Where Does All the Dirt Go?

Floor covering in schools continues to generate discussion as to what may be best suited for students susceptible to respiratory challenges. Recognizing the trend toward dwindling budgets being allocated to school maintenance and operations, floor coverings that require diligent attention to prevent buildup of contaminants may present a challenge for school officials and maintenance personnel.

Without proper maintenance, dirt can continue to accumulate to the point where the carpet no longer acts as a sink. According to one study, dust resuspension (settled dust that becomes airborne again) can represent an important contributor to airborne particulate matter.

With funding from C&A Floor Coverings, a study was conducted by University of Tulsa’s Indoor Air Program to learn more about particle build up and resuspension potential on two types of floor covering. The study’s objective was to evaluate the characteristics of specific types of floor covering products under both controlled chamber testing conditions and in the field under school-occupied conditions.

The study’s researchers included R. Shaughnessy, Ph.D.; E. Cole, Ph.D.; T. Brennan; W. Turner; B. Turk; R. Smith; and B. Jewett. The study was peer reviewed and presented at an indoor air quality conference in Beijing, China.

“Historically, all carpet was considered the same in terms airborne contaminants and recovery,” says Tom Ellis, vice president of Sales for Dalton, Ga.-based Tandus (C&A’s parent company). Turns out it’s a little more complicated. All carpet is flow-through, meaning it has an open weave backing to allow for the transmission of air, dust, and moisture from the face side to the subfloor. But not all textile floors are non flow-through, which is to have closed cell cushion backings that retain air, dust, and moisture above the backing.

“VCTT is a non flow-through product,” notes Ellis, “that looks like carpet, but it’s just an impression of vinyl tile looking like carpet.” So, for this study, flow-through floor coverings were compared to non flow-through. The flow-through was medium-face weighted carpets; the non flow-through was low- to medium-face VCTT.

In School and Chamber Recovery
Scientific method was applied to establish baseline data related to total recovery of dirt from occupied school carpets. In all, 78 sets of initial recovery data were collected from eleven schools, including high schools, middle schools, and elementary schools in five school districts. The data were separated into two carpet categories (flow-through and non flow-through).

Similarly, scientific method was applied to establish baseline data related to chamber recovery of dirt.

Chamber Resuspension
Next, chamber resuspension tests were conducted following scientific method. Resuspension occurs when walking on the floor covering allows the settled particles to become airborne again. Ellis notes that this is called the “pig pen effect.” Chamber resuspension tests included:

  1. activity on bare clean floor (no carpet) in chamber to establish background;
  2. activity on bare clean carpet sample in chamber to establish carpet shed background (conducted before each test with embedded dirt); and
  3. activity on carpet with predetermined allotments of dirt embedded into carpet (per protocol used in recovery testing).

In School and Chamber Recovery Discussion
Past research has focused on the level of vacuuming necessary to remove dirt that is embedded into a carpeted material; however, few if any researchers have thoroughly investigated potential differences in behavior associated with specific carpet type. The data reflect similar agreement with past research as to dirt removal characteristics by vacuuming (indication of time required to thoroughly clean).

However, there are clear differences noted between the flow-through and non flow-through carpet types. While data from the non flow-through carpet with an impervious cushion backing reflects fairly consistent removal characteristics, data for flow-through carpets is not linearly dependent, probably because of other confounding factors. Factors influencing the removal of dirt from a flow-through carpet may include, but are not limited to:

  • the open weave backing of the flow-through carpet allows passage of debris beyond the product backing providing a reservoir for debris between the carpet backing and the sub-floor (The debris in this reservoir may not be impacted by the rotating brushes of a vacuum cleaner and may extend the required vacuuming time to remove.);
  • deep-cleaning solutions and extraction processes used in schools may result in a residue buildup on the fibers that inhibits the release of the debris that builds up with time (This may impact both types of carpet product to some extent, but may have a greater effect as dirt product accumulates in the backing of the flow-through product.); and
  • the continued buildup of dirt within the flow-through carpet, caused by inadequate maintenance on a daily basis, combined with constant foot traffic through extended periods, may result in embedment of dirt into the carpet (especially in flow-through types where debris can further be lodged in backing matrices).

Resuspension Discussion
Comparison of resuspension data collected in the chamber, related to new non flow-through carpet and new flow-through carpet, revealed elevated levels of particle release from the flow though carpet. Total airborne particles originating from the flow-through carpet indicated release of two to five times more particles than the non flow-through. In addition, there was a marked increase in resuspension as loadings increased.

The face weights (number of ounces of fiber per square meter of carpet) of the compared carpets were very similar for the products sampled in the project. However, the method of attaching the fiber to the backing and the types of backing used are different. In addition, the open weave backing of the flow-through carpet may provide easier release of particles into the air from a new product. More data, in the field and in the chamber, are being collected to further explore these hypotheses.

The Study’s Conclusions

The study demonstrates that carpeted floor covering used in school is not a homogeneous medium and physical characteristics vary based on the type of backing, carpet tufted type, face weight, gauge (including stitches/inch), and adhesive requirements.

In addition, the data suggest that a reduction in particulate matter harbored on/in flooring material may present a decreased risk of airborne exposure to children, dependent on the individual flooring type. This seems obvious but is more complicated. If a floor covering looks clean, it may not be vacuumed as often, notes Ellis. This is fine to the point that the floor covering can contain the dirt. But what happens when the floor covering can no longer contain the dirt? Where does the dirt go?

Also, floor covering that is not cleaned adds to the pig pen effect, allowing particulate to become airborne and breathed in. “Children are closer to the floor than adults,” says Ellis. “They’re more likely to breathe particulate by virtue of the fact that they don’t have an adult’s height.”

More research, as to individual flooring types and dust retention/resuspension characteristics, is needed to further define the impact of flooring and significance of proper maintenance in a school environment.