Rate of decline of asbestos fibre concentration in room air

Our plain-English summary of Rate of decline of asbestos fibre concentration in room air, by J.S. Moorcroft, M.J. Duggan (The Annals of Occupational Hygiene, 1984).

The study

• Authors: J.S. Moorcroft, M.J. Duggan
• Journal: The Annals of Occupational Hygiene
• Published: 1984;28(4):453-7
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos fibres may be lost from room air by several mechanisms including gravitational settling, ventilation and attachment to surfaces. The results of some measurements of airborne fibre concentrations obtained during monitoring after the removal of sprayed asbestos ceilings are presented. Some indication is given of the rate at which the concentration of fibres decreases after their having been raised by the disturbance of surface dust. Some theoretical estimates of the losses due to settling and ventilation suggest that these two mechanisms are not sufficient to account for the observed results and that some additional mechanism, possibly attachment to room surfaces, is operative.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

This short communication reported air measurements from classrooms of a North London school whose sprayed amosite ceilings had recently been stripped. The data came from checks on whether the rooms could be re-occupied, not from a study designed for this question. Four rooms were each tested twice, eight tests in all. Each test sampled air with the room undisturbed, then during vigorous dusting, wiping and sweeping, then undisturbed again. Fibres were counted by phase-contrast microscopy. Before disturbance, all levels were below the method's sensitivity limit of 0.01 fibres per ml. Disturbance raised levels in five tests, to between 0.03 and 0.47 fibres per ml. In the other three, levels stayed below 0.01. Afterwards, levels in the five tests fell to between less than 0.01 and 0.04 fibres per ml, reductions of about 2 to 15 times. The authors calculated that settling and ventilation alone could not explain this fall. They suggested fibres may have attached to room surfaces. They concluded that most raised fibres stayed airborne less than 1 hour, so sampling timing may substantially affect results. They noted large counting error at low concentrations.

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: Short communication reporting air-monitoring measurements collected during other work (not a specifically designed study), compared with theoretical calculations of fibre loss
• Who was studied: Four classrooms of a North London school from which sprayed amosite ceilings had recently been stripped; each room tested on two occasions (eight tests). Dates of sampling not given.
• Exposure: Airborne fibres in cleaned rooms after removal of sprayed amosite ceilings, sampled with the room undisturbed, during a vigorous dust disturbance procedure (dusting light fittings, wiping walls and benches, brushing radiators, sweeping), and again undisturbed. Respirable fibres were counted by phase-contrast microscopy.
• Main results:
  • Before disturbance (Period 1), all concentrations in all tests were very low and below the method's sensitivity limit (0.01 fibres per ml).
  • During dust disturbance (Period 2), no increase was seen in Tests 4, 5 and 8 (all values below 0.01 fibres per ml).
  • In Tests 1, 2, 3, 6 and 7, dust disturbance produced a significant increase in fibre concentrations, ranging from 0.03 to 0.47 fibres per ml.
  • In those five tests, concentrations after disturbance (Period 3) fell to between less than 0.01 and 0.04 fibres per ml, reduction factors of about 2 to 15.
  • Fibres sampled during disturbance were mostly fine. Typically less than 25% had a diameter greater than 1 micrometre.
  • By the authors' calculation, gravitational settling alone would reduce concentration by a factor of no more than about two for the fibre sizes measured. Settling combined with an assumed ventilation rate of 0.5 air changes per hour would give a reduction factor of only 2.5 over 1 hour, less than generally observed.
  • The residence time in air of most fibres raised during the measurements was less than 1 hour.
• The authors' conclusion: The authors concluded that settling and ventilation were not sufficient to account for all the observed reductions. They suggested fibres may have been lost by interception with room surfaces, possibly enhanced by static forces. In any sampling procedure that disturbs surfaces to raise fibres, the duration of the disturbance and the timing of sampling may have a substantial effect on the result.
• Limitations the authors state:
  • The measurements were not part of a study designed to investigate fibre decline.
  • Some results carry large experimental error, because counts were low.
  • Phase-contrast microscopy is insensitive at concentrations below 0.01 fibres per ml.
  • Ventilation rates were not measured, only estimated.

Topics

Medical terms in this study, explained in our Lexicon: Settled Dust.

Related studies

• Rate of decline of asbestos fibre concentrations in room air — J. Prentice (1985)
• Comparison of direct and indirect methods of measuring airborne chrysotile fibre concentration — C. Eypert-Blaison, S. Veissiere, et al. (2010)
• Bromo-deoxyuridine (BRDU) uptake in the lungs of rats inhaling amosite asbestos or vitreous fibres at equal airborne fibre concentrations — K. Donaldson, D.M. Brown, et al. (1995)
• The influence of external aerodymanic factors on the measurement of the airborne concentration of asbestos fibres by the membrane filter method — A.M. Johnston, A.D. Jones, et al. (1982)
• Decline in death rates among asbestos insulation workers 1967-1986 associated with diminution of work exposure to asbestos — H. Seidman, I.J. Selikoff (1990)
• Measured removal rates of chrysotile asbestos fibers from air and comparison with theoretical estimates based on gravitational settling and dilution ventilation — J. Sahmel, H.J. Avens, et al. (2015)

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