Negative air machine

A negative air machine is a powerful filtered fan. It draws air from the sealed work area, runs it through a HEPA filter, and exhausts it clean. Because more air leaves than enters, small gaps pull air in instead of letting it out.

EPA's mold guide says the containment area must be maintained under negative pressure relative to surrounding areas, so contaminated air does not flow into adjacent areas. It names a HEPA-filtered fan unit as one way to do it. OSHA's asbestos standard uses the same idea for its negative pressure enclosures.

You can tell it is working. Plastic sheeting bows slightly inward. A smoke test or gauge can confirm it.

Ask the crew to keep the unit running through the job, not only during active work. After the job, the unit often stays on until the area passes clearance testing. The machine only works if the containment is tight, so the two go together.