Air Scrubbers and Airborne Impurities

May 10, 2005
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The use of "air scrubbers" is relatively common in the mold and remediation industries today. However, although these machines have been around, in one form or another, for about 30 years, advances in air-scrubbing technology continue at a rapid pace, and cleaning professionals must stay abreast of new developments or find themselves falling behind their competitors.

An air scrubber, as the name implies, is designed to remove impurities from the air. We are most interested in removing bio-aerosols, the microorganisms, particles, gases, vapors, or fragments of biological origin. They are alive, or have been released from a living organism such as mold, bacteria, or fungi, and have become airborne. Bio-aerosols are everywhere in the environment but usually pose few problems as long as their quantities are kept within reasonable limits in most normal indoor situations.

However, if they grow beyond these reasonable limits or are found in large amounts in a medical or educational facility, some bio-aerosols can cause diseases, including pneumonia, asthma, rhinitis, and a variety of respiratory infections when inhaled for prolonged periods of time. Depending on humidity, light, temperature, and other factors, they can grow and multiply in HVAC systems, around doors and windows, and in cracks in walls, ceilings, and floors.

The chances of bio-aerosols becoming a problem increase considerably after a facility is subjected to excessive rain, flooding, or water damage, with forms of fungi and bacteria the most common microorganisms developing. The fungi and bacteria can produce spores, which become airborne and can include mycotoxins or endotoxins. When this happens, a high-powered air scrubber needs to be brought in to help remove the impurities from the indoor air and to protect the health of the facility and its occupants.

Designing an Air Scrubber
Air scrubbers come in an assortment of shapes and sizes. Some are made specifically for professional use-to tackle general and emergency cleanup operations-while other less professional equipment can be purchased at major hardware and home-improvement centers. These "home-use" machines are designed more to keep air cleaner - removing only larger impurities from the air - than to actually "scrub" it and remove the smallest of microorganisms.

The filter is probably the most important part of an air scrubber, according to Steve Williams, senior vice president of research and development with U.S. Products. The machine must be designed so that all air is drawn through the filter to remove impurities before moving out an exit portal. This is referred to as negative air movement, the "sucking" of air out of a room or facility.

Today, there are more than 200 U.S. manufacturers making a variety of different filters and filtering systems, and many may be used in air scrubbers. However, they can all be placed in four major categories. Flat filters contain a low-packing-density fibrous material that can be dry or coated with a viscous substance such as oil to increase particle adhesion. Carbon filters use activated carbon to absorb and trap airborne impurities and are particularly useful in eliminating odors. Pleated filters increase the filter media density by using smaller fibers. This increases the screening or straining mesh size of the filter to trap more and smaller particulates. However, any increase in filter density, with pleated or other types of filters, can significantly increase resistance to airflow and decrease airflow through the filter.

HEPA or high-efficiency particulate air filters are by far the most efficient filters now available. Developed during World War II to prevent the discharge of radioactive particles from nuclear reactor facility exhausts, HEPA filters are now used not only in air scrubbers but in a variety of industrial, medical, military, and clean-room applications, as well as in vacuum cleaners for professional and residential use.

HEPA, Bio-aerosols and Mold Spores
HEPA filters have a minimum particulate-removal efficiency rating of 99.97 percent for all airborne particulates of 0.3 microns or larger. This is more than adequate to remove most bio-aerosols, mold, and fungi spores, because those usually range in size from 2 to about 50 microns.

To get a better understanding of how small this is, the period at the end of this sentence equals about 615 microns; approximately 2,000 microns can fit on the tip of a pin; and there are more than 25,400 microns in one inch.

Because HEPA filters can trap particulates more than 100 times smaller than a mold or fungi spore, they are recommended for professional mold-remediation work. Williams also suggests using air scrubbers that have pre-filtering systems. "Using a pre-filtering system, allows the HEPA filter to stay cleaner longer so that it is more efficient, the unit draws less power, and filter does not need to be replaced as frequently," he said.

Working with Air Scrubbers
Air scrubbers are often used in the final stages of cleanup, disaster, or remediation operations. They are most effective once the source of the problem - the fungi, mold, or bacteria - has been completely removed.

With the increased concerns over indoor air quality, air scrubbers are being used to help remove airborne impurities and reduce the off-gassing associated with carpets and upholstery in newer or renovated buildings. Educational facilities use scrubbers to help remove allergens from the air that can trigger asthma and other respiratory problems. Air scrubbers are often used during and after building construction to remove potentially harmful airborne particulates. And they are being used to help clean up ventilation and HVAC systems to prevent Legionnaires' disease and other types of infections from occurring.

As it becomes clearer that the work of cleaning professionals is to maintain the health of a facility, employing equipment such as air scrubbers will become more commonplace. Although they are currently used extensively in remediation, new uses for air scrubbers in many settings can be expected in the future. And, for astute contractors looking for different ways to distinguish themselves from their competition and at the same time provide more offerings to their customers, incorporating air cleaning into their service arsenal can produce lucrative results.

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