ACGIH is best known to inspectors for the thing it refuses to do: publish a number you can fail an air sample against. That refusal is the point of the reference, and understanding why keeps you from writing a limit into a report that no standard actually set.
What is ACGIH Bioaerosols: Assessment and Control?
Bioaerosols: Assessment and Control is published by the American Conference of Governmental Industrial Hygienists (ACGIH). It is the reference for assessing biological aerosols — fungi, bacteria, and their byproducts — in indoor environments, covering sampling methodology, species significance, and control strategy (ACGIH, Bioaerosols: Assessment and Control). For mold work it sits alongside the AIHA Green Book and IICRC S520 as one of the three references a thorough assessment leans on.
ACGIH is the organization that publishes Threshold Limit Values for chemical exposures, which makes its position on mold notable: it does not set one.
Does ACGIH set an exposure limit for mold?
No. ACGIH does not publish a numeric occupational exposure limit (OEL) for airborne mold or fungal spores, and Bioaerosols: Assessment and Control explains why — the dose-response relationship for mold exposure is too variable across individuals and organisms to support a single defensible threshold. The EPA states the same conclusion for the public: there are no EPA or federal limits for mold or mold spores in the air (EPA, Mold and Health).
This is the single most cited-and-misused fact in mold assessment. Because no OEL exists, a report that says a sample "exceeded the ACGIH limit" is asserting something ACGIH explicitly declined to publish. The honest version describes the relative finding and the indicator organisms, and never invokes a number the reference disclaims.
How does ACGIH say to assess fungal bioaerosols?
ACGIH frames assessment as relative and multi-factor rather than threshold-based. Without an OEL to compare against, the assessment rests on the indoor-versus-outdoor comparison, the diversity and identity of the species present, the presence of indicator organisms, and the building conditions — visible growth, moisture, and occupant complaints. A finding is the convergence of these, not a single count crossing a line.
The reference gives particular attention to indicator species. Organisms like Stachybotrys, Chaetomium, and Fusarium warrant specific commentary because they signal sustained water damage rather than ordinary background ecology. Aspergillus and Penicillium matter when they are amplified indoors relative to outdoors. Cladosporium, common outdoors, usually reflects outdoor infiltration unless it dominates indoors. That species-by-species judgment, not a number, is the ACGIH method.
How do you cite ACGIH in a report?
Attribute the interpretive framework to the reference by title — "assessed per ACGIH's Bioaerosols: Assessment and Control" — and pair it with the actual indicator-species commentary and indoor-outdoor comparison you performed. ACGIH publications are purchased documents, so cite at the level the title supports and never fabricate a chapter clause or a limit. The defensible report uses ACGIH to justify why there is no pass/fail number and to anchor the indicator-species notes.
MoldMind's assessment logic mirrors this relative framework: it compares indoor results to the outdoor control rather than to a fixed threshold, and it surfaces indicator-species commentary where organisms like Stachybotrys or Chaetomium appear (CDC, Basic Facts about Mold and Dampness, reinforces the moisture-first reading). See the sample report and the when-each-standard-applies guide.
Sources
- ACGIH, Bioaerosols: Assessment and Control — relative, multi-factor fungal assessment; no mold OEL.
- EPA, Mold and Health — no federal numeric limit for airborne mold.
- CDC, Basic Facts about Mold and Dampness — assessment keyed to dampness and visible growth.