Water Damage Restoration

Growth of Fungi

To grow on interior building materials, fungi require nutrients or substrates, warm temperatures and, most of all, adequate moisture. Nutrients or substrates can be as diverse as vinyl wall carpeting adhesive, the paper surface of gypsum board, cellulose-based ceiling tile and accumulations of dirt and dust in carpet. Building interiors which are moist provide an ideal environment of fungal proliferation.

Construction and design defects in the buildings studied allowed moisture to enter by water leakage, air infiltration, vapor migration and cooling coil bypass. Water leakage can occur due to roof leaks and leaks around window framing. If a building is negatively pressured relatively to the outdoor air, especially in hot humid climates, moisture will infiltrate through open doors and around windows, through exhaust vents and through loose construction. In buildings in coastal areas of the southeastern United States, humid outdoor air can migrate through concrete block walls into interior spaces if a vapor barrier on the exterior surface of the concrete block is absent or incomplete. Also, air handing units may move outdoor air too rapidly through cooling coils for adequate removal of moisture present in outdoor air entering the ventilation system.

Some fungi begin to grow when the relative humidity of the air inside a building exceeds approximately 70%. Of greater importance, however, is the amount of water available for fungal growth in a building material, also called its equilibrium relative humidity (ERH). Because of their different abilities to absorb and to tightly hold water, various building materials can have the same ERH but very different moisture contents. For example, at an ERH of 80% (adequate to support the growth of Aspergilius varsicolor, but not Stachybotrys), the approximate moisture content occurs in the following construction materials:

Gypsum (sheetrock) - 0.7%
Wallpaper - 11.3%
softwood - 17%

Some fungi are able to grow in ERHs that are less than 60%.

Steps for Remediation

  1. Isolation of each work area by enclosing it in a double-layer of plastic sheeting
  2. Maintenance of negative air pressure differential inside the enclosed work area relative to the outside areas by use of air filtration devices (AFD) equipped with high efficiency particulate air (HEPA) filters.
  3. Respiratory and skin protection for workers entering the work area.
  4. Double-bagging of microbial-contaminated building materials before removal from the work area.
  5. Use of HEPA vacuums to clean work area surfaces of bags containing contaminated materials.
  6. Compliance air sampling for fungal spores both inside and outside the work area following completion of remediation to demonstrate that fungi had been removed and that spores had not been released into occupied areas during the remediation activity.

Important Note

If remediation of microbial contamination is not handled with the proper precautions, remediation workers and building occupants can be exposed to harmful concentrations of fugal spores and contamination can spread to other parts of the building. A building owner should work with a professional who is knowledgeable of the hazards of microbial contaminants to assess the extent of contamination and to develop specifications for remediation.

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