We reference the industry standard Bioaerosols: Assessment and Control (1999), published by the American Conference of Governmental Industrial Hygienists (ACGIH). The ACGIH standard is the current authority on biological contamination, and is a practical guide for identifying and correcting suspected sources of microbiological amplification. Several other industry guides have been published in recent years, including:
- Environmental Protection Agency (EPA) Mold Remediation in Schools and Commercial Buildings, EPA 402-K-01-001, March 2001.
- Environmental Protection Agency (EPA) Guide for Building Owners and Facility Managers, ISBN-0-16-035919-8, published in December, 1999.
- Institute of Inspection, Cleaning and Restoration (IICRC), Standard and Reference Guide for Professional Water Damage Restoration, IICRC S500, 1999.
- New York City Department of Health (NYCDOH), Guidelines on Assessment and Remediation of Fungi in Indoor Environments, May 1993, Revised March 2004.
- American Industrial Hygiene Association (AIHA,) Field Guide for the Determination of Biological Contaminants in Environmental Samples 1996.
- American Industrial Hygiene Association (AIHA), Assessment, Remediation and Post Remediation Verification of Mold in Buildings, AIHA Guideline 3, 2004.
As described by EPA and ACGIH, and supported by publications by the American Industrial Hygiene Association and the National Institute of Occupational Safety and Health, the amplification of biological populations should not be tolerated in occupied buildings. The presence of amplification requires mitigation measures to remove the biological growth. Existing industry standards indicate the need to remove affected porous materials, clean affected non-porous materials, and thoroughly clean all surfaces in the area of the contamination. Caution is advised in the use of disinfectants, to ensure that building occupants are not exposed to chemical biocides that can be hazardous with uncontrolled use.
The behavior of moisture in the structure is the critical component of biological contamination. Water infiltration through the skin of the building is a common source of moisture damage. Evaluate the condition of the roof, siding, windows and doors. Inspect for evidence of moisture damage in the areas of these structures on the building interior. Evidence of water damage around doors and windows is frequently in the form of water stains, wrinkled paint and peeling drywall tape. The grading around the building should be reviewed to ensure the water flows away from the foundation. This is especially important in the area of roof leaders and drains.
Perhaps the most common sources of moisture damage in a building are the plumbing systems. Potable hot and cold water lines and sprinkler systems can fail catastrophically, or leak slowly through a pinhole or bad fitting. Potable water is classified as Category 1 clean water, and may not initially support biological growth. If materials can be dried within 24-48 hours, growth may not have an opportunity to commence. It is important to note, however, that if the water comes in contact with an existing fungal condition, additional growth will commence almost immediately.
Leaks from sanitary sewer lines are considered to be contaminated at the outset of the event. Category 2 water is classified as gray water, and includes water from washing machines, dishwashers, sinks, and toilets that did not contain feces. In some cases it may be possible to salvage materials affected by Category 2 water, but the cleaning would have to commence immediately.
Category 3 water is classified as black water and includes water from toilets with feces, sanitary sewer lines, floodwater that has been in contact with soil, and seawater. Porous materials that have been in contact with Category 3 water must be discarded, since it is possible that a number of virulent bacteria may be present in the water. In many cases even semi-porous materials such as wood sheathing and particleboard will not be salvageable.
Basements are a notable location for biological growth due to several factors, including water infiltration through the foundation, plumbing leaks, and condensation on the cold surfaces of masonry walls and floors. It is important to realize that relative humidity at the layer of air along a cold surface will be higher than in the middle of the room. A number of common fungi can thrive on these surfaces if the relative humidity exceeds 70%. It is not uncommon for the cold surfaces to support a biological population that is not readily apparent, until a water event causes the existing population to explode.
Crawlspaces are usually not a significant problem as long as they are reasonably dry and have adequate cross-ventilation. When there is water infiltration and the ventilation is not adequate to remove water vapor, biological growth can develop on the wood joists and on fiberglass insulation in the crawlspace.
The porosity of the materials affected by moisture is the primary consideration is determining whether a material can be salvaged. Porous materials such as carpet, fiberglass insulation and drywall are usually impossible to thoroughly clean and should be discarded. This is especially true in environments such as basements where the biological growth has previously initiated. Pay especial attention to very porous materials such as carpet and insulation. There can be substantial biological activity with no visible evidence. Microorganisms enjoy an environment with depth. In the plush matrix of these materials, moisture conditions are stable and no drying air currents are present.
Semi-porous materials can usually be cleaned and salvaged, unless the water damage has affected the structural integrity of the component. Wood materials such as dimensional lumber, plywood and most finished wood surfaces are reasonably resistant to moisture damage. Composite wood materials such as particleboard, oriented strand board and chip board are much more likely to absorb moisture, develop structural problems and support a biological population within the material matrix.
Hard surfaces such as metal, vinyl and painted masonry can usually be cleaned and salvaged. On some materials there is the possibility of staining from certain fungi types, especially on plastic surfaces that contain the hydrocarbon that the fungi can colonize. Unfinished masonry is classified as semi-porous, and frequently benefits from a spray encapsulation of an antimicrobial sealer after the unfinished surface has been cleaned.
It has become customary to construct a negative pressure containment system to isolate the affected work area from the unaffected living spaces. Polyethylene sheeting is used to cover openings such as doorways, windows and ventilation grills. Negative pressure is established with the use of high volume exhaust units equipped with High Efficiency Particulate Air (HEPA) filters. Entry to the work area is achieved through a primitive airlock comprised of overlapping layers of polyethylene sheeting. The integrity of the containment system is evaluated by measuring the concentration of airborne particles with a direct-reading laser particle counter.
When the containment has been established, the affected materials are carefully removed, sealed in polyethylene bags and transported to the waste vehicles. Materials contaminated with microorganisms are not a regulated waste, and are transported from the site to a landfill as normal construction waste
Cleaning is the final critical activity. The affected areas are wiped clean with a disinfectant cleaner such as Microban Plus, which is a moderate level disinfectant containing quaternary ammonium compounds. The disinfectant is effective against mold and bacteria, but does not leave any harmful residues. The surfaces are wiped until they are clean and dry. Dryness is important, since all disinfectants are in aqueous solution and can be more than 99.9% water.
After allowing appropriate time for drying, all surfaces are cleaned with vacuums equipped with High Efficiency Particulate Air (HEPA) filters. Since the contaminants are microscopic in nature, all visible dust and debris is presumed to contain organisms. The cleaning proceeds until all visible dust is removed, and the surfaces are as clean as practical.
For semi-porous materials such as wood and masonry, it is often beneficial to seal the surfaces with an antimicrobial encapsulant product such as Foster’s 40/20. The encapsulant fills in the surface pores and discourages future colonization. The encapsulant will make the surface more resistant to future mold growth, but will not totally prevent growth if moisture persists in the building. It is important that the water infiltration be corrected prior to reconstruction.
In cases where water activity cannot be fully reduced, it may be necessary to reconstruct with finishes that are resistant to biological growth. In a damp basement, for example, resilient floor tile may be a better choice than carpet. In bathrooms, reinforced cement board has largely replaced drywall as the wall construction of choice.