When inspectors say "interpret per AIHA," they usually mean the Green Book — the industrial-hygiene reference that explains how to sample for mold and, harder, how to read the numbers the lab sends back.
What is the AIHA Green Book?
The AIHA Green Book is Recognition, Evaluation, and Control of Indoor Mold, published by the American Industrial Hygiene Association (AIHA). It is the profession's working reference for mold sampling strategy and result interpretation — when to sample, how to collect a representative sample, and how to make sense of an air or surface result once it comes back (AIHA, Recognition, Evaluation, and Control of Indoor Mold). AIHA also publishes a companion Field Guide for the Determination of Biological Contamination in Environmental Samples for the hands-on collection side.
It is a guidance document, not a regulation. It does not set a legal limit, and it is explicit that mold assessment is comparative rather than threshold-based. That orientation is the whole reason inspectors cite it.
What does the Green Book say about sampling strategy?
The Green Book's central contribution is sampling strategy — the decision of whether to sample at all, and if so, how to do it so the result means something. The recurring theme is that sampling is not automatic: visible growth and a moisture source often answer the question without a single cassette. When you do sample, the guidance covers cassette selection, flow rate, sample volume, pump calibration, and the requirement for a same-day outdoor control as the baseline for comparison.
The outdoor control is the part inspectors skip at their peril. An indoor air result has no meaning in isolation, because outdoor fungal ecology varies by region, season, and the day's weather. Without a same-day outdoor sample from the same equipment, you have a number with nothing to compare it to. The Green Book frames the indoor-to-outdoor comparison as the core interpretive move.
How does AIHA say to interpret an air sample result?
AIHA interpretation is relative, not absolute. There is no Green Book "pass" number; the analysis is whether the indoor sample is consistent with a normal outdoor fungal ecology or shows amplification of specific organisms. Two signals carry the most weight: the indoor-to-outdoor relationship for indicator genera like Aspergillus and Penicillium, and the presence indoors of organisms not expected in a clean indoor environment, such as Stachybotrys.
In practice, an indoor sample whose dominant species and counts track the outdoor control reads as no indoor amplification. An indoor sample where Aspergillus/Penicillium runs well above the outdoor baseline reads as a likely indoor source. Stachybotrys indoors at any meaningful count gets flagged regardless of ratio, because it points to sustained wet conditions. None of this is a number you compare to a published limit — the EPA and CDC both state there is no health-based numeric standard for indoor mold (EPA, A Brief Guide to Mold, Moisture and Your Home; CDC, Basic Facts about Mold and Dampness).
How do you cite the Green Book accurately?
Cite it by title and attribute the interpretive logic to it, not to a specific clause you have not read. The Green Book is a purchased AIHA publication, so the defensible citation is "interpreted per AIHA's Recognition, Evaluation, and Control of Indoor Mold," paired with the actual comparison you ran — indoor versus outdoor, indicator-species flags. Do not assert a Green Book threshold number; the document's position is that no such universal number exists.
MoldMind builds the indoor-versus-outdoor comparison from the lab's structured results and flags indicator species automatically, which keeps the interpretation aligned with the AIHA framework instead of leaving a raw count to imply a verdict. See how the lab analysis renders in the sample report, and the when-each-standard-applies guide for how AIHA fits alongside ACGIH and IICRC.
Sources
- AIHA, Recognition, Evaluation, and Control of Indoor Mold — sampling strategy and comparative interpretation.
- EPA, A Brief Guide to Mold, Moisture and Your Home — no health-based numeric mold standard.
- CDC, Basic Facts about Mold and Dampness — assessment keyed to moisture and visible growth, not a count.