Got mold?

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Reopening buildings amid the pandemic

In September, the Centers for Disease Control and Prevention released updated guidance on reopening buildings after a prolonged shutdown. Included are steps to minimize mold risk during and after that dormancy. Those steps are:

  • Keep indoor humidity as low as possible, not exceeding 50%, as measured by a humidity meter. Building managers also can use a digital hygrometer, “ideally more than once daily,” to minimize the need to access the building.
  • Check buildings for excess moisture or mold. Consider inspections with trained industrial hygienists who can recognize mold by sight or odor “without the need for sampling or laboratory analysis.” Building personnel also can use the aforementioned NIOSH assessment resource.
  • If mold or dampness is detected, address the source of water entry first.
  • If the building’s HVAC system hasn’t been active during a shutdown, it should be operated for 48 to 72 hours (also known as a “flush out” period) before workers return. Open outdoor dampers to the maximum setting that doesn’t affect desired indoor air temperatures.
  • Check for odors after the “flush out” period. Assess HVAC filters and replace as necessary.

When the building is reopened and occupied again, perform routine checks of the HVAC system. Those sys-tem checks can be gradually reduced “depending on the operational and maintenance specifications for the HVAC system.”

Cleanup completion checklist

OSHA outlines four general steps to determine when remediation/cleanup should be considered complete:

  1. You have identified and corrected the source(s) of the water/moisture problem.
  2. Visible mold, mold-damaged materials or odors are gone.
  3. Sampling should “show that the level and types of mold and mold spores inside the building are similar to those found outside.”
  4. You have revisited the area where the mold was to check for signs of regrowth, water damage or odors.


If you see mold, can you remove it using your own resources or should you call in outside help? Typically, it depends on the size of the mold growth.

In its “A Brief Guide to Mold in the Workplace” advisory bulletin, OSHA recommends that when mold growth exceeds 30 square feet in size, “industrial hygienists or other environmental health and safety professionals with experience performing microbial investigations and/or mold remediation should be consulted prior to remediation activities to provide oversight for the project.”

The agency also notes that some states or jurisdictions may require the use of licensed remediation companies and assessment consultants if mold growth is larger than a certain size. So, it’s wise to check local or state regulations as part of a mold management strategy and include them in written procedures.

According to OSHA, no federal standards or recommendations on airborne concentrations of mold or mold spores exist, including from EPA or NIOSH. For mold on walls and other surfaces, OSHA and EPA call for the use of “professional judgment” when deciding how to remediate mold, and each agency has guidelines based on different sizes of mold growth.

“When in doubt, caution is advised,” OSHA says. “Consult an experienced mold remediator for more information.”

Bailey and Park warn that if you suspect your HVAC system is contaminated with mold, or if it’s been confirmed, don’t let it run. They also recommend against duct cleaning “unless it is found to be contaminated with mold or other irritant particles” affecting the occupants of the building.

“Improper duct cleaning can release large amounts of dust and other contaminants, including mold spores, into the work area,” Bailey and Park said. “Fiberglass ductwork that has mold growth must be replaced – it cannot be cleaned. If metal duct cleaning is deemed necessary, it should be performed by contractors who are members in good standing of the National Air Duct Cleaners Association.”

Weekes and Springston suggest avoiding or being wary of companies that offer both mold assessment and remediation.

“There’s an inherent conflict of interest,” Springston said. “We see it, unfortunately, quite a bit, where a company will come in, do an assessment and say, ‘Well, we can fix that and do the remediation for another $5,000,’ or however much. Assessment and remediation should be separate.”

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