Poor indoor air quality in school facilities can detract from the health and productivity of students, teachers and other employees. Asthma — often triggered or aggravated by dust — is the No. 1 cause of chronic absenteeism in schools.

Using vacuum cleaners equipped with HEPA filters to clean education institutions can help school maintenance workers combat indoor air quality problems. The filters, which capture particles through layering and brain-like folds or corrugations, enable vacuum cleaners to keep dust inside the machine rather than spreading it throughout the indoor environment.

HEPA has not been without its critics, however. They are far more expensive than standard filters, and because of the finer mesh and greater resistance to airflow, they may reduce a vacuum cleaner's suction and performance. In many uncontrolled and non-critical environments, the benefits of HEPA filtration are negated by particles entering the air from other sources, such as an open door or window.

Generally speaking, though, HEPA filtration is a useful tool for school maintenance programs.

Common terms

HEPA (high-efficiency particulate air) is a technical definition that refers to a filter “that will remove not less than 99.97 percent of 0.3 micron diameter particles or larger from the air that passes through it.”

HEPA filters were developed in the 1940s to capture radioactive dust. The research for HEPA filters, originally called “absolute filters,” was part of a U.S. government contract related to the Manhattan Project that developed the nuclear bomb.

Over the years, HEPA filtration has become more commonplace. Besides vacuum cleaners, it is used in high-tech manufacturing and cleanroom applications such as pharmaceutical, photographic, computers, optical, healthcare, food processing and aerospace.

HEPA-filtered vacuum cleaners are especially useful in healthcare applications where dust can contain microbes such as Aspergillus, a mold that can cause infection in patients with weakened immune systems.

Some other useful filter definitions:

  • True HEPA means the entire vacuum system in which the HEPA filter is mounted is airtight (except where air properly enters and exits the vacuum), thus preventing dust-laden air from escaping through gaps in the vacuum body or around the filter seal. Theoretically, it also means the airflow of the vacuum has been proportioned properly for the HEPA filter media, so that what exits the filter meets the 99.97 percent at 0.3 micron efficiency benchmark during use.

  • Sealed HEPA refers to a vacuum system that is sealed so that all the air being drawn into the vacuum goes through the HEPA filter. In some cases, the term refers to only the filter itself being sealed at the filter mount.

  • Near-HEPA describes filtration systems that filter near, but do not meet the level of particle capture required for HEPA filtration. In some cases, the tradeoff is worth it, since near-HEPA filters cost only a fraction of what true HEPA costs.

  • ULPA (ultra-high efficiency particulate air) is a technical definition that refers to a filter that will remove “not less than 99.999% of 0.12 micron diameter particles or larger from the air that passes through it.”

  • Multi-Stage filtration describes a system that uses multiple layers of filter material to remove particles of soil. These can be used alone or as a pre-filter for HEPA, ULPA or other filtration systems.