The descent angle of inclined cylinders--a possible means of separating fibres by length

Our plain-English summary of The descent angle of inclined cylinders--a possible means of separating fibres by length, by T.L. Ogden, W.H. Walton (The Annals of Occupational Hygiene, 1975).

The study

• Authors: T.L. Ogden, W.H. Walton
• Journal: The Annals of Occupational Hygiene
• Published: 1975;18(2):157-60
• Read it: PubMed · Publisher

In plain English

This short laboratory paper from the Institute of Occupational Medicine, Edinburgh, explored a possible way to sort fibres by length for inhalation or injection experiments. The authors noted this is hard to do because a fibre's fall speed depends mainly on its diameter. A tilted cylinder falling slowly does not fall straight down, and the authors calculated this "descent angle" from a 1911 theory by Gans. The calculated angle depended partly on the length-to-diameter ratio, reaching about 19.5 degrees for an infinitely long shape. To check the theory, the authors dropped pieces of copper wire with length-to-diameter ratios of 3 or 20 through glycerol and photographed their fall. The measured angles agreed with the theory for these moderate ratios. No asbestos fibres were tested. By calculation, the authors judged that natural fibres, even amphiboles, would usually be too uneven to keep a steady tilt. The authors concluded that, combined with sorting by diameter, the method could give length-separated respirable fibres. They added that asbestos would probably need magnetic alignment (Timbrell's method) and glass fibre might not, and that the method might be difficult in practice.

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: Laboratory physics experiment testing a theoretical calculation (Gans' theory) of how tilted cylinders fall in viscous fluid
• Who was studied: Cylinders cut from tinned copper wire (diameter 0.549 mm), with length-diameter ratios of 3 or 20, dropped in glycerol in a glass tank; no asbestos fibres, animals or people
• Exposure: No health exposure was studied. The paper concerns a possible method for producing length-sorted respirable fibres for inhalation or injection experiments.
• Main results:
  • Calculated from theory: the descent angle varied with length-diameter ratio, up to about 19.5 degrees for an infinitely long ellipsoid tilted at about 55 degrees
  • Measured angles for the copper wire cylinders agreed with the theory, at least for the moderate length-diameter ratios tested
  • The authors estimated that a fibre's mass being off-centre by 1% of its length would change its tilt by 90 degrees within about twenty lengths of fall
  • The authors judged that natural fibres, even amphiboles, would usually be too asymmetrical to keep a constant tilt
  • For asbestos fibres falling in air, the authors reasoned that the theory should apply to fibres small enough to enter the lung
• The authors' conclusion: The authors concluded that Gans' theory satisfactorily predicts the descent angle of cylinders of moderate length-diameter ratio. Combined with separation by diameter, this could give a way to collect respirable fibre separated by length. Asbestos would probably need Timbrell's magnetic alignment method, while glass fibre might be classified without it.
• Limitations the authors state:
  • Separation by descent angle is possible in principle but might be difficult in practice
  • End effects could make the ellipsoid approximation break down for cylinders with low length-diameter ratio

Related studies

• Conversion of the asbestos fibre concentration recorded by means of the konimeter and the thermal precipitator to that expected by means of the membrane filter method — R.S. du Toit, T.C. Gilfillan (1979)
• Significance of fibre length in the clearance of asbestos fibres from the lung — A. Morgan, R.J. Talbot, et al. (1978)
• Asbestos-stimulated tumour necrosis factor release from alveolar macrophages depends on fibre length and opsonization — K. Donaldson, X.Y. Li, et al. (1992)
• Fibrogenesis by mineral fibres: an in-vitro study of the roles of the macrophage and fibre length — M. Aalto, A.G. Heppleston (1984)
• Asbestos fibre length-dependent detachment injury to alveolar epithelial cells in vitro: role of a fibronectin-binding receptor — K. Donaldson, B.G. Miller, et al. (1993)
• Reaction of cells cultured in vitro to different asbestos dusts of equal surface area but different fibre length — J.L. Kaw, F. Tilkes, et al. (1982)

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