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Airborne Mold

By Michael Hilton

Airborne biologicals, particulates, and volatile organic compounds (chemicals) primarily affect indoor air quality. Biologicals include bacteria, fungi, and allergen. In many areas of the country, the primary concern among indoor air quality (IAQ) specialists has been airborne fungi levels, because fungi includes both allergenic species and toxigenic species that can produce serious illness or even death.

Airborne fungi can be found in every environment, indoors or outdoors at various levels. Mold (fungi) spores are present, daily, in the air we breath. As a result of deposition from the air, fungi can be found on every horizontal surface at various levels. While no acceptable or unacceptable standards for culturable fungi have been established, some IAQ consultants have begun to evaluate various surfaces such as carpet, draperies, and upholstered furniture to establish IAQ impact, based on prior data history. In essence, without having established the level at which health concerns become evident, consultants identify high or low accumulations based on the levels found in other environments in the past. This procedure is based on the "assumption" that higher fungi levels have contributed to IAQ complaints without establishing a direct correlation.

Carpet Becomes Easy Target

Using this rationale, carpet has become an easy target for IAQ professionals because of the ease in which dust samples can be collected and evaluated. Dust samples are evaluated for fungi content based on colony forming units (cfu) per gram of dust. IAQ impact is sometimes evaluated by levels found in these dust samples. This procedure suggests that carpet is the source for airborne fungi, rather a result of airborne concentrations that have settled to the carpet surface through deposition.

Without establishing a direct correlation between airborne levels and fungi levels in carpet dust, IAQ consultants routinely recommend carpet removal. However, carpet removal rarely resolves IAQ complaints, because carpet is rarely the source of the complaints.

Recently, several large school districts in the northeastern U.S. and the southeastern U.S. were evaluated for IAQ complaints. In each district, approximately one-third of the schools had received complaints attributed to poor indoor air quality. A similar number of complaint schools contained VCT and carpet, yet in the carpeted complaint schools, poor IAQ was attributed to carpet. In the VCT schools, the complaints were attributed to "other unknown cause" This deduction was based on the unsubstantiated "common perception" that carpet was a contributor to the IAQ complaints rather than direct scientific evidence. Two of the districts entirely replaced carpet with hard surface flooring materials. IAQ complaints increased significantly in these schools, due to other psychological factors such as muscle fatigue, higher noise levels, and higher dust levels found with hard flooring surfaces.

Other factors, related to hard flooring, were involved in the decision to replace the carpet. The misperception that VCT was easier to maintain, led to reduced maintenance and increased airborne soil and allergen levels. In essence, VCT was not easier to maintain, just easier to neglect!

Air Quality = Complex

Indoor air quality is an extremely complex mix of variables and by attempting to address individual components, such as carpet installation or removal, we are no closer to resolving air quality complaints. Environmental factors such as temperature and relative humidity, interior soil levels, chemical odors, noise levels, moisture intrusion, occupants per square foot, fresh air ventilation, and many other factors affect indoor air quality.

Recent studies have begun to evaluate the impact of these variables on IAQ and a number of studies are beginning to challenge the perception that carpet affects indoor air quality. In two recent Florida classroom studies, the efficacy of carpet cleaning was evaluated to establish the effectiveness in removing biologicals from carpet. In accepting the assumption that biologicals in carpet contribute to airborne biological levels, a reduction in carpet biologicals should produce a reduction in airborne levels and reduce IAQ complaints. However, reduced biological levels in carpet over a sustained period had no impact on airborne biological levels.

The first study, performed in Miami schools, evaluated biological reduction only, using five accepted carpet cleaning methods. Each method reduced biological levels significantly with wet extraction reducing levels by more than 99%.

The second Florida school study, performed in Tampa area schools, evaluated the long-term influence of regular carpet care and reduced carpet biologicals on airborne biological levels. This second study affirmed that biologicals in carpet could be reduced by 99% with wet extraction cleaning. A continuing carpet care program continued to reduce biological levels in carpet over the course of the study, but airborne biological levels were unaffected. It was established that, in most instances, outdoor fungi levels play a far greater role in indoor fungal levels than interior furnishings.

While it has been assumed that airborne fungi levels can provide insight into possible air quality complaints, there are no acceptable or unacceptable standards for airborne fungi. It is the type, rather than the level, of airborne fungi that establish health effects. One study evaluated the impact of airborne fungi levels, humidity levels, and reported health complaints.

This study, performed by Racine Industries, established that humidity levels and other environmental factors, may play a greater role in perceived health complaints than actual airborne biological levels.

The study evaluated both complaint and non complaint classrooms and found that complaint rooms had higher humidity levels and lower airborne fungi levels than non-complaint classrooms.

As a result of these astonishing findings, studies were performed to evaluate the influence of humidity levels on biological growth in carpet and the capability of carpet to contain these contaminants without airborne release. Because field studies are difficult to distinguish between biologicals introduced via the ventilation system and biologicals released from carpet, the study was performed in an environmental chamber. In this environmental chamber study, heavily contaminated carpet was obtained from a south Florida school and incubated at two different humidity levels (55% and 90%) for four weeks. Each carpet was placed in the environmental chamber and complete air and surface sampling was performed. Activities such as walking, vacuuming, and carpet cleaning (5 methods) were monitored.

Ultimately, this study affirmed earlier findings of the efficiency in biological removal from carpet as a result of wet extraction cleaning, but also it demonstrated that carpet does not release airborne biologicals held within the pile, despite heavy biological contamination. While no "active" growth was found on the surface of the "normal" humidity carpet, the high humidity carpet (90%rH) revealed active biological on the carpet surface.

It is unreasonable to expect any flooring surface to be maintained free of biologicals. However, by maintaining an environment within an acceptable humidity range, problems related to active biological growth can be minimized.

Other flooring surfaces can provide an equal opportunity for biological growth and due to accepted maintenance practices, biological levels can be increased significantly. Hard surface flooring systems do not provide an acceptable extraction method of cleaning. Contaminants must be extracted and removed from a facility to accomplish effective cleaning.

In several studies in which the cleaning of VCT was evaluated, biological levels were actually increased as a result of normally accepted maintenance practices. To ensure adequate biological reduction, wet mops should be laundered daily. Cotton can be a food source for biologicals.

Allowing a wet contaminated mop to remain in a custodial closet overnight encourages biological growth. Additionally, mop solutions should be replenished after every 1500 square feet to limit cross contamination. Unfortunately, while these recommendations limit biologicals, they are seldom performed due to the amount of time involved in rinsing mops and replenishing solutions.

Conclusion

  • Biologicals, particulates, and volatile organic compounds affect indoor air quality.
  • Airborne fungi can be found in every indoor environment.
  • There are no acceptable standards for indoor fungal levels
  • Without establishing levels at which health concerns become evident, it is impossible to identify high or low fungal concentrations.
  • Humidity levels play an important role in allergy complaints. It is the type of fungi rather than level that establishes health effects.
  • Carpet removal rarely resolves IAQ complaints
  • A like number of IAQ complaints occur in carpeted and non carpeted environments.
  • Carpet does not release fungi held within its pile into the breathing zone.
  • Wet extraction reduces fungal content in carpet by greater than 99%
  • Environmental conditions may have a greater effect on IAQ than airborne fungi levels.
  • It is unreasonable to expect any flooring surface to be maintained free of biologicals.
  • Carpet must be returned to a dry state within 12 hours to arrest fungal growth.

About the Author
Michael Hilton was the original creator of Carpet Buyers Handbook. Having owned and operated a carpet wholesale company, Hilton has a vast knowledge about all-things carpet related as well as other types of flooring.

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