The report, which quantifies some common indoor activities, appears in the Environmental Science and Technology, a peer-reviewed journal of the American Chemical Society.
Kicking Up Dust Particles
Particles can accumulate in the respiratory system and aggravate health problems like asthma. Homes are filled with these particles, which often come from outdoors, cooking, smoking, heating equipment and, according to the study, dust kicked up from human activities.
"I measured concentrations of airborne particles continuously while performing a variety of normal human activities that resuspend house dust in the home," says Andrea Ferro, Ph.D., a professor of engineering at Clarkson University in Potsdam, N.Y. She did the work as part of her dissertation research at Stanford University.
Ferro and her coworkers placed particle detectors in a house in Redwood City, CA, and then they folded clothes, dusted, made beds, vacuumed and did other everyday activities -- not to mention some less common ones, like dancing. They applied a mathematical model to estimate the strength of each source.
Carpets Are a Big Source
Dusting, of course, kicked up a significant amount of particles, but it wasn't the biggest contributor. "The highest source was from two people just walking around and sitting on furniture," Ferro says. This released particles at a rate of almost two milligrams per minute -- about half as much as smoking a cigarette.
Dancing on a rug emitted as many particles as dusting, which wasn't too surprising, Ferro says, since dancing is a vigorous activity. "The source strengths depended on the number of persons performing the activity, the vigor of the activity, the type of activity and the type of flooring," she says. Dancing on a wooden floor was near the bottom of the list.
Not only did Ferro design the study, but she also performed the activities. What kind of dance did she do? "Probably best described as solo salsa," she says. "Luckily, I did not take any videotape."
Vacuuming Releases Deep Dust
Vacuuming was also a large source of particles. Vacuum brushes release deeply embedded particles from the carpet; the motor produces additional particles; and the bags are not 100 percent efficient in collecting particles, Ferro says. Only one type of vacuum was tested; different cleaners could produce different results, depending on the design.
"The result that was most surprising to me was that just walking around can resuspend almost as much dust as vacuuming," Ferro says.
The majority of the particles were larger than five micrometers in diameter, but smaller particles still played a significant role. "Smaller particles tend to deposit deeper in the lungs than the larger particles, potentially causing more harm," Ferro says. The U.S. Environmental Protection Agency classifies these as "fine particles," which have been associated with increased respiratory disease, decreased lung functioning and even premature death.
Tracking Dust From Outside
The results could help people make a variety of decisions about living in their homes. "One study estimates that about two-thirds of house dust is tracked in from outdoors," Ferro says. "Therefore, leaving shoes at the door can make a big difference in reducing the particle reservoir on the floor." She also recommends leaving windows open while cleaning to increase ventilation; limiting the use of toxic household products, like pesticides; and installing non-carpet flooring.
Ferro has since performed another study in a different home, with similar results. "My focus now is to determine the actual mechanisms for resuspension from human activity and perform the work in an indoor air chamber where I can control more of the variables," she says.
