Variation in fibre and dust counts in an asbestos mine and mill

Our plain-English summary of Variation in fibre and dust counts in an asbestos mine and mill, by R.C. Parsons, D.G. Bryant, H.W. Edstrom (The Annals of Occupational Hygiene, 1986).

The study

• Authors: R.C. Parsons, D.G. Bryant, H.W. Edstrom
• Journal: The Annals of Occupational Hygiene
• Published: 1986;30(1):63-75
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

In plain English

This study measured airborne fibres and dust at a chrysotile asbestos mine and mill in Baie Verte, Newfoundland, to judge whether old records could estimate exposure. In 1981 the authors ran 12 paired midget impinger and membrane filter samplers side by side. In August and September 1981 they took 189 filter samples covering three mill zones, three shifts and every day of the week. They also reviewed older records from two companies and government inspectors. Examined by the same microscopy, both sampler types gave equivalent fibre counts. In the screening zone, 33 of 63 samples exceeded 5 fibres per ml; Friday-to-Monday levels were significantly above mid-week levels. In refining and bagging zones, 3 of 126 samples exceeded 2 fibres per ml. The agencies sampled with equal precision, though inspectors' averages were higher. Conversion ratios varied by zone and year, and the authors concluded that no single ratio was reasonable. They recommended calculating exposure from zone averages by day of week or by mid-week and weekend periods, though day-of-week effects might have to be ignored historically. The fibres counted were not identified as asbestos.

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 study (1981 static sampling) combined with analysis of historical air monitoring records
• Who was studied: Air in the chrysotile asbestos mine and mill at Baie Verte, Newfoundland, Canada. In 1981 there were 12 paired midget impinger and membrane filter samples, plus 189 membrane filter samples (August and September 1981) from the screening, refining and bagging zones of the mill. Historical records came from the operating company, the parent company and government inspectors (1969-1974; 7170 compliance measurements in total for 1965-1980).
• Exposure: Airborne chrysotile asbestos dust and fibres. Fibres longer than 5 micrometres ("respirable fibres") were counted by phase contrast microscopy, and dust particles were measured in millions of particles per cubic foot. Ore in the screening zone was about 4% asbestos, refining feed 60-90%, and bagged product over 99%.
• Main results:
  • When the impinger samples were filtered onto membranes and assessed in the same manner as the membrane filter samples, the side-by-side samplers gave equivalent estimates of airborne fibre levels.
  • The most common fibre lengths were the 3.0-4.2 and 4.3-6.0 micrometre classes for both samplers in all three mill zones.
  • Screening zone: of 63 samples, 33 were over 5 fibres per ml, 19 were 2-5 fibres per ml, and 6 were under 0.5 fibres per ml.
  • Refining and bagging zones: only 3 of 126 samples exceeded 2 fibres per ml, and 57 were under 0.5 fibres per ml.
  • In the screening zone, Friday-to-Monday fibre levels were significantly higher than mid-week (Tuesday to Thursday) levels. In the refining and bagging zones there were no practical differences between days.
  • For the 1981 paired samples (10 of 12 pairs usable), the ratio of membrane filter fibres to impinger particles ranged from 1.5 to 48.5, with a mean of 13.4 plus or minus 26.7 (standard deviation).
  • Conversion ratios estimated from the 1969-1974 records rose from 1969 to 1974 in all zones and from the pit to the bagging end of the operation. This prevented calculating zone, yearly or overall average ratios.
  • The three monitoring agencies had similar variances, meaning the same precision. The two companies' average particle counts were similar to each other and significantly lower than the government inspectorate's average (matched locations: 1.4, 1.8 and 3.1 mppcf). The authors attributed this to inspectors sampling only on Fridays and counting at higher magnification.
• The authors' conclusion: The authors concluded that worker exposure should be calculated from zone averages by day of the week or by mid-week and weekend periods. They noted that day-of-week effects may have to be ignored in historical analyses. They also found that variation between shifts did not warrant stratification, that all agencies' data had the same precision, and that selecting a general particle-to-fibre conversion ratio was not reasonable.
• Limitations the authors state:
  • The fibres counted were unidentified, so the counts were maximum asbestos fibre densities. The authors could not determine the proportion of asbestos fibres in a sample.
  • The historical conversion ratios rested on an untested assumption that old wet cell counts of commercial fibres matched later phase contrast counts.
  • The methods did not account for variation in fibre deposition on the filter.
  • The data do not address the relation between fibre size and disease.
  • The study did not identify the cause of the high weekend fibre levels in the screening zone.
  • Day-of-week effects may have to be ignored in historical analyses because each day of the week will not have been sampled within a short period.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Advocate Mines, Burlington Peninsula, Newfoundland

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Chrysotile.

Related studies

• Relationships between simultaneous airborne dust samples taken with five types of instruments at South African asbestos mines and mills — R.S. Du Toit, L.W. Isserow, et al. (1983)
• Size and shape of airborne asbestos fibres in mines and mills — C.Y. Hwang (1983)
• A comparison of parallel dust and fibre measurements of airborne chrysotile asbestos in a large mine and processing factories in the Russian Federation — E. Feletto, S.J. Schonfeld, et al. (2017)
• Simultaneous airborne dust samples with konimeter, thermal precipitator and dosimeter in asbestos mines — R.S. du Toit, T.C. Gilfillan (1977)
• Late progression of radiographic changes in Canari chrysotile mine and mill exworkers — J.R. Viallat, C. Boutin, et al. (1983)
• Rheumatic complaints and pulmonary response to chrysotile dust inhalation in the mines and mills of Quebec — F.M. White, J. Swift, et al. (1974)

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