Filtering Out the Facts

July 1, 1997
It seems that ideas for improving indoor air quality (IAQ) tend to float about in equal abundance to the dust particles schools try to eradicate. The

It seems that ideas for improving indoor air quality (IAQ) tend to float about in equal abundance to the dust particles schools try to eradicate. The dilemma comes when determining which ideas are sound, and which should be filtered out and discarded.

In a sense, released dust behaves much like an oil spill. In the ocean, an oil spill--driven by tides and currents--often disperses into and permeates the surrounding environment. Cleanup efforts often are ineffective, since the oil tends to fan out rapidly, preventing easy containment and removal.

Since released dust particles spread out rapidly into the ambient environment on currents of air, much of the damage already is done before remedial methods can have an impact. People inhale particles in the 10 micron and smaller range--the size often passing through vacuum cleaners and into the air. Equipment and building furnishings are covered with settling particulate, which later must be removed--to the extent possible--by cleaning personnel.

Plan of attack HVAC systems are largely ineffective at timely removal of released airborne dust because the volume of air processed is relatively low. By the time air is passed through the HVAC system, building occupants and furnishings already have been exposed to dust particles.

Also, though air-handling units can dilute airborne particulate by introducing varying amounts of outside air, this raises costs for heating and cooling without addressing the source of the problem.

While it probably is not necessary, or possible, to keep an educational facility's air as clean as a cleanroom's, establishing benchmarks allows the facilities manager to make and measure improvements. This process can be as scientific as counting airborne particles with an electronic device, or as simple as passing a white glove over a surface to check for settled dust, then saving the collected dust in a vial to compare with the next test.

Benchmarking also may be done empirically, by surveying cleaning workers and building occupants for their assessment of before and after dust levels on furnishings. By checking and recording dust levels consistently, you have the basis for determining how well the IAQ program is working.

Practical source-capture Source-capture, or prevention, is the best method for improving indoor air quality in stringent applications like cleanrooms and data centers. But how does it apply to less demanding facilities?

Source-capture in connection with vacuum cleaners is a vital strategy for keeping indoor air clean. This means ensuring good vacuum filtration. Without adequate filtration, vacuum cleaners often are a source of enormous airborne particulate. The finest particles suctioned from the floor and other areas are blown through cloth-bag filters into ambient air.

There are three important issues related to vacuum-cleaner filtration: *Filter efficiency. Since most respirable airborne dust falls into the 1 to 10 micron range, choose a multi-stage filter system that removes at least 96 to 99 percent of dust down to 1 micron. In contrast, older cloth-bag filters are only 30 percent efficient at removing 1 micron particles.

*Filter access. Choose a vacuum that permits simple filter maintenance. If filters are difficult to change or clean, operators will tend to allow them to clog, reducing suction and cleaning ability.

*Filter maintenance. Train operators to clean vacuum filters regularly--after every few hours of vacuuming or as needed to maintain optimum airflow and suction.

While newer high-efficiency vacuum filters are good at trapping fine dust particles at the source, efficiency comes at a price--more filter maintenance. This is because fine-mesh filters clog more rapidly, reducing airflow and suction, and require more attention to maintain peak efficiency.

Choose high-filtration vacuums with two design elements: ?Sealed body construction to prevent dust leaks. ?Easy-to-access filters that permit convenient cleaning and emptying. Punctured vacuum filters also allow dust to pass freely into the air. To prevent this, attach a magnetized strip to the floor tool, which will pick up paper clips, staples and other sharp metal objects that could otherwise enter the vacuum and penetrate vacuum filters.

Whichever systems you choose to improve indoor air quality, keep in mind that prevention rather than cure--capturing dust at its source rather than once it is airborne--is key to improved IAQ.

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