The effect of a proposed change to fiber-counting rules in ASTM International Standard D7200-06

Our plain-English summary of The effect of a proposed change to fiber-counting rules in ASTM International Standard D7200-06, by M. Harper, E.G. Lee, B. Harvey, et al (Journal of Occupational and Environmental Hygiene, 2007).

The study

• Authors: M. Harper, E.G. Lee, B. Harvey, M. Beard
• Journal: Journal of Occupational and Environmental Hygiene
• Published: 2007;4(5):D42-5
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Summary of the article

The authors examined how a proposed change to the fiber-classification rules in ASTM International Standard D7200-06 would affect the counting of amphibole cleavage fragments as potentially asbestiform fibers. Under the current standard, particles meeting the NIOSH 7400 "A" fiber definition (>5 μm long, aspect ratio ≥3:1) are assigned to Class 1 if curved or bundle-like, to Class 2 if >10 μm long or <1 μm wide, and otherwise to Class 3. The proposed alternative defines Class 2 as >10 μm long and <1 μm wide. The authors analyzed 77 air samples from a taconite mine ore-processing mill. Using the current criteria, 28% of fibers were Class 1 and 18.6% were Class 2. They also examined about 300 particles each from crushed nonasbestiform actinolite and tremolite, both identified by X-ray diffraction. Almost no particles were Class 1. Under the current and proposed Class 2 definitions, fibers in Class 2 were 25.1% and 0.6% for actinolite and 46.8% and 1.6% for tremolite. In the mine samples, Class 2 fell to about 0.8% under the proposed definition. A 3 μm width cut-off reduced Class 2 less in the mine samples, from 18.6% to 15.2%. The authors concluded that the current rules classify many cleavage fragments as potentially asbestiform, while the proposed change would place them almost entirely in Class 3. They noted that whether the change would also misclassify true asbestiform fibers had not been addressed. The data were described as provisional and not peer reviewed.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This report, which the authors said contained provisional data that had not been peer reviewed, tested how the fiber-counting rules in ASTM International Standard D7200-06 sort particles seen under a phase contrast microscope. The rules place particles into potentially asbestiform fibers (Classes 1 and 2) or other particles, including cleavage fragments (Class 3). The authors used materials expected to contain mostly cleavage fragments rather than asbestiform fibers: crushed coarsely crystalline actinolite and tremolite, with about 300 particles examined for each, and 77 air samples from a taconite mine ore-processing mill. Under the current Class 2 definition, 25.1% of actinolite fibers and 46.8% of tremolite fibers fell in Class 2. Under a proposed definition, these fell to 0.6% and 1.6%. In the mill samples, Class 2 fell from 18.6% to about 0.8%. A 3 μm width limit also reduced Class 2 counts, but less so in the mill samples. The authors concluded that the current rules designate many cleavage fragments as potentially asbestiform. They noted they had not addressed how far the proposed change might also classify actual asbestiform fibers as Class 3.

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 evaluation of fiber-classification counting rules (not a health study); reported as provisional data that had not been peer reviewed
• Who was studied: Crushed non-asbestiform actinolite (from a mineral dealer, said to be from near Wrightwood, San Bernardino County, Calif.) and a previously crushed tremolite stockpile from NIEHS of unknown provenance, with about 300 particles examined from each; plus 77 air samples from a taconite mine ore-processing mill
• Exposure: Particles from coarsely crystalline (non-asbestiform) actinolite and tremolite, and taconite mill air containing tremolite-actinolite and cummingtonite-grunerite series amphiboles. Particles were classified under the current D7200-06 Class 2 definition (longer than 10 μm or narrower than 1 μm) and a proposed definition (longer than 10 μm and narrower than 1 μm).
• Main results:
  • In the taconite mill air samples, there was an average of 83.8 fibers per 85.6 fields. Under the current rules, 28% of fibers met Class 1 and a further 18.6% met Class 2.
  • Crushed actinolite: 58.3% of particles met the NIOSH 7400 fiber definition. Of these fibers, 25.1% were in current Class 2 and 0.6% in the proposed Class 2.
  • Crushed tremolite: 62.7% of particles met the NIOSH 7400 fiber definition. Of these fibers, 46.8% were in current Class 2 and 1.6% in the proposed Class 2.
  • Almost none of the crushed mineral particles had Class 1 characteristics.
  • In the mill samples, the Class 1 proportion was unchanged under the proposed definition, while Class 2 fell to about 0.8%.
  • Applying a 3 μm width cut-off had these effects. Actinolite: fibers went from 58% to 48% of total particles and Class 2 from 25% to 14%. Tremolite: fibers went from 63% to 43% and Class 2 from 47% to 29%. Mill samples: Class 2 went from 18.6% of 83.8 fibers to 15.2% of 80.4 fibers.
• The authors' conclusion: The authors concluded that the current classification rules designate many cleavage fragments as Class 2 (potentially asbestiform), whereas the proposed change would place them almost exclusively in Class 3 (nonasbestiform).
• Limitations the authors state:
  • The authors had not addressed how far the proposed change might classify actual asbestiform fibers as Class 3, for example thick bundles without curvature or splayed ends.
  • A small amount of asbestiform fiber contamination in the mineral specimens could not be ruled out, though the authors judged it unlikely to exceed a few percent.
  • Measurements of the crushed amphiboles were made by eye and rounded to the nearest micrometer, which required assumptions about rounding.
  • The data were provisional and had not been peer reviewed.

Topics

Medical terms in this study, explained in our Lexicon: Amphibole Group, Cleavage Fragment, Asbestiform, NIOSH Method 7400, Aspect Ratio (Length-to-diameter ratio), Taconite, Non-Asbestiform, Actinolite.

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