ct/m3 means counts per cubic meter, the unit a lab uses to express airborne fungal concentration after dividing the raw structures counted on the slide by the volume of air the pump actually drew.
What does ct/m3 mean?
A lab does not report the bare number of spores it saw; it reports a concentration normalized to air volume so two samples taken at different flow rates or durations can be compared. The volume is flow rate times run time, so a pump running at 15 liters per minute for 5 minutes draws 75 liters, or 0.075 cubic meters. If the lab counts 75 structures on that slide, the concentration is 75 divided by 0.075, or 1,000 ct/m3 (ASTM D7391 defines the counting method behind the raw number). The unit is sometimes written spores/m3 for a spore trap or CFU/m3 for a culturable sample; the math is the same, but the populations are not.
Why it matters to a mold inspection
A wrong volume gives a wrong concentration, which is why pump calibration and accurate run-time logging matter as much as the lab work. If the pump was not calibrated, the reported ct/m3 is built on a guessed volume, and the indoor-outdoor ratio derived from it is unreliable. There is no universal pass/fail ct/m3, because outdoor air sets the local baseline and the EPA directs that results be interpreted by a professional against that context (EPA, Mold Remediation in Schools and Commercial Buildings). See air pump calibration and how to read a lab report for the field and interpretation sides.
MoldMind captures flow rate, run time, and volume as structured fields, so the ct/m3 on a report is auditable back to the calibration that produced it.
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Sources
- ASTM D7391: the counting method that produces the raw structure count behind a ct/m3.
- EPA, Mold Remediation in Schools and Commercial Buildings: concentrations require professional interpretation against an outdoor baseline.