Asbestos is a fibrous inorganic mineral material widely used in building and HVAC insulation and other building materials in the middle of the last century. It was banned in the 1970's and an intensive removal effort has occurred. About 20% of buildings in the US have some type of friable asbestos containing material in them. A material containing asbestos is called friable when the material can be crumbled, pulverized, or reduced to a powder in the hand.
The U.S. Department of Health, Education and Welfare reported that in 20 U.S. cities, airborne asbestos concentrations ranged up to 0.007 fibres per cubic centimeter (fibres/cc) and averaged 0.0006 fibres/cc. The National Academy of Sciences concluded that the average outside air concentration throughout the United States is 0.0004 fibres/cc.
Asbestos causes asbestosis, or fibrosis of the lungs, sometimes leading to cancer. It also causes cancer of the larynx and is suspected of causing cancer of the gastrointestinal tract. It is generally people who have been exposed to high concentrations of asbestos fibers in the air who develop serious health effects from their exposure.
Asbestos is contained in the following materials:
| Product type | Purpose | Generally found |
| Acoustical | Sound control | Ceilings in classrooms, halls, multi-purpose rooms |
| Thermal insulation | Safety-energy conservation | Pipes and boilers |
| Steel fireproofing | Fire protection | Covering structural steel |
| Asbestos cement board | Fire protection | Near furnaces and boilers |
| Tile and sheet flooring | Cleanability-decor | Floors, classrooms and halls |
| Textiles | Fire protection | Auditorium curtains, laboratory aprons and gloves |
Asbestos is generally not considered dangerous unless fibers of asbestos from the material containing the asbestos are released into the air. Dry applied materials are often in the category which can release fibers. In many cases the asbestos is covered with a sealed covering to reduce or eliminate the release of fibers into the air.