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Why Mold Abatement Requires Negative Air Pressure & HEPA Filtration

The Institute of Medicine has linked inhaled mold spores to coughing, wheezing, and asthma. How can dangerous mold be safely eliminated?

Molds are members of the fungi kingdom. Estimates of the number of species of molds range from 50,000 to 300,000, with about 200 having been defined as pathogens that can cause infections in humans.

Found everywhere in nature, molds love dampness and reproduce by launching microscopic spores into the air, which means that when they find a moist place to reproduce inside a building, bad news ensues.

Flooding, water leaks, and poorly designed HVAC systems are all breeding grounds for molds. They can get pretty creative about where to set up shop, too. One hospital mold problem was traced to a pinhole leak in the supply line to a water cooler. In an older section of Cape Coral Hospital in Florida, wallpaper near the windows in patient rooms was trapping condensation and causing discoloration from mold, so the hospital replaced the drywall and painted it, fortunately before any illnesses were traced to it.

The CDC asked the Institute of Medicine (IOM) to find out how detrimental effects of inhaling mold. In 2004, IOM found links to upper respiratory tract symptoms such as coughing and wheezing in otherwise healthy people and a life-threatening condition called hypersensitivity pneumonitis in susceptible individuals.

Though the danger of mold spores to hospital patients and staff has been known for more than 15 years, incidents such as these continue to occur:

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How should a healthcare facility respond to a mold problem?

If you discover mold in your facility, these are some general steps to take:

  • Determine the cause and scope of the problem.
  • Eliminate the source of moisture.
  • Perform an infection control risk assessment.
  • Relocate patients if necessary.
  • Contain the affected area.
  • Control airflow.
  • Remediate.
  • Clean up, test, and return to normal operation.

In this post, we're primarily concerned with containment, and airflow control, so let's take a look at those.

Contain the area

Whether you're facing a large or small mold abatement project, the first thing to do is to seal off the area affected by mold, just as you would a dust-producing construction site. You can use containment methods ranging from plastic to drywall to temporary wall barriers.

The HVAC system must be isolated from the rest of the building, and taping may be necessary to seal room leaks around windows or other openings.

To allow technicians to clean equipment and change protective gear when going in and out of the work area, an anteroom should be set up to serve as an entryway. One can be constructed from conventional materials, or a modular anteroom such as HEPACART®'s AnteRoom may be deployed. One advantage of a reusable unit, besides quick setup and a surface that cleans easily, is that it comes with adapters to connect to negative air machines.

Once the work area is contained, you're ready for the next step.

Control airflow with a negative air machine

To make sure spore-contaminated air stays doesn't escape, the work area must have a lower pressure than the area outside it. This negative air pressure is created by installing a negative air machine with HEPA filtration.


Since HEPA filters are designed to remove at least 99.7% of particles 0.3 micrometers or larger, and mold spores range in size from about 4 to 20 micrometers, the negative air machine will remove mold spores before exhausting it from the room.

A good negative air machine will have a primary filter treated with an anti-microbial additive in the airstream through which the air flows before entering the HEPA filter. Further, it should be possible to tailor the filters to the specific job. For example, HEPACART®'s OMNIAIRE negative air machines can be customized with various filters depending on whether dust, spores, or other pathogens are the main target.

How powerful does your negative air machine have to be? To achieve the commonly used target of 12 ACH (air changes per hour), divide cubic feet per minute (CFM) by cubic feet of the area, and multiply by 60.

According to that formula, a negative air machine pulling 500 CFM from a 2,500 cubic foot area would completely change the air once every five minutes, or 12 times an hour.

If pathogens besides mold are suspected, such as viruses that are small enough to pass through a HEPA filter, an air scrubber using UV light can be deployed. One such device is HEPACART®'s Airborne Pathogen Disinfection Module, which uses far-UV light to physically destroy pathogen cells, adding a secondary level of protection.

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Perform remediation, clean up, and return to normal operation

Once the containment system is in place around the contaminated space, work can begin, cleaning what's cleanable and removing what's not, like furnishings, furniture, carpet, and possibly even walls.

Often this job is left to mold abatement experts who have the proper methods, equipment, and materials to clean and disinfect everything in the area. They may also need to package and remove contaminated medical supplies.

Cleanup includes both HEPA vacuuming and hand-cleaning with disinfectant. As a test of effectiveness, resistance performance testing using biological indicators may be used.

A spore inoculated biological indicator is like a reverse canary-in-the-coal-mine. By placing known hard-to-kill spores in a cleanup area, you can determine the effectiveness of the sterilization job because if it kills them, you can be sure that less robust spores have been eliminated.

Many of the same containment methods and tools used in hospital construction to control airborne dust and pathogens also can be used for mold abatement projects. We hope this post has raised your awareness of the dangers of free-roaming mold spores, and the remedies that may already be in your possession.

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