Asbestos fibers are released from asbestos containing materials (ACMs). Friable asbestos containing materials release fibers more readily than encapsulated asbestos containing materials. [edit] Determining airborne asbestos fiber levels The standard methodology(MDHS100 in the UK) 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
3. The slide is viewed using either Phase Contrast Microscopy(PCM), Scanning Electron Microscopy(SEM), or Transmission Electron Microscopy(TEM). 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 MDHS 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. [edit] Comparative exposure levels to airborne asbestos fibers by activity (Fibers per millilitre) - Environmental Exposure 0.0001 fiber/ml[1]
- Rural environmental exposure 0.0001 fiber/ml[2]
- Urban environmental exposure 0.0001 to 0.001 fiber/ml[2]
- Environmental exposure downwind from an asbestos cement plant at 300 m: 0.0022 fiber/ml[2]
- Exposure in buildings with friable asbestos concentrations 0.001 to 0.01 fiber/ml(counted with an optical microscope)[2]
- Controlled removal of "Artex" (3% to 5% Chrysotile) textured decorative coating: 0.08 fiber/ml[3]
- Vigorous dry scraping for 60 minutes to remove textured decorative plaster from a wall: 0.09 fiber/ml personal sample, estimated PCME[4]
- Throwing asbestos cement sheets into lorry 0.161 fiber/ml personal[5]
- "Representative" Asbestos cement roof Removal: Not detected to 0.2 fiber/ml personal[6]
- "Representative" Asbestos cement roof Repair: Not detected to 0.3 fiber/ml personal[6]
- Asbestos cement sheets stacked in confined space 0.30 to 0.53 fiber/ml personal[7]
- Hand sawing asbestos cement sheets and pipes < 1 fiber/ml [8]
- 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[8]
- Jig sawing asbestos insulation board with LEV 1 - 5 fiber/ml [8]
- Drilling overhead asbestos insulation boards (No LEV): 5 to 10 fiber/ml [8]
- Hand sawing asbestos insulation board (No LEV): 5 to 10 fiber/ml [8]
- Jig sawing asbestos insulation board (No LEV): 5 to 20 fiber/ml [8]
- Breaking and ripping out asbestos insulation boards dry with no unscrewing: 5 to 20 fiber/ml [8]
- Abrasive disc cutting of asbestos cement sheets and pipes without LEV 15 to 25 fiber/ml [8]
- Sweeping asbestos insulation board debris up to 10 fiber/ml[10]
- Dry removal of asbestos lagging up to 100 fiber/ml[10]
- Dry removal of sprayed (limpet) coating up to 1000 fiber/ml[10]
[edit] 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 diameter fiber is estimated to settle at 150 millimetres per minute.[11]
However a 0.5 micrometre diameter fiber is estimated to settle at 4 millimetres per minute.[11]
Thus the time for a fiber to fall 2 metres is: - 3 micrometre fiber: 13 minutes
- 0.5 micrometre: 8 hours
[edit] References - ^ J. Peto, C. Rake, C. Gilham, A. Darnton & J. Hodgson, (October 2006), "Observations and speculations on mesothelioma risks and asbestos exposure in Britain", BOHS Autumn meeting, Manchester, UK
- ^ a b c d World Health Organisation Air Quality Guidelines Second Edition (2000), WHO Regional Office for Europe, Copenhagen, Denmark
- ^ G. Burdett (Nov 2005), "Airborne fiber concentration during the removal of asbestos containing textured decorative plasters and paints and the risk to workers Report Number IFS/05/13", UK Health and Safety Laboratory
- ^ Burdett, GJ & Scott, R (1988) "Fibre Release from Chrysotile-containing Decorative Plasters" UK HSE/RLSD Report No: IR.L/DI/88/03
- ^ Preat, B. (1993), Surveillance de Chantiers avec Fibres-Ciment. Instituut voor Reddingswezen, Ergonomie en Arbeidshygiene, Hasselt, Belgium; Report Ref. 2240-F.
- ^ a b CONSAD Research Corporation (1990). "Economic analysis of the proposed revisions to the OSHA asbestos standard for construction and general Industry. OSHA J-9-8-0033, U.S. Dept. of Labor, Washington, DC
- ^ Brown, S.K. (1987), Asbestos Exposure During Renovation and Demolition of Asbestos-Cement Clad Buildings, Am. Ind. Hyg. Assoc. J. 48 (5): 478-486.
- ^ a b c d e f g h Manchester Metropolitan University (2000), "HEALTH AND SAFETY ASBESTOS GENERAL GUIDANCE"
- ^ a b E.Yano, Z.Wang, X.Wang, M.Wang, Y.Lan (2001) "Cancer Mortality among Workers Exposed to Amphibole-free Chrysotile Asbestos", American Journal of Epidemiology, Vol. 154, No. 6
- ^ a b c North Cornwall District Council Asbestos Policy (2005)
- ^ a b J. S. MOORCROFT and M. J. DUGGAN (1984) "RATE OF DECLINE OF ASBESTOS FIBER CONCENTRATION IN ROOM AIR", Environmental Sciences Division, Scientific Services Branch, Greater London Council, London SE1 7PB, U.K.
[edit] Further reading |
