Definition
Asbestos roof tiles and roofing sheets are fibre cement products manufactured with chrysotile (white asbestos) fibers bonded in Portland cement, typically at 10–15% asbestos by weight. Used extensively in residential, agricultural, and industrial construction from the 1930s through the mid-1980s, they were sold under trade names including Eternit, Everite, and Asbestolux, among others. When weathered or undamaged, asbestos cement roofing is classified as non-friable — the fibers are firmly bonded in the cement matrix. However, mechanical damage, weathering, algae and moss growth, or cutting and drilling can release fibers. Friable surface material can also wash off with rainwater, potentially contaminating soil and guttering below. Before removing, cutting, or pressure-washing asbestos cement roofing, the material should be confirmed by laboratory analysis. In most countries, removal must be carried out by a certified or licensed contractor, and the waste disposed of at a licensed asbestos waste facility.
See also:
ACM (Asbestos-Containing Material)
ACM (asbestos-containing material) is any material with more than 1% asbestos by weight. At peak use, ACMs appeared in over 3,000 different products: insulation, fireproofing materials, roofing, flooring, and cement products. Buildings must be surveyed for ACMs before renovation or demolition, and any found must be managed or removed to protect occupants and workers.
Non-Friable Asbestos
Asbestos-containing material that is bonded or encapsulated in a cement, resin, or other binding material, making it difficult to crumble by hand when dry. Examples include asbestos cement sheets, floor tiles, and roofing materials. While considered less hazardous than friable asbestos when undisturbed, it can become friable through weathering, water damage, or mechanical damage.
Chrysotile (White Asbestos)
The most commonly used type of asbestos (CAS 12001-29-5), accounting for approximately 95% of asbestos found in buildings. Chrysotile is a serpentine mineral with curly fibers, also known as white asbestos. While historically considered less dangerous than amphibole asbestos, it is now recognized as carcinogenic and capable of causing mesothelioma and other asbestos-related diseases. Note: chrysotile should not be confused with chrysolite, a synonym for the mineral olivine (a completely different silicate). The similarity has caused persistent errors in print since at least 1909, when mineralogist John W. Evans proposed reviving the original Greek name karystiolite (from καρύστιος λίθος, "Karystian stone"), after the town of Karystos in Euboea, Greece, where fibrous serpentine was quarried in antiquity, the same stone Pliny called marmor carystium.
Asbestos Insulation
Asbestos insulation refers to any thermal, acoustic, or fire-resistant insulation material that contains asbestos fibers. It was applied in several distinct forms, each with a different risk profile. Spray-applied insulation (the highest-hazard type, 50–85% asbestos by weight) was sprayed onto structural steelwork, ceilings, and walls for fire protection; it is highly friable and can shed fibers without deliberate disturbance. Pipe lagging and boiler insulation (pre-formed sections wrapped around hot pipes, tanks, ducts, and boilers) commonly used chrysotile, amosite, or crocidolite; in poor condition, it presents high exposure risks for maintenance workers. Loose-fill insulation (blown into wall cavities and roof spaces) is extremely friable once disturbed. Rope and blanket insulation was used around industrial equipment and furnaces. The asbestos type varied by product and era — chrysotile, amosite, and crocidolite were all used in different insulation products. Asbestos insulation, particularly spray-applied and loose-fill forms, is subject to the most stringent assessment and removal requirements under most national regulations.