Negative air is the use of a HEPA-filtered air machine (an air scrubber or negative-air machine) to keep a mold containment at a lower pressure than the surrounding space, so air leaks into the containment rather than out and the machine's exhaust is filtered clean.
What is negative air?
A negative-air machine pulls air out of the sealed containment through a HEPA filter and exhausts it, usually outside the building. Removing air faster than it leaks in drops the containment to negative pressure relative to the clean side, so every gap pulls clean air inward instead of pushing contaminated air out. This does two jobs at once: it captures airborne spores on the HEPA filter, and it guarantees the direction of any leakage. The EPA pairs containment with this kind of pressure control and HEPA filtration for larger remediation projects (EPA, Mold Remediation in Schools and Commercial Buildings).
Why it matters to a mold inspection
Containment without negative pressure can still leak contamination outward through the inevitable gaps; the negative pressure is what makes containment reliable. A clearance inspector confirms negative air was running and that the exhaust was HEPA-filtered, because a containment under neutral or positive pressure has been spreading spores the whole time. OSHA treats this filtered-pressure control as standard engineering control for mold work (OSHA, Mold). See containment and negative air and HEPA and PPE in mold work.
MoldMind's protocol output records whether negative air and HEPA filtration are specified, so the engineering control is a checkable line in the scope rather than an assumption.
Sources
- EPA, Mold Remediation in Schools and Commercial Buildings: pressure control with HEPA filtration accompanies containment on larger jobs.
- OSHA, Mold: filtered negative-pressure control is a standard engineering control for mold removal.