A study of the size distributions of airborne amosite fibres in the manufacture of asbestos insulation boards

Our plain-English summary of A study of the size distributions of airborne amosite fibres in the manufacture of asbestos insulation boards, by S.T. Beckett, J.L. Jarvis (The Annals of Occupational Hygiene, 1979).

The study

• Authors: S.T. Beckett, J.L. Jarvis
• Journal: The Annals of Occupational Hygiene
• Published: 1979;22(3):273-84
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A comparison has been made of the size distributions of airborne fibres at different locations in two major manufacturing plants using amosite asbestos. Side-by-side samples were taken on membrane and Nuclepore filters; the membrane filters were examined using optical phase microscopy and the length distributions of fibres longer than 5 µm measured. The Nuclepore filter samples were examined using scanning electron microscopy and the lengths of fibres greater than 0.6 µm with diameters of more than 0.2 µm were determined. No major differences were found in size distribution either at the different sites or due to the analytical technique used, except for samples taken in relatively high velocity air streams. The effect of a change from the present standard in length or aspect ratio of the fibres counted on the measured concentration is discussed.

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

In plain English

This study measured the sizes of airborne amosite asbestos fibres in two British insulation board factories, at Uxbridge and Glasgow. The authors took 25 pairs of side-by-side air samples at tasks such as bag opening, sawing and sanding, and in general areas. One filter of each pair was examined by optical phase contrast microscopy and the other by scanning electron microscopy (SEM). Fibre length distributions did not differ significantly between most locations. The exceptions were four static samples taken in relatively high-velocity air streams. The two methods gave closely matching length distributions for most samples of fibres longer than 5 micrometres. At 500 times magnification, the optical count averaged 1.7 times the SEM count. When the SEM magnification was raised to 1000 times, the SEM count was 1.15 times the optical count at the lower magnification, a difference that was not significant. Fibres longer than 5 micrometres numbered about twice those longer than 10 micrometres. Changing the length-to-width ratio counting rule from 3:1 to 5:1 affected only 1% of fibres longer than 5 micrometres. The authors concluded that the optical fibre count appears to be a valid technique for monitoring the longer asbestos fibres.

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: Workplace air-sampling measurement study comparing fibre size distributions between locations and between two microscopy methods: optical phase contrast microscopy on membrane filters and scanning electron microscopy on Nuclepore filters, using side-by-side samples
• Who was studied: Air samples from two British plants making amosite asbestos insulation board, at Uxbridge and Glasgow. There were 25 pairs of samples, static and personal, from production, sanding, sawing, bag opening, dust extraction and warehouse areas. Further samples came from UICC amosite in an animal inhalation chamber and from six extra filters near a high-velocity extraction system.
• Exposure: Airborne amosite asbestos fibres generated during wet board-making, cutting, sawing, sanding, bag opening, dust extraction and handling of finished boards
• Main results:
  • Optical measurements at Uxbridge: there was no significant difference between 8 general-environment locations. Samples from bag opening and one sanding operation had a higher proportion of longer fibres (p < 0.001).
  • Glasgow: samples near a sander and in an enclosed area had significantly different lengths (p < 0.001) from the other 13 positions, with a smaller proportion of longer fibres.
  • All four differing distributions were static samples taken in relatively high-velocity air streams.
  • The mean length distributions in the general environment of the two factories did not differ significantly.
  • Very close agreement was found between SEM and optical microscope length distributions for most samples of fibres longer than 5 micrometres. The two outlying locations were the exceptions.
  • At 500 times magnification, the optical count averaged 1.7 times the SEM count (p < 0.001).
  • With the SEM at 1000 times magnification, the SEM count was 1.15 times the optical count at the lower magnification. This difference was not significant.
  • The count of fibres longer than 5 micrometres was approximately twice the count of fibres longer than 10 micrometres.
  • Raising the aspect ratio from 3:1 to 5:1 affected only 1% of fibres longer than 5 micrometres, and would reduce the count of fibres longer than 0.6 micrometres by 7%.
  • A 10:1 aspect ratio would have meant 9% fewer fibres longer than 5 micrometres and a 34% reduction in the count of fibres longer than 0.6 micrometres.
  • Four UK laboratories sized six circulated optical slides, and overall no significant difference was found between the laboratories.
  • Samples from 1973 and 1976 at the same factories had similar length distributions, giving no strong evidence of large changes since 1973.
• The authors' conclusion: The authors concluded that length distributions did not differ significantly between most locations in the two plants. They found the optical microscope was not preferentially missing long, very fine fibres, and that the optical fibre count appears to be a valid technique for monitoring the longer asbestos fibres. They called for further work on high-velocity airstreams and for wider exchanges of SEM samples between laboratories.
• Limitations the authors state:
  • Diameter distributions were less exact than length measurements, because many fibres had diameters close to the microscope's limit of resolution.
  • The cause of the difference between optical and SEM results in high-velocity airstreams was not established.
  • Because of expense and limited instrument time, only three electron microscope samples were exchanged with other laboratories.
  • The earlier (1973 and 1976) samples were analysed by a different operator on another SEM, which may explain their slightly higher proportion of shorter fibres.
  • In one exchanged SEM sample, longer fibres were probably lost during transport.

Topics

Medical terms in this study, explained in our Lexicon: Amosite, Scanning Electron Microscopy (SEM), Aspect Ratio (Length-to-diameter ratio).

Related studies

• Size distributions of occupational airborne asbestos textile fibres as determined by transmission electron microscopy — A.P. Rood, R.R. Streeter (1984)
• Airborne brake wear debris: size distributions, composition, and a comparison of dynamometer and vehicle tests — P.G. Sanders, N. Xu, et al. (2003)
• Airborne fiber concentration and size distribution of mineral fibers in area with serpentinite outcrops in Aichi prefecture, Japan — K. Sakai, N. Hisanaga, et al. (2001)
• 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)
• The dimensions of airborne asbestos fibres--I. Crocidolite from Kuruman area, Cape Province, South Africa — C.Y. Hwang, G.W. Gibbs (1981)
• Development of a fibre size-specific job-exposure matrix for airborne asbestos fibres — J.M. Dement, E.D. Kuempel, et al. (2008)

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