Asbestos

Asbestos is a group of six naturally occuring minerals made up of heat resistant fibres. Asbestos fibres do not dissolve in water or evaporate, they are resisttant to heat, fire, chemical and biological degradation and are mechanically strong.

Introduction

Asbestos was widely used in construction as an effective insulator, and it can be added to cloth, paper, cement, plastic and other materials to make them stronger. Yet when asbestos dust is inhaled or ingested, the fibres can become permanently trapped in the body. Over decades, trapped asbestos fibres can cause inflammation, scarring and eventually genetic damage. Exposure to asbestos can cause cancer and other health conditions. A rare and aggressive cancer called mesothelioma is almost exclusively caused by asbestos exposure. Asbestos also causes a progressive lung disease called asbestosis.

Although asbestos comes from all over the world, the main exporters are Russia, Kazakhstan and China and it was once mined throughout North America. Asbestos may be found in large deposits or as contaminates in other minerals such as talc and vermiculite. Chrysotile asbestos is usually found as veins within serpentine rock. While most commercial asbestos deposits contain 5% to 6% asbestos, some deposits, such as the Coalinga deposit in California, contain 50% or more asbestos.

Asbestos is generally divided into two sub-groups; serpentine and amphiboles. Serpentine asbestos (chrysotile or white asbestos) was the most commonly used type of asbestos. Chrysotile asbestos fibres are soft, flexible and curved and far less hazardous than the amphibole type. Amphibole fibres (crocidolite -blue asbestos, amosite- brown asbestos, tremolite, actinolite and anthophyllite) are brittle fibres and are often rod- or needle-like in appearance. It is this form that is more hazardous to health. Crocidolite was the most commonly used amphibole asbestos in the past.

The importation, supply and use of all asbestos has been banned in the UK since 1999; the amhibole type has been banned since 1985. Prior to use being banned, asbestos was used in many products including insulation material for buildings, boilers and pipes, car brakes, floor tiles and in 'artex' wall and ceiling decoration.

Types of Asbestos

There are six mineral tyoes of asbestos and these are split into two main clasees of asbestos:

Serpentine - Serpentine class fibres are curly in appearance. There is only one member in this class of asbestos, called Chrysotile.

• Chrysotile asbestos is obtained from serpentine rocks, which are found commonly throughout the world. Chrysotile appears under the microscope as a white fibre. This type of asbestos has been used more than any other, as it is more flexible than any of the Amphibole class asbestos and can be spun and woven into a fabric. Its most common use has been in corrugated asbestos cement roof sheets typically used for outbuildings, warehouses and garages. It may also be found in sheets or panels used for ceilings and sometimes for walls and floors. Chrysotile has been a component in joint compounds and some wall plaster. Numerous other items have been made containing chrysotile, including brake linings, fire barriers in fuse boxes, pipe insulation, floor tiles, and gaskets for high temperature equipment.

Amphibole - Amphibole class fibres are needle-like in form. the remaining five types of asbestos fall into this category including Crocidolite, Amosite, Tremosite, Anthophyllite and Actinolite.

• Crocidolite asbestos is the fibrous form of the amphibole riebeckite. Crocidolite is seen under the microscope as a blue fibre. Often referred to as blue asbestos, it is considered the most hazardous. In 1964, Dr Christopher Wagner discovered an association between blue asbestos and the asbestos related cancer mesothelioma. Unbelievably, Bolivian-mined crocidolite was used in Kent Micronite cigarette filters in the 1950s. Blue asbestos was also formerly used in early gas masks