The quality of fiber counts using improved slides with relocatable fields

Our plain-English summary of The quality of fiber counts using improved slides with relocatable fields, by T.W. Pang, M. Harper (Journal of Environmental Monitoring, 2008).

The study

• Authors: T.W. Pang, M. Harper
• Journal: Journal of Environmental Monitoring
• Published: 2008;10(1):89-95
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A parameter based on discrepancies between reported fibers and verified fibers of relocatable slides is shown to be effective in monitoring the quality of airborne fiber counts. Analysts report only the fibers in each field examined. The verified fibers were determined by two experienced analysts, and are here considered as a "true" value. Most of the verified fibers were confirmed by the reported fibers, and the disputed fibers or fiber counting errors were all located and accounted for. In this study, reference (REF) slides were manufactured from proficiency analytical test (PAT) filter samples from the American Industrial Hygiene Association containing chrysotile or amosite. The slides were made using coverglasses bearing a grid pattern to allow accurate re-examinations. These coverglasses are an improved version of those used in previous studies. Seventy-four out of 85 amosite results and 51 out of 60 chrysotile results of REF slides were within their PAT proficiency ranges. When all reported fibers were normalized against their respective verified fibers, the average fiber count was over-estimated for amosite by 38.3% and under-estimated for chrysotile by 30.4%. The error from counting short fibers (sizing-extra) was 82.6% of the extra fibers and accounted for the 38% over-estimation of amosite fibers. For chrysotile fibers, sizing-extra errors were 74.0% of the extra fibers, but by far the larger errors were oversight-missing errors, which were 96.7% of the missing fibers and accounted for the 30% under-estimation of the chrysotile fibers. The discrepancies were found to be linearly related to counting errors as had been noted in a previous study, giving further weight to a proposed score, calculated from the discrepancy parameter (SigmaD(+) + |SigmaD(-)|)/VF(total), for evaluating the proficiencies of analysts. If a proficiency score =60 is selected, 48 out of 85 amosite results and 17 out of 60 chrysotile results satisfied this criterion in this study. The number of fiber counting errors in this study was larger than could be expected by PAT proficiency criteria. It may be useful to complement existing proficiency test programs with these REF slides. At the end of each proficiency testing round, detailed reports of discrepancies can be provided to participants so that they can improve on their skills in searching and sizing fibers and minimize their counting errors. In addition, the internal quality control program of each laboratory could include counting REF slides regularly by all analysts with control charts of (SigmaD(+)/VF(total)), (SigmaD(-)/VF(total)), (SigmaD(+) + |SigmaD(-)|)/VF(total) and RF(total)/VF(total) maintained to monitor errors, proficiencies and intercounter variations. Ten percent of relocatable slides of routine samples could also be recounted to monitor intracounter variation.

In plain English

This laboratory study tested new reference slides for checking how accurately analysts count airborne asbestos fibers under a phase contrast microscope. The authors made 47 amosite and 33 chrysotile slides from American Industrial Hygiene Association proficiency test filters. They used coverglasses printed with a grid of numbered circular fields, so each field could be re-examined. Two experienced analysts recorded the 'verified' fibers, which were treated as the true count. Volunteer analysts from proficiency testing programs counted the slides in 2006 and returned 85 amosite and 60 chrysotile counts. Seventy-four of 85 amosite and 51 of 60 chrysotile results fell within the standard proficiency ranges. Compared with the verified fibers, however, analysts over-counted amosite by an average of 38.3%, mostly by counting fibers that were too short. They under-counted chrysotile by 30.4%, mostly by overlooking fibers. Using a proposed discrepancy-based score with 60 as the pass mark, 48 of 85 amosite and 17 of 60 chrysotile results passed. The authors called the number of errors large, noting this is often true in early testing rounds. They concluded that routine use of these slides could probably give greater quality assurance.

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 quality-control study of asbestos fiber counting: relocatable reference slides were sent to volunteer analysts, and their counts were compared field by field with verified fibers
• Who was studied: 47 amosite and 33 chrysotile reference slides, counted in 2006 by volunteer laboratories and microscopists enrolled in the AIHA IHLAP asbestos PAT or the Asbestos Analytics Registry proficiency testing programs. They reported 85 amosite and 60 chrysotile fiber counts.
• Exposure: Slides made from AIHA proficiency analytical test filter samples containing chrysotile or amosite, counted by phase contrast microscopy using NIOSH 7400 'A' counting rules
• Main results:
  • Within the standard PAT proficiency ranges: 74 of 85 amosite results and 51 of 60 chrysotile results
  • Compared with verified fibers, the average count was over-estimated by 38.3% for amosite and under-estimated by 30.4% for chrysotile. Ratios of reported to verified fibers ranged from 0.714 to 3.785 for amosite and from 0.128 to 1.290 for chrysotile.
  • Amosite: counting short fibers (sizing-extra errors) made up 82.6% of the extra fibers and accounted for the over-estimation
  • Chrysotile: oversight-missing errors were 96.7% of the missing fibers and accounted for the under-estimation
  • With a proficiency score of 60 as the criterion, 48 of 85 amosite results and 17 of 60 chrysotile results passed
  • The authors described the overall number of errors as large, with a number of laboratories or microscopists not reaching the suggested acceptable standard
  • Placing the Walton–Beckett graticule within the circular viewing field did not seem to change total counting errors, compared with a previous study
• The authors' conclusion: The authors concluded that greater quality assurance in fiber counting would be desirable and could probably be achieved by more routine use of these reference slides
• Limitations the authors state:
  • This was the first exposure to relocatable slides for most AIHA participants, and a learning curve was anticipated
  • Large numbers of errors are often seen in the initial rounds of proficiency testing studies
  • The 'A' counting rules have no upper limit on fiber width. This was not a significant issue with the asbestos-only test samples but could be an issue with real-world samples and different counting rules.

Topics

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

Medical terms in this study, explained in our Lexicon: Fiber Counting, Industrial Hygiene, Chrysotile, Amosite.

Related studies

• Continued participation in an asbestos fiber-counting proficiency test with relocatable grid slides — M. Harper, J.E. Slaven, et al. (2009)
• Evaluation of the dark-medium objective lens in counting asbestos fibers by phase-contrast microscopy — E.G. Lee, J.H. Nelson, et al. (2015)
• Evaluation of asbestos-containing products and released fibers in home appliances — S.H. Hwang, W.M. Park (2016)
• Real-time measurement of fibers using an HY-differential mobility analyzer with an optical particle counter (KOFAM) — S. Choi, K. Jang, et al. (2017)
• Performance of membrane filters used for TEM analysis of asbestos — J.S. Webber, A.G. Czuhanich, et al. (2007)
• Comparison of direct and indirect methods of measuring airborne chrysotile fibre concentration — C. Eypert-Blaison, S. Veissiere, et al. (2010)

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