Asbestos (Some facts)

What is "asbestos" ?

" The term asbestos designates a group of naturally occurring fibrous serpentine or amphibole minerals that have extraordinary tensile strength, conduct heat poorly and are relatively resistant to chemical attack. The principal varieties of asbestos are chrysotile, a serpentine mineral, and crocidolite, amosite, anthophyllite, tremolite and actinolite, all of which are amphiboles."

As asbestos travel in the air, these borderless travelers can be inhaled inside human body via breathing system which can cause severe health problems as such cancer because they are much less soluble in

lung fluids, and they have long residence times in the lungs. In addition, asbestos can also be found in food and drink but we will  limit ourselves to discuss the impact of this substaince on human by inhaling.

There are two main sources of asbestos: natural sources such as rock formation which emits to the air by  natural weathering and can be enhanced by man's activities but this type of source is not as significant as man-made sources that are from mining and milling, manufacturing of products, construction activities, transport and use of asbestos-containing products and disposal.

According to World Health Organization Air Quality Guidelines,  indoor asbestos fibers concentration can be considerably higher than outdoor concentrations because it originates from insulation material sprayed on steelwork or ceilings (such material may become highly friable after some years),  asbestos plaster, low-weight insulation plates, etc. Sometimes such materials have been used in direct or close contact with air-conditioning equipment. It is said that under certain assumption, assuming a breathing rate of 10 m3 for an 8-hour working day and 200 working days per years, a worker inhales 2000 m3 per year during working hours while the total inhalation for the general population is 7300 m3 per year for the outdoor working environment. On the other hand,  with the US finding of indoor fiber concentration the average values range from 400 F/m3 to 500 F/m3, which results in a lifetime fiber burden of up to 200 000 000 F/m3.

 Measurement unit:

• Fiber/ml (the unit of fibers per mililiter)
• F/m3 (Fibers per m3) 
  

Characteristics of asbestos:

• larger or equal to 5 micrometer with up to 3 micrometer diameter. 
• the settling rate of airborne asbestos is relative to their diameter (eg. 3 micrometer at speed 150 mm per minute in room air)
  

 References:

http://en.wikipedia.org/wiki/Asbestos_fibers#cite_note-manchester-7.

http://www.euro.who.int/document/aiq/6_2_asbestos.pdf  (World Health Organisation Air Quality Guidelines Second Edition (2000), WHO Regional Office for Europe, Copenhagen, Denmark).