fibres by pulling them out of the ore.
Asbestos products had humble beginnings as a curiosity, with textiles such as purses, tablecloths, napkins, and blankets. Adding the minerals to cement and insulation propelled asbestos manufacture into high gear, supplying contractors with building materials and aiding the war effort with fire proofing, sound dampening, and cheap, efficient insulation on board ships.
Twentieth century applications of asbestos included fire-resistant materials, sprayed-on fireproofing for walls and ceilings, cement reinforcement, auto parts resistant to heat from friction, wall board, insulation, talc, ceiling and floor tiles, roofing, and construction materials. Workers are exposed to sources of these fibrous materials in activities such as auto assembly and repair, roofing, ship building, cement product manufacture, mining, building construction, and demolition. Diseases caused by inhalation of asbestos fibres include the cancer mesothelioma, asbestosis, and lung diseases classified as pneumoconiosis.
For more information on the hazards, health risks and liabilities of asbestos in your home or work place, contact Asbestos Audits International.
Asbestos and Other Fibrous Materials: Mineralogy, Crystal Chemistry and Health Effects; H.C.W. Skinner, M. Ross, C. Frondel, Oxford University Press, 1988.
OSHA Fact Sheet:
A Brief Guide to Asbestos in Emergencies,: Safer Handling and Breaking the Cycle
Shelter Center, ProAct Network, Environmental Partnerships for Community Resilience. 2006 Available for download from www.proactnetwork.org or www.sheltercenter.org