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.
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.
Is it or isn't it?
From a practical and technical standpoint, if the air leaving a vacuum cleaner contains more than .03 percent of 0.3-micron diameter particles, it is not HEPA filtration. For genuine HEPA filtration to occur, the filter must be sized and sealed properly, and contain the right media.
This can be confusing because manufacturers test their equipment and explain their results differently. For example, some companies test only the air going through the filter, but not the air coming out of the motor exhaust or through gaps in the body or around the motor housing and wheels. Some manufacturers test their vacuums in a closed chamber, which tests all the air coming from the machine. Other manufacturers use different methods to test their vacuums and filters, and some do virtually no testing at all.
Because not everyone follows the same rules, many manufacturers make similar-sounding but different claims to market their vacuum cleaners and filtration, with little standardization and regulation.
How do education institutions know what they are getting? Facility managers should ask questions, check references and require manufacturers to provide copies of independent test reports that validate filtration, airflow and efficiency claims.
HEPA today, gone tomorrow?
All filter systems require ongoing maintenance or they will become “loaded,” clogged and ineffective. A clogged filter doesn't filter properly, reducing the airflow through the vacuum cleaner and limiting its ability to pick up soil. A clogged filter also makes the vacuum motor work harder.
HEPA filters need to be replaced — or, in certain cases, cleaned — when loaded. How often they need replacement depends on the level of use, pre-filter maintenance and the manufacturer's recommendation. Vacuums with HEPA filters for critical environments — such as cleanrooms where microchips are made — must be tested regularly using an established procedure.
Some companies sell portable laser particle counters for onsite monitoring. These can be useful for checking particle counts coming from various parts of a vacuum. Costs can range into the thousands of dollars; however, prices are falling.
Not all filters are of the same quality. Some manufacturers assert that generic filters do not work in their machines as well as their own filters and have less than optimum media, thus allowing contaminated air to get out of the vacuum and into the environment.
Selection and maintenance
A HEPA media filter can be a viable addition to a vacuuming program. A properly sized and fitted HEPA filter removes 99.97 percent of particles 0.3 micron and larger; this is useful in buildings where occupants are hypersensitive to even small amounts of airborne dust.
The HEPA media filter should be proportioned for the vacuum's rate of airflow or air velocity — airflow must be carefully matched to the volume of filter material and size of the filter. If there is too much airflow and too little filter media — a common problem with some machines labeled “HEPA-type” — then filtration efficiency drops.
A good seal at the filter mount and in the vacuum body is essential. Without it, air pressure will force dust through gaps and into the air.
The inline filters preceding a HEPA filter in the airflow path should be of good quality and properly maintained — emptied and cleaned or replaced regularly. A first-stage filter (typically a disposable bag) of poor quality, or one that overloads and tears, will pass dust and load the HEPA filter quickly, requiring premature and expensive HEPA filter replacement. A loaded HEPA filter will impede airflow, reduce cleaning performance and often overheat the vacuum motor. Cleaning and maintenance of the filter media will ensure consistent airflow for sustained performance and long vacuum-motor life.
Rathey is president of InstructionLink/JanTrain, Inc., Boise, Idaho.