Study of the count-to-mass conversion factor for asbestos fibres in samples collected at the emissions of three industrial plants

Our plain-English summary of Study of the count-to-mass conversion factor for asbestos fibres in samples collected at the emissions of three industrial plants, by S. Puledda, A. Marconi (The Annals of Occupational Hygiene, 1991).

The study

• Authors: S. Puledda, A. Marconi
• Journal: The Annals of Occupational Hygiene
• Published: 1991;35(5):517-24
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Count-to-mass conversion factors for asbestos fibres in the stack emissions of three industrial plants were calculated. Dust samples deriving from different working processes were collected downstream from the fabric-based filtration systems. Gravimetric measurements were carried out utilizing an X-ray diffraction procedure based on the use of a silver filter that permits the correction for X-ray absorption by the sample. The number of fibres covered by regulations ('Regulated fibres') (F) was counted by phase-contrast optical microscopy (PCOM) on a section of the same filter as had been used for gravimetric measurements. The values of the conversion factors vary widely, ranging from 0.4 x 10(3) to 4.9 x 10(3) fibers per microgram (F microgram -1) according to the working process involved. They are always less than 20 x 10(3) F microgram -1, the value specified in the EEC Directive 217/87 concerning the prevention of asbestos pollution in the environment.

In plain English

This study measured asbestos in dust leaving the stacks of three industrial plants: an asbestos-cement sheet factory using chrysotile, an asbestos-cement pipe factory using chrysotile and crocidolite, and a chrysotile mining and milling plant. Samples were collected after the plants' fabric filtration systems, at least three for each working process. On each filter, the authors measured asbestos mass by X-ray diffraction and counted 'regulated fibres' by phase-contrast optical microscopy. They then calculated a count-to-mass conversion factor, meaning the number of fibres per microgram of asbestos. These factors ranged from 0.4 x 10^3 to 4.9 x 10^3 fibres per microgram. All were lower than the 20 x 10^3 value in EEC Directive 217/87. Asbestos mass concentrations in the two asbestos-cement plants were always below 0.1 mg per cubic metre, while mining activities often exceeded that limit. As the particulate mass rose, the conversion factor tended to fall (correlation coefficient minus 0.65). The authors concluded that the Directive's conversion factor seemed not sufficiently reliable and that further studies were needed. They noted a limited data set and sources of error such as uneven dust deposits on filters.

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: Measurement study of stack emission samples comparing asbestos mass (X-ray diffraction, silver filter method) with regulated-fibre counts (phase-contrast optical microscopy) on the same filters
• Who was studied: Stack emissions of three industrial plants: an asbestos-cement sheet factory, an asbestos-cement pipe factory, and a chrysotile mining and milling plant. At least three samples were taken for each working process. Location and dates of sampling are not stated.
• Exposure: Chrysotile and crocidolite in dust collected downstream from fabric-based air filtration systems. Working processes included packing, silo storing, oven drying, splitting, bag opening, cutting, smoothing and turning.
• Main results:
  • Across all samples from the three plants, count-to-mass conversion factors ranged from 0.4 x 10^3 to 4.9 x 10^3 fibres per microgram.
  • All conversion factors were lower than the value of 20 x 10^3 fibres per microgram specified in the EEC Directive.
  • Asbestos mass concentrations in the two asbestos-cement plants were always below 0.1 mg per cubic metre. In mining activities they often exceeded this limit.
  • Asbestos mass concentrations were generally highest in mining activities and lowest in asbestos-cement sheet production.
  • Variability of conversion factors was much lower when samples were grouped by working process. The greatest variability within a process, expressed as coefficient of variation, was around 50%, for bag opening in the asbestos-cement sheet plant.
  • There was an inverse relationship between particulate mass and the count-to-mass conversion factor, with a correlation coefficient of minus 0.65.
• The authors' conclusion: The authors concluded that the conversion factor proposed by EEC Directive 217/87 seemed not sufficiently reliable. They called for further studies, at least for the most polluting industrial sectors, using methods representative of stack emissions. They attributed the poor reproducibility and low conversion factors largely to the counting criteria of the EEC membrane filter method.
• Limitations the authors state:
  • The results are based on a limited set of data.
  • The authors stated that the sources of error they described limit how far the data can be regarded as representative.
  • Dust was unevenly distributed on some filters. Only samples with acceptable uniformity were analysed, and some samples were discarded because particle density was too high for counting.
  • To avoid excluding too many samples, filters with fibre densities outside the range recommended by the EEC method were included. Each sample was counted three times by the same operator to reduce error.
  • The sampling system may have caused losses of asbestos particles along the probe walls.

Topics

Medical terms in this study, explained in our Lexicon: X-Ray Diffraction (XRD).

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