Asbestos fibers
Encyclopedia
Asbestos
Asbestos
Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...

 fibers (or fibres) are released from asbestos containing materials (ACMs). Friable asbestos containing materials release fibers more readily than encapsulated asbestos containing materials.

Determining airborne asbestos fiber levels

The standard methodology (HSG248 in the UK
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

) for determining airborne asbestos fiber concentration (expressed as fibers per millilitre (fiber/ml) or cubic centimetre (fiber/cm³)) is via the following method:

1. Air pumps are used to suck air through a filter at 8 litres per minute for 60 minutes.

2. The filter is mounted on a slide using acetone
Acetone
Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory...



3. The slide is viewed using either Phase Contrast Microscopy
Phase contrast microscopy
Phase contrast microscopy is an optical microscopy illumination technique of great importance to biologists in which small phase shifts in the light passing through a transparent specimen are converted into amplitude or contrast changes in the image.A phase contrast microscope does not require...

(PCM), Scanning Electron Microscopy(SEM
Scanning electron microscope
A scanning electron microscope is a type of electron microscope that images a sample by scanning it with a high-energy beam of electrons in a raster scan pattern...

), or Transmission Electron Microscopy
Transmission electron microscopy
Transmission electron microscopy is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through...

(TEM
Transmission electron microscopy
Transmission electron microscopy is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through...

). Usually PCM due to cost. A PCM microscope costs approx £2500 GBP.

4. The analyst looks through the microscope and counts the number of objects which meet the HSG248 criteria of potential asbestos fibers. A crowd counter may be used to count fibers per field.

5. The fibers per microscope field are extrapolated to calculate a concentration value (fiber/ml). Unfortunately this is only a "transient index of concentration" rather than an absolute value as the smallest fibers are not visible via PCM.

Comparative exposure levels to airborne asbestos fibers by activity (Fibers per millilitre)

  • Environmental Exposure 0.0001 fiber/ml

  • Rural environmental exposure 0.0001 fiber/ml

  • Urban environmental exposure 0.0001 to 0.001 fiber/ml

  • Environmental exposure downwind from an asbestos
    Asbestos
    Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...

     cement plant at 300 m: 0.0022 fiber/ml

  • Exposure in buildings with friable asbestos
    Asbestos
    Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...

     concentrations 0.001 to 0.01 fiber/ml(counted with an optical microscope)

  • Controlled removal of "Artex
    Artex
    Artex is a surface coating used for interior decorating, most often found on ceilings, which allows the decorator to add a texture to it. The name Artex is a trademark of Artex Ltd., a company based in the UK. The name is a genericised trademark often used to refer to similar products from other...

    " (3% to 5% Chrysotile
    Chrysotile
    Chrysotile or white asbestos is the most commonly encountered form of asbestos, accounting for approximately 95% of the asbestos in place in the United States and a similar proportion in other countries. It is a soft, fibrous silicate mineral in the serpentine group of phyllosilicates; as such, it...

    ) textured decorative coating: 0.08 fiber/ml

  • Vigorous dry scraping for 60 minutes to remove textured decorative plaster from a wall: 0.09 fiber/ml personal sample, estimated PCME

  • Throwing asbestos cement sheets into lorry 0.161 fiber/ml personal

  • "Representative" Asbestos cement roof Removal: Not detected to 0.2 fiber/ml personal

  • "Representative" Asbestos cement roof Repair: Not detected to 0.3 fiber/ml personal

  • Asbestos cement sheets stacked in confined space 0.30 to 0.53 fiber/ml personal

  • Hand sawing asbestos cement sheets and pipes < 1 fiber/ml

  • Careful removal of whole asbestos insulation boards by unscrewing with shadow vacuuming and spray application of a wetting agent on unsealed surfaces: Up to 3 fiber/ml

  • Jig sawing asbestos insulation board with LEV
    Lev
    Lev may refer to:*Lev and LEV are common shortenings for Leviticus, the third book of the Hebrew Bible and of the Torah.*Lev means "heart" in Hebrew.*It is also a Hebrew name, as in the Bar Lev Line....

     1 - 5 fiber/ml

  • Opening raw material Chrysotile
    Chrysotile
    Chrysotile or white asbestos is the most commonly encountered form of asbestos, accounting for approximately 95% of the asbestos in place in the United States and a similar proportion in other countries. It is a soft, fibrous silicate mineral in the serpentine group of phyllosilicates; as such, it...

     from Chongqing
    Chongqing
    Chongqing is a major city in Southwest China and one of the five national central cities of China. Administratively, it is one of the PRC's four direct-controlled municipalities , and the only such municipality in inland China.The municipality was created on 14 March 1997, succeeding the...

    , China
    China
    Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

    , asbestos
    Asbestos
    Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...

     plant 5.8–7.5 fiber/ml

  • Drilling overhead asbestos insulation boards (No LEV
    Lev
    Lev may refer to:*Lev and LEV are common shortenings for Leviticus, the third book of the Hebrew Bible and of the Torah.*Lev means "heart" in Hebrew.*It is also a Hebrew name, as in the Bar Lev Line....

    ): 5 to 10 fiber/ml

  • Hand sawing asbestos insulation board (No LEV
    Lev
    Lev may refer to:*Lev and LEV are common shortenings for Leviticus, the third book of the Hebrew Bible and of the Torah.*Lev means "heart" in Hebrew.*It is also a Hebrew name, as in the Bar Lev Line....

    ): 5 to 10 fiber/ml

  • Jig sawing asbestos insulation board (No LEV
    Lev
    Lev may refer to:*Lev and LEV are common shortenings for Leviticus, the third book of the Hebrew Bible and of the Torah.*Lev means "heart" in Hebrew.*It is also a Hebrew name, as in the Bar Lev Line....

    ): 5 to 20 fiber/ml

  • Breaking and ripping out asbestos insulation boards dry with no unscrewing: 5 to 20 fiber/ml

  • Abrasive disc cutting of asbestos cement sheets and pipes without LEV
    Lev
    Lev may refer to:*Lev and LEV are common shortenings for Leviticus, the third book of the Hebrew Bible and of the Torah.*Lev means "heart" in Hebrew.*It is also a Hebrew name, as in the Bar Lev Line....

     15 to 25 fiber/ml

  • Bagging raw material Chrysotile
    Chrysotile
    Chrysotile or white asbestos is the most commonly encountered form of asbestos, accounting for approximately 95% of the asbestos in place in the United States and a similar proportion in other countries. It is a soft, fibrous silicate mineral in the serpentine group of phyllosilicates; as such, it...

     in Chongqing
    Chongqing
    Chongqing is a major city in Southwest China and one of the five national central cities of China. Administratively, it is one of the PRC's four direct-controlled municipalities , and the only such municipality in inland China.The municipality was created on 14 March 1997, succeeding the...

    , China
    China
    Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

    , asbestos
    Asbestos
    Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...

     plant (1999) 5.2–58.4 fiber/ml

  • Sweeping asbestos insulation board debris up to 10 fiber/ml

  • Dry removal of asbestos lagging up to 100 fiber/ml

  • Dry removal of sprayed (limpet) coating up to 1000 fiber/ml

Rate of decline of asbestos fiber concentration in room air

Airborne asbestos fibers settle very slowly and in relation to their diameter.

A 3 micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...

diameter fiber is estimated to settle at 150 millimetres per minute.

However a 0.5 micrometre diameter fiber is estimated to settle at 4 millimetres per minute.

Thus the time for a fiber to fall 2 metres is:
  • 3 micrometre fiber: 13 minutes
  • 0.5 micrometre: 8 hours

Further reading

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