Indoor asbestos levels on a housing estate (determined by transmission electron microscopy)

Our plain-English summary of Indoor asbestos levels on a housing estate (determined by transmission electron microscopy), by D. Gazzi, G.W. Crockford (The Annals of Occupational Hygiene, 1987).

The study

• Authors: D. Gazzi, G.W. Crockford
• Journal: The Annals of Occupational Hygiene
• Published: 1987;31(4A):429-39
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

In plain English

This study measured airborne asbestos fibres inside occupied flats on an estate of about 1400 flats built in the early 1970s with Asbestolux asbestos insulating board, which contains amosite and chrysotile. Between March and June 1983, air was sampled in 25 of these flats and in five control flats on a nearby estate built without asbestos materials. Asbestos fibres longer than 5 micrometres were counted by transmission electron microscopy. Asbestos was found in 48% of samples from the asbestos-containing flats and in none from the control flats. A one-sided statistical test gave P = 0.06, just short of conventional significance, which the authors attributed to too few samples. The time-weighted average in the asbestos-containing flats was 2.8 x 10^-4 fibres per ml (95% confidence limits 1.6 x 10^-4 to 4.5 x 10^-4). In the control flats it was below 1.4 x 10^-4. The highest single concentration was 0.003 fibres per ml. About three-quarters of the asbestos fibres found were amosite. The authors concluded that such board can be a source of airborne fibres, and that optical microscopy is unsuitable for measuring these low levels.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Indoor air-sampling survey comparing flats containing asbestos board with control flats without known asbestos, using transmission electron microscopy
• Who was studied: 25 Local Authority flats with Asbestolux board (out of 32 selected, 78% response) on an estate of about 1400 CLASP-system flats built in the early 1970s, and 5 control flats (out of 10 selected, 50% response) on a nearby estate built without asbestos materials. The flats chosen had two to four bedrooms and families of more than one generation. Sampling ran from 18 March 1983 to 20 June 1983.
• Exposure: Asbestolux asbestos insulating board containing amosite and chrysotile, located around and inside airing cupboards, on kitchen or hallway walls, and over service ducts. Only asbestos fibres longer than 5 micrometres, thinner than 3 micrometres, with length at least three times width, were counted.
• Main results:
  • 48% of the samples from the asbestos-containing flats contained asbestos fibres.
  • No asbestos fibres were found in the samples from the five control flats.
  • Fisher's exact one-sided test comparing how often asbestos fibres were found in asbestos-containing flats versus control flats gave P = 0.06, which the authors said just fails to reach the conventional level of statistical significance.
  • There appeared to be no association between the visually inspected condition of the Asbestolux boards and airborne asbestos levels in the flats.
  • The highest concentration measured in any flat was 0.003 fibres per ml.
  • The time-weighted average airborne asbestos fibre concentration in the asbestos-containing flats was 2.8 x 10^-4 fibres per ml (95% confidence limits 1.6 x 10^-4 to 4.5 x 10^-4).
  • In the asbestos-free control flats the level was below 1.4 x 10^-4 fibres per ml.
  • About three-quarters of the asbestos fibres found in the asbestos-containing flats were amosite rather than chrysotile. The authors took this as strong evidence that the Asbestolux boards were the source.
  • 77% of the chrysotile fibres and 45% of the amosite fibres had diameters of 0.3 micrometres or below, which is below the normal resolving power of the optical (phase contrast) method.
  • Well over half the particles with a length-to-width ratio above 3:1 were not asbestos fibres. The authors said this demonstrates the limits of optical microscopy for measuring low asbestos levels.
  • The lower limit of sensitivity of the counting method was 0.002 fibres per ml, based on a count of eight fibres.
  • The average level in the asbestos-containing flats was considerably lower than the value of 0.001 fibres per ml quoted by Doll and Peto (1985). The authors described it as an order of magnitude below that level.
• The authors' conclusion: The authors concluded that the fibre levels found in dwellings containing asbestos board indicate that such board can be a source of airborne fibres. They added that the levels were low, and that optical microscopy methods are unsuitable for studying fibre levels in domestic buildings.
• Limitations the authors state:
  • The authors attributed the failure of the comparison between asbestos-containing and control flats to reach statistical significance to an insufficient number of samples.
  • The authors stated that electron microscope counts cannot be related to optical (phase contrast) counts unless both methods are used on parallel samples.

Topics

Medical terms in this study, explained in our Lexicon: Transmission Electron Microscopy (TEM).

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