Asbestos: Properties, Uses and Problems
1. Introduction
The term asbestos is derived from a Greek word meaning "inextinguishable, unquenchable or inconsumable." It is a generic name for a group of fibrous silicate minerals, the most common of which are chrysotile, crocidolite and amosite. Asbestos is non-flammable even at very high temperatures and is extremely flexible and durable. Asbestos was described in a 1927 doctoral thesis as follows:
"The crude mineral is merely a piece of rock or stone. It has truly been called a physical paradox being both fibrous and crystalline, elastic and brittle, yet able to be carded and so converted as to be spun and woven like wool, flax or silk. It would appear to possess the characters of both vegetable and mineral while being different from either; light and feathery as eiderdown, it is yet as dense and heavy as the rock it resembles... The fiercest heat fails to consume it, nor acids affect the strength of its fibres notwithstanding their delicacy; a strand of it can be spun to weigh less than one ounce per hundred yards length and fine cloth can be made from its fibres weighing only a few ounces to the square yard. Its indestructible nature enables it to resist decay under almost any conditions."
No asbestos is mined in the United Kingdom; the traditional sources of imported raw fibre are Canada and Southern Africa. Throughout the 20th century, over six million tonnes of asbestos were imported.
2. Types of Asbestos
The principal types of asbestos which were used commercially in the UK were: chrysotile, crocidolite and amosite.
2.1 Chrysotile
Also known as white asbestos chrysotile is a member of the Serpentine group, so-named because the fibre is curly. Chrysotile fibres are the most flexible of all asbestos fibres; they can withstand the fiercest heat but are so soft and flexible that they can be spun and woven as easily as cotton. Resistance to alkaline attack makes chrysotile a useful reinforcing material in asbestos-cement building products. Chrysotile was banned in the UK in 1999. Traditionally it was the most widely used of all asbestos types, accounting for approximately 95% of asbestos mined annually. Like the other forms of asbestos, chrysotile can absorb organic materials such as resins and polymers and can be used to strengthen particulates such as cement. In 1994, 5,000 tonnes of chrysotile were imported into the UK; sales of asbestos roofing slates rose by 25% in 1993. Use of asbestos cement products such as corrugated sheet and cavity roof decking, drainage and sewage pipes are acceptable under current regulations. Under similar conditions, products containing chrysotile tend to age better than those containing crocidolite or amosite.
2.2 Crocidolite
Crocidolite is known colloquially as blue asbestos and is a member of the Amphibole group. The needle-like fibres are the strongest of all asbestos fibres and have a high resistance to acids. Crocidolite was used in yarn and rope lagging from the 1880s until the mid 1960s and in preformed thermal insulation from the mid 1920s until 1950. The high bulk volume of crocidolite makes it suitable for use in sprayed insulation; a product which was first manufactured in this country in 1931 at the JWR factory in Armley.
Crocidolite is known to be the most lethal of all the asbestos types. The import of crocidolite peaked in 1950, fell by 25% in 1960 and by 88% in 1970. The "import, supply and use of crude, fibre, flake, powder or waste crocidolite or amosite" wasn't actually banned until the Asbestos (Prohibitions) Regulations of 1985 came into force, although strict guidelines had regulated its use since 1969.
2.3 Amosite
Amosite is also known as brown asbestos and is, like crocidolite, a member of the Amphibole group. Its harsh, spiky fibres have good tensile strength and resistance to heat. In buildings, amosite was used for anti-condensation and acoustic purposes; on structural steel it was used for fire protection. Between the 1920s and the late 1960s amosite was used in preformed thermal insulation, pipes, slabs and moulded pipe fitting covers. In the UK amosite was also used widely in the manufacture of insulation boards. The import of amosite was banned as of 1 January 1986 by The Asbestos (Prohibitions) Regulations 1985.
3. Uses
Asbestos was nicknamed "the magic mineral" because its unique chemical composition and physical properties made it suitable for use in thousands of products from floor tiles to road signs, from sewage pipes to insulating mattresses. Historical records show that asbestos has been used by man for over 4,000 years; in this century it has been used in over 3,000 products including cement building materials, pipework lagging, insulating mattresses and rope, fire resistant insulation boards, sprayed fire-proofing products, floor tiles and coverings, water and sewage pipes, gas masks, friction materials for vehicle brakes and clutches, lifts and machinery. Boilers and pipework were lagged with asbestos products in hospitals, power stations and throughout heavy industry. Asbestos insulation products were popular in the shipbuilding and railway industries and in the dockyards etc. The Royal Yacht Britannia, built in 1952, was riddled with asbestos insulation which was stripped out upon discovery in 1980. Sprayed asbestos insulation containing crocidolite was used in the roof space of the House of Commons Chamber; linings of the ventilation ducts in the House of Commons were insulated with chrysotile (white asbestos).
Asbestos products have been used on a large scale in British buildings for fireproofing, acoustic and thermal insulation, condensation protection and reinforcement in asbestos-cement products. 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. Nearly 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. Other asbestos-containing materials used in British buildings were: sprayed asbestos coatings, asbestos lagging, insulation partition boards, ropes and yarns, cloth, millboard and paper, asbestos cement sheets and partition boards, textured coating, mastics, sealants, putties, adhesives, wall plugging compound, pipework and so on.
4. Problems Arising from Asbestos Usage
On 28 July, 1983 John Gummer, the Under-Secretary of State for Employment, told the House of Commons that asbestos: "is not a substance for which one can set a level below which there is no risk but a substance about which we do not know the lowest level of risk. We must therefore assume that a single fibre could do real damage which may not be seen for 20 years or more." Generally speaking, people with the largest exposure to asbestos have the greatest risk of contracting an asbestos-related disease. The first wave of asbestos disease occurred in workers involved in the mining and milling of crude asbestos and in the manufacture of asbestos products. The second wave affected workers using asbestos products; e.g. insulators, pipe-fitters, construction workers. The third wave is associated with exposure to asbestos in situ; e.g. plumbers, electricians, carpenters and refurbishment workers. In addition para-occupational exposure experienced by relatives of asbestos-contaminated workers is resulting in an increasing number of victims among the wives and children of asbestos workers who brought the dust home on their work clothes. Environmental exposure, such as that experienced by the plaintiffs in the Armley case, has also caused disease.
Products which contain asbestos can generate fibres when they are damaged, disturbed, weathered or old: in these circumstances, fibres are released into the atmosphere and asbestos exposure through respiration can occur. It is widely believed that exposure to asbestos contained in buildings presents a relatively small risk. Nevertheless, the more liable asbestos-containing materials are to be damaged, the higher the health risks. A 1979 government report found that deterioration of sprayed asbestos insulation produced the highest potential risk of fibre release in buildings; high levels of contamination were observed in the presence of abrasive air-movements.
There are no official statistics for the number of British buildings which contain asbestos. The TUC believes that "asbestos is present in most schools and other public buildings erected since the 1960s, especially in walls, ceiling and fire doors, lagging on hot pipes, boilers and ovens and in wall cavities and lofts." According to one industry expert all mature buildings in Britain, that is pre-1980, are liable to contain this category 1 carcinogen. Alan Carneige, a risk manager for insurance advisers Sedgwick UK Ltd., believes that "in any building more than fifteen years old, and in some cases younger, there is likely to be asbestos."
May 2, 2000
