How to Select a Top-Quality HEPA Vacuum

Feb. 7, 2002
HEPA vacuums are used in many industries where the inhalation of microscopic particles can pose a health risk. This guide can help you make the right choice of equipment.

For a filter to be certified high-efficiency particulate air (HEPA), it must be tested and proven to filter particles as small as 0.3 microns to 99.97 percent efficiency at its designed air flow. To appreciate what a HEPA filter does, it helps to understand that a micron is 1 millionth of a meter. A human hair is approximately 100 microns wide. Particles smaller than 10 microns are not visible to the human eye. A particle of tobacco smoke averages 0.01 to 1 micron. Most bacteria range from 0.35 to 10 microns. Almost all viruses, however, are smaller than 0.03 microns, and HEPA filters are not effective.

One of the earliest successful uses of portable HEPA vacuums was their employment in the asbestos abatement industry from the late 1950s to the present day. Portable HEPA vacuums also proved useful for asbestos brake removal at auto repair shops. Next came lead paint abatement projects in public housing and government buildings.

Today, HEPA vacuums are employed in a variety of industries to address the safety and health of workers and residents in any environment where the inhalation of microscopic particles can pose a health risk. One of the most widespread uses of HEPA vacuums is in the duct cleaning service industry, where the recovery of mold spores and other dangerous particles is critical. The latest challenge is the threat of biological or chemical attacks against unsuspecting populations.

What Makes a High-Quality HEPA Vacuum?

Not all HEPA vacuums are of equal quality. There are some guidelines to follow to help get the best quality vacuum for the price. Much of this applies to getting good value in a vacuum. Starting from the ground up, look for high-quality ball bearing wheels and casters that are of sufficient size to be easily moved over irregular floors and up and down stairs. Next, examine the construction of the collection devices for ease of cleaning and disposal of contaminants. Look for smooth, easily wiped surfaces like stainless steel and aluminum. Plastic surfaces should be smooth and free of texturing.

Next, examine the power source - the motors. Better quality electric vacuums utilize bypass, or two-stage, motors. Lesser quality vacuums use single-stage motors. Here's the difference: A bypass motor is made so the motor chamber is isolated from the impeller chamber. The impeller is the fan that creates the lift and suction that the vacuum produces. The motor chamber has a cooling fan that uses clean air from outside the vacuum head to keep the motor and its carbon brushes cool. A single-stage motor uses the airflow generated by the impeller to cool the motor. In a single-stage motor, any particles that escape the filter media are blown into the motor chamber, reducing the life of the motor.

Finally, check the prefilters used on the vacuum. There should be multiple layers of prefiltration to remove as much contaminants as possible before they reach the HEPA filter. Effective prefilters extend the life of the HEPA filter and help reduce operating costs. Good-quality HEPA vacuums utilize three and even four prefilters in some cases.

Comparing Performance Ratings

When comparing vacuums, two performance ratings should be evaluated - static lift and air displacement. Many buyers make the mistake of comparing horsepower or wattage when shopping for a good vacuum. The speed of the motor, number of motors and the design of the impeller have more to do with the performance of a vacuum than horsepower or wattage. Some vacuums are designed to produce high static lift - the ability of the machine to get heavier materials like liquids or metals in motion. Static lift is measured in inches of water or mercury. Others are designed to displace large amounts of air, measured in cubic feet per minute (CFM). These machines are best for recovery of light particles such as bacteria, pharmaceutical dust, lead paint sanding dust, asbestos fibers and so on. Electric vacuums are usually

designed for high lift or high flow. Pneumatically powered vacuums, however, can be made to produce a high level of both performance characteristics.

The Proof Is in the Filters

Early in the incorporation of the use of HEPA filters in portable vacuums, the HEPA filter was simply attached to the exhaust port of a conventional vacuum. In many cases, the HEPA filter was necessarily undersized for its intended purpose. As the vacuum industry matured in its use of HEPA filtration, some manufacturers positioned the HEPA filter on the inlet side of the power source, while some chose to stay with the filter positioned at the exhaust side.

What is best? The debate on this is inconclusive. Positioning the HEPA filter on the exhaust of the power source on an electric vacuum provides the ability to filter carbon dust expelled by the motor brushes, but also allows contaminated air to come into contact with the motors. In addition, the issue of filter leaks is more critical when the filter is positioned on the exhaust, as the filter is always in a positive-pressure mode. When the HEPA filter is installed on the intake side of the motors, the motors are better protected from contamination, and the issue of filter leaks is lessened due to the filter being in a negative pressure-mode during operation.

It is also important to compare the size of the HEPA filter used in each machine. It stands to reason that the larger the filter, the longer it will perform between filter changes. Make sure the HEPA filter is certified at the air displacement that the vacuum generates. If the filter is certified at a lower CFM air displacement than the vacuum generates, it will not perform at 99.97 percent efficiency. Interestingly, HEPA filters actually become more efficient during their life span because the passages between the glass fiber filter medium reduce in size as the filter captures particles.

True HEPA vs. HEPA-Type Filters

"True" HEPA filters must be individually tested and certified to meet 99.97 percent efficiency at the 0.3 micron performance level. Each filter is subjected to a DOP test in accordance with Military Standard MIL-STD-282. DOP (dioctyl phthalate) is an oil that is used to create a smoke with a very narrow particle size distribution. The particle size selected is 0.3 microns in diameter. Following the test, each filter that has passed is assigned a serial number, and the test results are recorded on the filter. If you are looking at a vacuum without this information on the filter, it is not a true HEPA vacuum.

HEPA-type filters are not subjected to the same rigorous testing as true HEPA filters and range in efficiency from 85 percent to 95 percent. Obviously, these units are less expensive than true HEPA units, but their filtering capability is not known exactly. Spending a few dollars more is easily justifiable when health and safety concerns are factored in.

Another Important Feature

Lower-tier vacuums do not provide for a means to determine when it is time to replace the HEPA filter, causing the user to rely on guesswork. Unfortunately, this often leads to too frequent or too infrequent filter replacement. Too frequent replacement is just a waste of money, while too infrequent replacement results in a period of time where the vacuum is used at less than ideal efficiency.

Look for machines that incorporate a device that tells the operator when to change the filter. Some models use a manometer to monitor the HEPA filter's performance, while others use pressure differential devices that measure the pressure drop across the filter and give the operator a signal, such as a light, when it is time to replace the filter. These features may add a little to the initial cost of the machine, but usually result in lower long-term cost of ownership.

As you can see, purchasing a HEPA vacuum is not a decision to be taken lightly. Many factors must be weighed and features compared, but armed with the right knowledge, it is a decision that can be made with confidence.

About the author: Steve Spielmann is the quality assurance/technical manager for Goodway Technologies, Stamford, Conn. He can be reached at (800) 370-2855.

About the Author

EHS Today Staff

EHS Today's editorial staff includes:

Dave Blanchard, Editor-in-Chief: During his career Dave has led the editorial management of many of Endeavor Business Media's best-known brands, including IndustryWeekEHS Today, Material Handling & LogisticsLogistics Today, Supply Chain Technology News, and Business Finance. In addition, he serves as senior content director of the annual Safety Leadership Conference. With over 30 years of B2B media experience, Dave literally wrote the book on supply chain management, Supply Chain Management Best Practices (John Wiley & Sons, 2021), which has been translated into several languages and is currently in its third edition. He is a frequent speaker and moderator at major trade shows and conferences, and has won numerous awards for writing and editing. He is a voting member of the jury of the Logistics Hall of Fame, and is a graduate of Northern Illinois University.

Adrienne Selko, Senior Editor: In addition to her roles with EHS Today and the Safety Leadership Conference, Adrienne is also a senior editor at IndustryWeek and has written about many topics, with her current focus on workforce development strategies. She is also a senior editor at Material Handling & Logistics. Previously she was in corporate communications at a medical manufacturing company as well as a large regional bank. She is the author of Do I Have to Wear Garlic Around My Neck?, which made the Cleveland Plain Dealer's best sellers list.

Nicole Stempak, Managing Editor:  Nicole Stempak is managing editor of EHS Today and conference content manager of the Safety Leadership Conference.

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