Abstract

A laser light-scattering instrument has been designed to facilitate the real-time detection of potentially hazardous respirable fibers, such as asbestos, within an ambient environment. The instrument captures data relating to the spatial distribution of light scattered by individual particles in flow by use of a dedicated multielement photodiode detector array. These data are subsequently processed with an artificial neural network that has previously been trained to recognize those features or patterns within the light-scattering distribution that may be characteristic of the specific particle types being sought, such as, for example, crocidolite or chrysotile asbestos fibers. Each particle is thus classified into one of a limited set of classes based on its light-scattering properties, and from the accumulated data a particle concentration figure for each class may be produced and updated at regular intervals. Particle analysis rates in excess of 103/s within a sample volume flow rate of 1 l/min are achievable, offering the possibility of detecting fiber concentrations at the recommended maximum exposure limit of 0.1 fibers/ml within a sampling period of a few seconds.

© 1997 Optical Society of America

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References

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  1. R. C. Brown, J. A. Hoskins, N. F. Johnson, eds. , Mechanisms in Fiber Carcinogenesis, Life Science, Vol. 223 (Plenum, New York, 1991), pp. 1–589.
  2. J. Peto, J. T. Hodgson, F. E. Matthews, J. R. Jones, “Continuing increase in mesothelioma mortality in Britain,” Lancet 345, 535–539 (1995).
    [CrossRef] [PubMed]
  3. Testimony of NIOSH on occupational exposure to asbestos, tremolite, anthrophyllite, and actinolite. 29CFR, Parts 1910 and 1926, 9 May 1990.
  4. J. Carter, D. Taylor, P. A. Baron, “Fibers method 7400 revision no. 3:5/15/89” in NIOSH Manual of Analytic Methods (U.S. Department of Health and Human Services, Washington, D.C., 1989).
  5. P. Lilienfeld, P. Elterman, P. Baron, “Development of a prototype fibrous aerosol monitor,” Am. Ind. Hyg. Assoc. J. 40, (4), 270–282 (1979).
    [CrossRef] [PubMed]
  6. P. A. Baron, M. K. Mazumder, Y. S. Cheng, “Direct reading techniques using optical particle detection,” in Aerosol Measurement, K. Willeke, P. A. Baron, eds. (Reinhold, New York, 1993), pp. 403–408.
  7. A. P. Rood, E. J. Walker, D. Moore, “Construction of a portable fibre monitor measuring the differential light scattering from aligned fibres,” in Proceedings of the International Symposium: Clean Air at Work, R. H. Brown, M. Curtis, K. J. Saunders, S. Vandrendreissche, eds. (Royal Society of Chemistry, London, 1992), pp. 265–267.
  8. E. Hirst, P. H. Kaye, J. Guppy, “Light scattering from non-spherical airborne particles: experimental and theoretical comparisons,” Appl. Opt. 33, 7180–7186 (1994).
    [CrossRef] [PubMed]
  9. P. H. Kaye, K. Alexander-Buckley, E. Hirst, S. Saunders “A real-time monitoring system for airborne particle shape and size analysis,” J. Geophys. Res. 101, 19,215–19,221 (1996).
    [CrossRef]
  10. R. O. Duda, P. E. Hart, Pattern Classification and Scene Analysis (Wiley, New York, 1973).
  11. C. F. Bohren, D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley, New York, 1983).

1996 (1)

P. H. Kaye, K. Alexander-Buckley, E. Hirst, S. Saunders “A real-time monitoring system for airborne particle shape and size analysis,” J. Geophys. Res. 101, 19,215–19,221 (1996).
[CrossRef]

1995 (1)

J. Peto, J. T. Hodgson, F. E. Matthews, J. R. Jones, “Continuing increase in mesothelioma mortality in Britain,” Lancet 345, 535–539 (1995).
[CrossRef] [PubMed]

1994 (1)

1979 (1)

P. Lilienfeld, P. Elterman, P. Baron, “Development of a prototype fibrous aerosol monitor,” Am. Ind. Hyg. Assoc. J. 40, (4), 270–282 (1979).
[CrossRef] [PubMed]

Alexander-Buckley, K.

P. H. Kaye, K. Alexander-Buckley, E. Hirst, S. Saunders “A real-time monitoring system for airborne particle shape and size analysis,” J. Geophys. Res. 101, 19,215–19,221 (1996).
[CrossRef]

Baron, P.

P. Lilienfeld, P. Elterman, P. Baron, “Development of a prototype fibrous aerosol monitor,” Am. Ind. Hyg. Assoc. J. 40, (4), 270–282 (1979).
[CrossRef] [PubMed]

Baron, P. A.

P. A. Baron, M. K. Mazumder, Y. S. Cheng, “Direct reading techniques using optical particle detection,” in Aerosol Measurement, K. Willeke, P. A. Baron, eds. (Reinhold, New York, 1993), pp. 403–408.

J. Carter, D. Taylor, P. A. Baron, “Fibers method 7400 revision no. 3:5/15/89” in NIOSH Manual of Analytic Methods (U.S. Department of Health and Human Services, Washington, D.C., 1989).

Bohren, C. F.

C. F. Bohren, D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley, New York, 1983).

Carter, J.

J. Carter, D. Taylor, P. A. Baron, “Fibers method 7400 revision no. 3:5/15/89” in NIOSH Manual of Analytic Methods (U.S. Department of Health and Human Services, Washington, D.C., 1989).

Cheng, Y. S.

P. A. Baron, M. K. Mazumder, Y. S. Cheng, “Direct reading techniques using optical particle detection,” in Aerosol Measurement, K. Willeke, P. A. Baron, eds. (Reinhold, New York, 1993), pp. 403–408.

Duda, R. O.

R. O. Duda, P. E. Hart, Pattern Classification and Scene Analysis (Wiley, New York, 1973).

Elterman, P.

P. Lilienfeld, P. Elterman, P. Baron, “Development of a prototype fibrous aerosol monitor,” Am. Ind. Hyg. Assoc. J. 40, (4), 270–282 (1979).
[CrossRef] [PubMed]

Guppy, J.

Hart, P. E.

R. O. Duda, P. E. Hart, Pattern Classification and Scene Analysis (Wiley, New York, 1973).

Hirst, E.

P. H. Kaye, K. Alexander-Buckley, E. Hirst, S. Saunders “A real-time monitoring system for airborne particle shape and size analysis,” J. Geophys. Res. 101, 19,215–19,221 (1996).
[CrossRef]

E. Hirst, P. H. Kaye, J. Guppy, “Light scattering from non-spherical airborne particles: experimental and theoretical comparisons,” Appl. Opt. 33, 7180–7186 (1994).
[CrossRef] [PubMed]

Hodgson, J. T.

J. Peto, J. T. Hodgson, F. E. Matthews, J. R. Jones, “Continuing increase in mesothelioma mortality in Britain,” Lancet 345, 535–539 (1995).
[CrossRef] [PubMed]

Huffman, D. R.

C. F. Bohren, D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley, New York, 1983).

Jones, J. R.

J. Peto, J. T. Hodgson, F. E. Matthews, J. R. Jones, “Continuing increase in mesothelioma mortality in Britain,” Lancet 345, 535–539 (1995).
[CrossRef] [PubMed]

Kaye, P. H.

P. H. Kaye, K. Alexander-Buckley, E. Hirst, S. Saunders “A real-time monitoring system for airborne particle shape and size analysis,” J. Geophys. Res. 101, 19,215–19,221 (1996).
[CrossRef]

E. Hirst, P. H. Kaye, J. Guppy, “Light scattering from non-spherical airborne particles: experimental and theoretical comparisons,” Appl. Opt. 33, 7180–7186 (1994).
[CrossRef] [PubMed]

Lilienfeld, P.

P. Lilienfeld, P. Elterman, P. Baron, “Development of a prototype fibrous aerosol monitor,” Am. Ind. Hyg. Assoc. J. 40, (4), 270–282 (1979).
[CrossRef] [PubMed]

Matthews, F. E.

J. Peto, J. T. Hodgson, F. E. Matthews, J. R. Jones, “Continuing increase in mesothelioma mortality in Britain,” Lancet 345, 535–539 (1995).
[CrossRef] [PubMed]

Mazumder, M. K.

P. A. Baron, M. K. Mazumder, Y. S. Cheng, “Direct reading techniques using optical particle detection,” in Aerosol Measurement, K. Willeke, P. A. Baron, eds. (Reinhold, New York, 1993), pp. 403–408.

Moore, D.

A. P. Rood, E. J. Walker, D. Moore, “Construction of a portable fibre monitor measuring the differential light scattering from aligned fibres,” in Proceedings of the International Symposium: Clean Air at Work, R. H. Brown, M. Curtis, K. J. Saunders, S. Vandrendreissche, eds. (Royal Society of Chemistry, London, 1992), pp. 265–267.

Peto, J.

J. Peto, J. T. Hodgson, F. E. Matthews, J. R. Jones, “Continuing increase in mesothelioma mortality in Britain,” Lancet 345, 535–539 (1995).
[CrossRef] [PubMed]

Rood, A. P.

A. P. Rood, E. J. Walker, D. Moore, “Construction of a portable fibre monitor measuring the differential light scattering from aligned fibres,” in Proceedings of the International Symposium: Clean Air at Work, R. H. Brown, M. Curtis, K. J. Saunders, S. Vandrendreissche, eds. (Royal Society of Chemistry, London, 1992), pp. 265–267.

Saunders, S.

P. H. Kaye, K. Alexander-Buckley, E. Hirst, S. Saunders “A real-time monitoring system for airborne particle shape and size analysis,” J. Geophys. Res. 101, 19,215–19,221 (1996).
[CrossRef]

Taylor, D.

J. Carter, D. Taylor, P. A. Baron, “Fibers method 7400 revision no. 3:5/15/89” in NIOSH Manual of Analytic Methods (U.S. Department of Health and Human Services, Washington, D.C., 1989).

Walker, E. J.

A. P. Rood, E. J. Walker, D. Moore, “Construction of a portable fibre monitor measuring the differential light scattering from aligned fibres,” in Proceedings of the International Symposium: Clean Air at Work, R. H. Brown, M. Curtis, K. J. Saunders, S. Vandrendreissche, eds. (Royal Society of Chemistry, London, 1992), pp. 265–267.

Am. Ind. Hyg. Assoc. J. (1)

P. Lilienfeld, P. Elterman, P. Baron, “Development of a prototype fibrous aerosol monitor,” Am. Ind. Hyg. Assoc. J. 40, (4), 270–282 (1979).
[CrossRef] [PubMed]

Appl. Opt. (1)

J. Geophys. Res. (1)

P. H. Kaye, K. Alexander-Buckley, E. Hirst, S. Saunders “A real-time monitoring system for airborne particle shape and size analysis,” J. Geophys. Res. 101, 19,215–19,221 (1996).
[CrossRef]

Lancet (1)

J. Peto, J. T. Hodgson, F. E. Matthews, J. R. Jones, “Continuing increase in mesothelioma mortality in Britain,” Lancet 345, 535–539 (1995).
[CrossRef] [PubMed]

Other (7)

Testimony of NIOSH on occupational exposure to asbestos, tremolite, anthrophyllite, and actinolite. 29CFR, Parts 1910 and 1926, 9 May 1990.

J. Carter, D. Taylor, P. A. Baron, “Fibers method 7400 revision no. 3:5/15/89” in NIOSH Manual of Analytic Methods (U.S. Department of Health and Human Services, Washington, D.C., 1989).

P. A. Baron, M. K. Mazumder, Y. S. Cheng, “Direct reading techniques using optical particle detection,” in Aerosol Measurement, K. Willeke, P. A. Baron, eds. (Reinhold, New York, 1993), pp. 403–408.

A. P. Rood, E. J. Walker, D. Moore, “Construction of a portable fibre monitor measuring the differential light scattering from aligned fibres,” in Proceedings of the International Symposium: Clean Air at Work, R. H. Brown, M. Curtis, K. J. Saunders, S. Vandrendreissche, eds. (Royal Society of Chemistry, London, 1992), pp. 265–267.

R. O. Duda, P. E. Hart, Pattern Classification and Scene Analysis (Wiley, New York, 1973).

C. F. Bohren, D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley, New York, 1983).

R. C. Brown, J. A. Hoskins, N. F. Johnson, eds. , Mechanisms in Fiber Carcinogenesis, Life Science, Vol. 223 (Plenum, New York, 1991), pp. 1–589.

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Figures (9)

Fig. 1
Fig. 1

Scanning electron micrographs of crocidolite asbestos (top) and chrysotile asbestos (bottom) showing the characteristic needlelike and curved fibers, respectively. Fiber diameters range from submicrometer to a few micrometers.

Fig. 2
Fig. 2

Schematic diagram of the laser scattering test chamber used to collect high-resolution scattering profiles from individual particles carried in a sample airstream.

Fig. 3
Fig. 3

Examples of scattering profiles recorded from individual airborne particles. The upper row illustrates the wide variety of profiles derived from typical background particles; the center row shows profiles from individual crocidolite asbestos fibers; and the lower row shows profiles from individual chrysotile asbestos fibers.

Fig. 4
Fig. 4

Outline diagram of the layout of the custom multielement photodiode detector array used in the new instrument to collect light scattered from individual particles. The array is 11 mm in diameter and is configured on a single silicon substrate. The numbers that appear in each detector element are given to aid comparison with the examples of actual light scattering data given in Fig. 9.

Fig. 5
Fig. 5

Schematic illustration of the basic elements of a RBF neural network.

Fig. 6
Fig. 6

Graphical representation of the simulated performance of the detector configuration (shown in Fig. 4) and the RBF neural network in terms of classifying particles from known aerosols. Ideally, 100% of each test data type should be classified into its correct class.

Fig. 7
Fig. 7

Schematic diagram of the new laser scattering instrument that incorporates the custom photodiode detector array to collect light scattered from individual particles carried in the sample airstream.

Fig. 8
Fig. 8

Schematic diagram showing the acquisition and digitization process for light-scattering signals derived from the custom detector array chip.

Fig. 9
Fig. 9

Typical examples of the output of the detector system of the new instrument. These show the scattered light intensities received by each of the 32 detector channels (1–16 from the outer detector ring A and 17–32 from the middle ring B; refer to Fig. 4) for a single crocidolite asbestos fiber (top), a single chrysotile fiber (middle), and an irregular background particle. Data of this format are fed to the neural network for pattern classification.

Tables (1)

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Table 1 Summary of the Classification of Scattering Profile Data from a Mixed Aerosol Containing Crocidolite, Chrysotile, and Background Particlesa

Equations (3)

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ωix-xi,
classj=i=1nwjiωix-x,j=1,2,,k,
ωix-xi=expx-xi2d2,

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