Asbestos refers to a small number of minerals that are formed of flexible fibers, and have the useful physical property of being very heat resistant.  Because asbestos forms as flexible fibers it can be woven to make fabrics for heat-resistant and insulating materials.  Being able to weave such a material allows it to be used in a great many products.  Unfortunately, this usefulness is undermined by asbestos' deadly properties.

Asbestos is a group of six metamorphic minerals of the hydrous magnesium silicate variety:

• Chrysotile asbestos
• Tremolite asbestos
• Actinolite asbestos
• Anthophyllite asbestos
• Crocidolite asbestos
• Amosite asbestos

Asbestos occurs naturally in many forms; it is mined from metamorphic rocks.  When asbestos is used for its resistance to fire or heat, the fibers are often mixed with cement or woven into fabric or mats.

Asbestos is used in brake shoes and gaskets for its heat resistance, and in the past was used on electric oven and hotplate wiring for its electrical insulation at elevated temperature, and in buildings for its flame-retardant and insulating properties, tensile strength, flexibility, and resistance to chemicals.

The inhalation of some kinds of asbestos fibers, however, causes various serious illnesses, including cancer.

Thus, most uses of asbestos are banned in many countries.  Fiberglass has been found to be a suitable substitute for thermal insulation, and woven ceramic fiber performs as well as or better than asbestos as an insulator of high-temperature electrical conductors.

Most respirable asbestos fibers are invisible to the unaided human eye because their size is about 3.0-20.0 µm (micrometers) 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. Thus, 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 over and over until they have been broken down to their smallest unit dimensions.

For this reason, one larger asbestos fiber can ultimately become the source of hundreds of much thinner and smaller fibers in a normal environment over the course of time.

As they get smaller and lighter, they become more mobile and more easily entrained (wafted) into the air, where human respiratory exposures typically result.

The released fibers being heavier than air will eventually settle in quiescent conditions only to be resuspended over and over again by any kind of activity or air currents over a period of time. This cyclic re-entrainment has consequences.

Consistent with the tenets of the Second Law of Thermodynamics, the smallest sizes of easily mobile asbestos fibers move away from their initial source location in an ever-broadening manner.

They disperse both by simple spontaneous airborne diffusion and through mass transport of the fibers. This latter is an energy-driven process that can occur through directed air currents or by "pickup and release" along a pathway of directed movement by persons, mechanical equipment or vehicles.  In other words, these deadly fibers can be carried home by workers on their clothing and in their hair.

For these reasons, asbestos contamination does not tend to remain localized at its initial release point but will eventually spread throughout all available accessible areas of buildings, even into areas that don't have their own asbestos-containing products.

Eventually asbestos from virtually all products that were manufactured from this mineral will invade each and every space within an affected building. This is because during the lifecycle of each asbestos product, microscopic fibers and larger particles or pieces of these products are typically produced during their residency.

The lifecycle of an asbestos containing product begins from the initial delivery of the product to the building, followed by its installation, normal usage forces, age-related deterioration, physical or chemical damage that often occurs, to finally its removal either for replacement or demolition.

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 which then add to the pool of similar fibers and particles from other asbestos containing products within that building.

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. But non-friable asbestos containing materials are not necessarily safe.

The forces or conditions of usage that come into intimate contact with most non-friable asbestos containing materials are substantially higher than finger pressure.

Because of this, non-friable asbestos products can and do release substantial quantities of free asbestos fibers into their environments as well.

During normal usage, initially non-friable products slowly change into a quasi-friable condition. Asphalt asbestos floor tiles are typically worn down through a sanding action of the normal floor grit under foot traffic on such floor coverings.

Asbestos shingles, siding and roofing materials are eroded through drying, weathering, embrittlement, acid rain leaching and other deteriorative changes to their binder matrix resulting in release of asbestos fibers ("chalk dust") when simple contact is made with their surface or when the wind blows across them.

NCI Fact Sheet

The National Cancer Institute has a fact sheet on asbestos in question and answer format.

The History of Asbestos

See our information sheet detailing the interesting and long history of asbestos.

Carbon Nanotubes May Act Like Asbestos

Carbon Nanotubes are one of the most interesting new materials being researed.  Like asbestos they have many useful properties, and like asbestos, they many cause very severe diseases.