Types of Asbestos
Asbestos is a naturally occurring fibrous mineral product that is strong, durable and non combustible. There are six minerals defined as asbestos. These are: chrysotile (White), amosite (Brown), crocidolite (Blue), tremolite, anthophyllite and actinolite. The three main types of asbestos which have been commercially used are chrysotile (White), amosite (Brown), crocidolite (Blue).
However, these three types of asbestos cannot be identified by colour alone since the addition of chemicals or heat can change their appearance. The fibres are very fine and mostly invisible to the naked eye and when disturbed can float around in the atmosphere being easily breathed in, causing potentially lethal illnesses. All types of asbestos are dangerous but blue and brown are generally more dangerous than white. Asbestos was, and still is commercially mined in Canada, South Africa and Russia.
Chrysotile is also known as white asbestos and is obtained from Serpentine rocks and it is so-named as the fibres are curly. Chrysotile fibres are the most flexible of all asbestos fibres and their resistance to alkaline attack makes chrysotile a useful reinforcing material. It is more flexible than amphibole types of asbestos and can be spun and woven into fabric.
The most common use is within corrugated asbestos cement roof sheets typically used for outbuildings, warehouses and garages. It is also found as flat sheets used for ceilings and sometimes for walls. Numerous other items have been made containing chrysotile including brake linings, cloth behind fuses (for fire protection), pipe insulation, in floor tiles and in rope seals to boilers.
According to The Final Report of the Advisory Committee on Asbestos, the use of chrysotile (white asbestos) was by far the most widespread in Britain. As an example, almost 40% of the chrysotile imported into Britain in 1976 was incorporated into asbestos cement building products, 22% was used in fillers and reinforced cements and 12% went into floor tiles and flooring. Chrysotile has traditionally been the most widely used of all asbestos types, accounting for approximately 95% of asbestos mined annually. The import and use of chrysotile was banned in the UK in 1999.
Amosite asbestos is more commonly referred to as ‘brown’ asbestos and is, like crocidolite (blue asbestos), a member of the Amphibole group. It was found and is mined in South Africa, although some is also found in Australia. It is considered to be one of the more hazardous forms of the material and is naturally more hazardous than serpentine (e.g. white) asbestos, and second only to blue asbestos.
Its harsh, spiky fibres have good tensile strength and resistance to heat. For these reasons amosite asbestos was, at one time, the second most prevalent type of asbestos found in building materials, accounting for about 5% of all asbestos used in factories and other commercial buildings. It is found mainly in building materials and, in the UK, was used primarily as a fire retardant in thermal insulation products, such as ceiling tiles. This form of asbestos is highly friable, which means it crumbles easily when damaged, therefore releasing airborne fibres that can then be inhaled by those in the vicinity of the material.
The import, supply and use of crude, fibre, flake, powder or waste amosite wasn’t actually banned until the Asbestos (Prohibitions) Regulations of 1985 came into force, although strict guidelines had regulated its use since 1969.
Crocidolite is known blue asbestos and is a member of the Amphibole family. It was traditionally mined in South Africa, Bolivia, and Western Australia.
Crocidolite fibres are finely textured and hair-like, occurring in naturally formed bundles, and are long and straight, like amosite. These straight, needle-like fibres are easy to inhale and will remain in the lungs indefinitely. These fibres are the strongest of all asbestos fibres, have a high resistance to acid and are less brittle than brown asbestos fibres.
The high bulk volume of crocidolite makes it suitable for use in sprayed insulation, such as asbestos-cement products. Crocidolite is known to be the most lethal of all the asbestos types. Indeed, crocidolite is the most hazardous of the amphibole asbestos family. No longer mined, blue asbestos was proven to be much less heat resistant than some of the other types, specifically chrysotile. which is why its uses were limited and did not include applications like insulation.