Microbial Remediation(from the NADCA manual-"Understanding Microbial Contamination in HVAC systems")
Microbial Remediation
(from the NADCA manual-"Understanding Microbial
Contamination in HVAC systems")
Background Information
Mold is the common name given to filamentous fungi. This and other types of fungi
refer to most forms of microbial contamination of HVAC systems. Fungal spores vary in
concentrations in both indoor and outdoor environments. This makes it difficult to
establish limitations for use in comparative studies and evaluations. The detection of
mold in an HVAC system is normal; what makes it a concern in the presence of active colony
growth (amplification).
Any initial indoor air quality investigation should include a survey of the ventilation system, especially those areas that are known for potential amplification. These areas include cooling coils, condensate pans, filters and humidification systems. Amplification can also occur on wet ductwork surfaces, including the lining. Sampling for amplification can stop once the source of amplification is isolated. The removal of any contaminated porous material is often sufficient remedial action. Remediation of the contaminants play a vital role when allergic reactions due to exposure to micro-organisms or an infectious disease has been diagnosed.
Remediation
Before taking remedial action, it is important to identify the contamination
sources and the expected results of the remediation. Remediation techniques for microbial
contamination depend on the surfaces where the contamination exists. Non-porous HVAC
surfaces can be cleaned. However, steps should be taken not only to eradicate the growth,
but to insure its containment during the remediation process. The US Environmental
Protection Agency (USEPA) and the North American Insulation Manufacturers Association
(NAIMA) recommend that any water-damaged porous material, such as insulation,
acting as an
amplifier, be removed rather than cleaned.
Services are provided by a mold remediation specialist certified by the Environmental Assessment Association.
The remediation process consists of 4 elements: Identifying and correcting the source of contamination; Controlling the contaminated area to prevent spreading of fungi; Source removal of the fungi, contaminated dust, debris and other unwanted materials within the ventilation system; and Treating the affected areas with an antimicrobial chemical, if necessary.
Antimicrobial Chemical
Antimicrobial chemicals (biocides) are identified in 6 classes by the Federal
Insecticide, Fungicide and Rodenticide Act (FIFRA). Of these 6 classes, 4 are applicable
to HVAC systems. These classes are: Sterilants, which eliminates ALL forms of
microbial life; Disinfectants, which eliminates infectious pathogenic bacteria;
Sanitizers, which reduces microbial contaminants; and Fungicides, which destroys
fungi that are pathogenic to humans or animals on inanimate surfaces.
In order for the biocides to be effective, the surfaces to be treated must be clean and thoroughly wetted with the biocide. The surfaces should not be wet for more than 24 hours or the moisture may promote new fungal activity. After remediation services the surfaces should be dry. All interior HVAC system surfaces must meet coverage and exposure criteria defined by the biocide manufacturer. The remediation firms should provide the means to insure and verify the results of sanitizing.
The use of biocides must be considered toxic, and as such, exposure must be minimized as much as possible. Workers and building occupants must be protected from short- and long-term exposures.
The Decision to use Biocides
Since fungi is constantly present, air samples and wipe samples will always yield
positive results. The decision to use biocides should be based on a risk assessment
(health risks of exposure to mold amplification) and economics (cost benefits of
remediating the mold).
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