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Airborne Particles

By Michael Hilton

Indoor air is made up of numerous airborne particles including bacteria, fungi, allergen and other nuisance dusts. In a typical indoor environment such as a home, school, or workplace, particle levels are influenced by occupant activity, interior maintenance practices, the quality of interior maintenance, and even the make-up of outdoor air that is brought into the facility by the ventilation system. The study of indoor air quality is a fairly new scientific discipline and the impact of interior particulate levels is only now being researched. Some researchers believe interior furnishings may play a role in these airborne particle levels.

Porous surfaces such as carpet have been examined as a possible source for the introduction of indoor particle levels. Much of the information available with regard to blaming carpet for these interior particle levels is based on opinion or anecdotal evidence rather than direct scientific evidence.

In 1970, using a similar anecdotal thought process which attributed the significant rise in allergies in Sweden to carpet usage, the Swedish Government banned the use of carpet in all public facilities. Carpet was attributed as the primary cause for a number of unexplained indoor air quality concerns. During the next 17 years, carpet sales declined more than 75%, while the sale of hard surface flooring materials increased significantly. By the late 1980, hard floors made up a significant portion of all flooring materials in Sweden. Unfortunately, the incidence of reported allergy symptoms among Swedes increased proportionally with the use of hard flooring materials. The incidence of allergy complaints among Swedes increased more than 300% during this 17-year carpet ban. Swedes quickly learned that replacing carpet with hard surface flooring materials did not prove to be the panacea that was expected. In fact, some Swedes began to blame hard surfaces for the increase in allergic disease because hard surfaces do not provide the capability to trap particles and prevent their airborne release.

The presence was soil/particles in carpet does not necessarily identify carpet as the source for these airborne particles. In fact, a number of studies indicate that the presence of soil/particles in carpet may indicate the opposite. According to Dr. Alan Hedge (Department of Design and Environmental Analysis, Cornell University, Architectural Review) Ӆthe fact that carpet may collect more lint and dust than a tiled (hard surface floor) surface may be considered an advantage, as it is better to have dirt and bacteria-carrying particles held down in the carpet until it is vacuumed, than to have it stirred up and airborne by continual shuffling of shoesءs in the case with smooth surfaces.Ԡ

Recently, a study was initiated to compare the differences in airborne particle levels above carpet and hard surface flooring materials. Two adjacent portable classrooms were selected in a Florida school that had reported air quality complaints in other permanent classrooms on the campus. A classroom with seven-year-old carpet and 28 students was selected and an adjacent one-year-old classroom with VCT with 17 students was selected. Despite a higher, student population and longer use life, the carpet classroom had a lower airborne particle concentration. The VCT classroom had average levels that reflected outdoor levels while the carpet classroom actually revealed lower levels than those found outside. Additionally, peak particle were significantly higher in the VCT classroom. This is possibly related to the inability of VCT to contain particles lying on the flooring surface. The Carpet and Rug Institute, Carpet and Indoor Air Quality, Technical Bulletin, March 1998. One of the benefits that carpet provides is itsÒ ability to hold particles that have been deposited from the air, where they remain until they can be extracted and removed from the facility. As carpet fills with particles, it loses its ability to trap particles and carpet begins to assume the properties of a hard flooring surface, which has no capability to contain particles.

The Frank Porter Graham study (Indoor Environment Characterization of a non problem building: Assessment of Cleaning Effectiveness, March 1994) confirmed carpetsÒ unique ability to reduce airborne particles. In the study, the carpet was evaluated for dust mass content and cleaned. Airborne particle levels were monitored before and after carpet cleaning. Results revealed that dust mass in carpet was significantly reduced through carpetcleaning. Airborne particle levels dropped following carpet cleaning, but carpet dust mass quickly returned to pre-clean levels. This is possibly attributable to deposition of airborne particles and could be due to the electrostatic properties of carpet.

Carpet Maintenance Activities

The process of vacuuming carpet has been thought to introduce significant particle levels but available testing proves this is not necessarily the case. On the other hand, maintenance activities for hard floors such as burnishing or dust mopping contribute significant particle levels into the facility. The process of burnishing alone contributes more than 10,500 Ö§/m3 according to recent data. Carpet maintenance activities should contribute less than 100Ö§/m3 an indoor standard.

To fully confirm carpets ability to contain particles, studies were undertaken to evaluate the amount of particle generation contributed by carpet. In these environmental chamber and field studies, carpet was evaluated for fungi and dust mite allergen release.

In the first study, performed in an environmental chamber, 10 heavily contaminated carpets were obtained from a contaminated south Florida classroom. The carpets were incubated at 60% relative humidity and 90% relative humidity for 28 days. Five carpet cleaning methods were employed, along with various occupant activities while air samples were collected.

Biologicals and Pile Fiber

After incubation at normal humidity levels, the normal carpet looked typical, while the high humidity carpet revealed significant biological growth on the surface pile. The results showed that the carpet incubated under typical humidity levels did not release biologicals into the breathing zone, while the high humidity carpet released those biologicals that were readily growing on the carpet surface. The results suggested that biologicals held within the pile fiber are not released into the breathing zone, while those growing on the surface produced an effect similar to hard floors where it is readily available for airborne release.

Studies performed in the field support these findings. While field studies are less reliable than environmental chamber studies for airborne fungi, the evaluation of airborne mite allergen provides a good indicator of carpet containment properties.

In this study, dust mite allergen mass contained in carpet was evaluated and found to be in the Ô¥xtremeÔ range, according to the accepted evaluation scale. (see mite allergen exposure). Airborne samples were measured at four inches, twenty-four inches, and forty-two inches simultaneously at three sample sites.

Three activity periods were evaluated including children engaged in vigorous activity, vacuuming with a vacuum cleaner without a dust containment system, and normal vacuuming. Results revealed that no airborne mite allergen was detected at any height during the children rigorous activity period. Airborne allergen was detected during the vacuuming activity, which involved no dust containment system. No airborne allergen was detected during the normal vacuuming activity. This suggests that carpet does a remarkable job of holding contaminants trapped within its pile. With the airborne allergen detected during vacuuming, the results suggest vacuuming also is extremely effective in removing this allergen.

While the data suggests carpet provides a benefit in reducing the amount of airborne particle levels, at the very least there should be no difference in particle levels for the various types of flooring systems. The fact that carpet contains considerable particle mass within its pile, the data does not support beliefs that this presence negatively affects indoor air quality.

Did you know?

Carpet does not contribute to airborne particle levels and some data suggest that carpet may reduce airborne particle levels by absorbing these airborne particles and removing them for the breathing zone. In buying a vacuum cleaner, use the CRI Vacuum cleaner rating program to buy a vacuum that removes soil, offers good particle filtration, and does not damage your carpet fibers.

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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