> > I seek authoritative answers.

Authoritative answers would require an on site visit.

With that caveat, my experience in looking at aging ventilation ductwork suggests to me (in a non-authoritative way) that black linty stuff in systems with 24/7 air movement is environmental dust that accumulates in areas of the duct where air speed drops. If I wanted to be somewhat more authoritative, I would collect some of the dust, mix it with water and see the resulting pH is. This would help me determine if it requires more extensive chemical investigation is appropriate.

Good luck!

- Ralph

Ralph Stuart, CIH, CCHO
Environmental Safety Manager
Keene State College
603 358-2859

ralph.stuart**At_Symbol_Here**keene.edu

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