Few cleaning processes are as important to IAQ as vacuuming, and few internal steps are as important to the process as vacuum filtration. Without proper filters to catch dust, fine particulate is blown through the filter media and into the ambient environment. A vital factor to assess in choosing a vacuum filter is both the size of dust particles-measured in microns--and the quantity of dust particles removed from the vacuum's airflow.

A micron is one millionth of a meter, 1/70^th the thickness of a human hair. Single dust particles smaller than 10 microns are so tiny they are virtually invisible. When the main interest was in removing visible dirt, traditional cloth or paper bags filtering down to 10 microns were widely used. Vacuums that could effectively remove particles smaller than that were considered specialty items-valued only for stringent applications like computer data centers. Now homes and buildings are "tighter"-with less air exchange to dilute airborne dust-and people are reacting to the respirable particles (mostly ranging between .3 -10 microns) they are breathing in energy efficient dwellings.

Statistics indicate 50 million Americans suffer from allergen-related diseases. Many allergic reactions are caused by airborne carpet and upholstery fibers, pet dander, molds, spores, bacteria, and dust mite feces, dispersed by inefficient vacuuming. While newer filters remove fine dust, the critical question is, how much fine dust is captured? Less desirable filter arrangements may capture only 30% of one micron particles, while better filter configurations enable removing 99% or more of those particles. That brings us to the issue of filter efficiency.

"Filter efficiency"--expressed as a percentage-denotes how much dust of a particular size a filter captures. For example, a filter that is 95% efficient at one micron, catches 95% of all particles that size. By contrast, an advertised "1 micron filter" (capable of removing particles as small as 1 micron) may be retaining only 30 percent of all 1 micron particles, while the remaining 70 percent pass through the filter and escape. That filter would have a 30 percent efficiency rating at one micron. Conversely, if the filter arrangement removed 99 percent of all 1 micron particles, it would have an efficiency rating of 99 percent. Typically, old-style cloth bags have an efficiency rating of only about 30 percent at one micron.

Airflow and lift create suction, traits relating closely to effective filtration, since dust must be adequately pulled into the filter's mesh without being pulled through the media by too much pressure. An integral part of the vacuum's operating system, filters are only effective when they are carefully proportioned to the airflow and lift created by the vacuum motor's fan. The filter media is also critical since material that catches fine dust must "breathe"--letting air pass through-to create sustained suction and cleaning ability. As you can imagine, developing materials that trap the finest dust while sustaining airflow is the goal of vacuuming engineers. Fortunately, there are several successful filter options that meet this need, depending on the intended application.

In the past, when the main concern was the removal and capture of "large" visible debris and dust, old-style cloth or paper bags were considered adequate. However, with the current emphasis on IAQ and wellness, a higher degree of filtration, usually in the form of layered micro filter media (this media is now used by a number of manufacturers of vacuum cleaners)-high-efficiency filters of several layers-is necessary to effectively remove and retain contaminants down to 1 micron and smaller. Micro filters greatly increase vacuum efficiency.

One study showed that a micro filter in a four-stage configuration removed 95% of one micron debris. Newer micro filters are even more efficient.

More sensitive vacuuming applications require high-efficiency particulate air (HEPA) or ultra-low penetration air (ULPA) filters.

More costly than standard or micro filter bags, both HEPA and ULPA filters are designed to remove more than 99 percent of superfine particles. HEPA filters remove 99.97 percent of particles .3 micron and larger in size. ULPA filters are even more efficient, removing 99.999 percent of .12 micron and larger particles. Both-typically installed as secondary filters "behind" primary filters that catch larger "gross" dust--rely on numerous brain-like folds or corrugations of filter media creating tremendous surface area in a relatively small package to trap fine contaminants without substantially restricting airflow.

Watch out for ads for HEPA filtration, however, since many manufacturers' claims are nothing more than marketing hype. True HEPA filtration requires balancing sufficient filter media with vacuum airflow, along with a proper seal so that dust isn't leaking from other places in the vacuum.