Chatfield EMPs

"Chatfield EMPs" refers to the counting and identification rules for elongate mineral particles proposed by mineralogist Eric J. Chatfield, used when analyzing dust, tissue, or product samples for asbestos by transmission electron microscopy (TEM). The protocol specifies size thresholds (typically longer than 5 micrometers with an aspect ratio of at least 3:1) and requires fibers be confirmed by morphology, electron diffraction, and elemental analysis. It is one of several competing schemes used to decide which particles "count" as asbestos in a given sample.

Origin

Named for Eric J. Chatfield, a Canadian analytical mineralogist whose laboratory work from the 1970s onward helped establish modern TEM methods for asbestos in water, air, and bulk materials. His counting rules grew out of EPA-sponsored drinking water studies and have been refined in published protocols and expert reports over several decades.

Significance in Asbestos Context

Which counting rules an analyst uses can change whether a product, a workplace air sample, or a lung tissue digest is reported as "containing asbestos" or "below detection." In litigation, defense and plaintiff experts frequently disagree about whether short fibers, cleavage fragments, or non-regulated EMPs should be included, and the Chatfield rules, which generally require strict mineralogical confirmation but also recognize thinner and shorter fibers that some other methods exclude, often produce different fiber counts than NIOSH or OSHA-style protocols. For a patient, this matters because the same talc, joint compound, or insulation sample can be called "asbestos-containing" under one counting scheme and "asbestos-free" under another, directly affecting product-identification evidence in a case.

Example Sentence

The plaintiff's expert re-analyzed the cosmetic talc using Chatfield EMP counting rules and identified tremolite and anthophyllite fibers that the manufacturer's lab had not reported.

Related Terms

Transmission Electron Microscopy (TEM), Elongate Mineral Particle (EMP), ISO 10312, NIOSH 7402, Cleavage Fragment, Aspect Ratio

Notes

• If your case involves talc, vermiculite, or other contested products, ask your legal team which counting protocol each side's expert used (Chatfield, ISO 10312, NIOSH 7402, or Berman & Crump) and whether re-analysis under a different protocol is warranted.
• Preserve any product samples, original packaging, or workplace dust samples; these may later be tested under stricter EMP rules that detect fibers earlier methods missed.
• Request that any TEM analysis report explicitly state the counting rules, size thresholds, and aspect-ratio cutoffs used, along with SAED and EDS confirmation for each fiber counted.
• Be aware that a "non-detect" result under one protocol does not necessarily mean a product was asbestos-free; this is a common point of expert disagreement in product-identification disputes.