The record
NIOSH's 2011 state-of-the-science review on asbestos fibers and other elongated mineral particles (Publication No. 2011-159) documents that the analytical method routinely used for occupational asbestos exposure (phase contrast microscopy) cannot differentiate nonasbestiform 'cleavage fragment' analogs from asbestos fibers by physical appearance, and that further research is needed on the health risks of non-asbestiform EMPs.
Claim scope
That the fiber-vs-cleavage-fragment identification problem is recognized in the federal occupational-health literature, including the limits of PCM for distinguishing the two.
What this source does not establish
NIOSH does not endorse the defense claim that cleavage fragments are harmless — the document calls for more research on EMP toxicity — nor does it resolve the controversy in either direction. The context is occupational airborne exposure, not cosmetic talc testing specifically.
Limitations
Use as the neutral federal anchor for the mineralogical-war section; attribute positions on both sides (Rohl/Langer caveat, defense experts) separately.
Source
Gov Report — NIOSH Publication No. 2011-159, 'Asbestos Fibers and Other Elongated Mineral Particles: State of the Science and Roadmap for Research' (DHHS/NIOSH, April 2011)