Does Air Filtration Offer Solutions for Home Applications?
HAROLD D. FITCH
Occasionally, stepping back from leading-edge contamination control situations to see how technological advances in our field show up in everyday life can be interesting. We hear that very expensive scientific ventures like the space program contribute many advances to
everyday living and this alone makes these projects worthwhile. What about our own field? Do advances in contamination control technology contribute greatly to the quality of our everyday lives? What`s next?
Last year, I devoted a column to contamination control practices for safe food-handling in the kitchen. This was certainly an example of how contamination control practices are beneficial to all of us in everyday living.
This year, however, I thought I would look at how applications of air filtration affect us in our homes. Unfortunately, the benefits are not as clear cut as they were in the case above. The problem is that technological advances are more difficult and expensive to implement effectively in our homes. At first I thought the lack of inexpensive, easy-to-implement solutions might eliminate this as an appropriate topic. However, examining progress to date and some of the remaining problems might help develop improved solutions.
Cleaning can spread contamination
When I first got involved in contamination control, I learned that cleaning processes often evenly spread contamination everywhere as opposed to removing it. A good example of this is fingerprints on surfaces. Cleaning breaks the large fingerprint particles down into a much larger number of small particles that are then spread fairly uniformly over the whole surface being cleaned. The reason: fingerprints usually consist of clumps of skin particles held together by our body`s sebaceous oils, which the cleaning process does not remove. Instead, it breaks them up into numerous smaller particles which spread and stick tenaciously to the surface being cleaned.
In my experience, there were always two tools for cleaning a cleanroom–shoe cleaners and vacuum cleaners. However, instead of cleaning the room, they actually made it dirtier! Shoe cleaners caused major contamination because they utilized swirling brushes that stirred up and propelled the dirt removed from the shoes into the main airstream around the shoe cleaner. Eventually, this problem was solved by directing an air flow over the brushes to pick up the dirt particles in the airstream, and then exhausting it through HEPA filters, which removed the particles before the air re-entered the room.
Vacuum cleaners were just as bad for cleanrooms as dry skin flakes floating through the air. The vacuum cleaner picked up particles of all sizes from surfaces, but then blew millions of small particles into the cleanroom air via its exhaust stream. Finally, the problem was solved. Using special vacuum cleaners with HEPA filters installed in their exhaust stream, particles down to sub-micron size could be removed.
Vacuum cleaner particles
When I saw my wife vacuuming at home recently, I couldn`t help but think of that stream of fine particles the vacuum was spreading throughout the house. However, the HEPA-filter solution added to cleanroom vacuum cleaners about 20 years ago was only made available on home models in the 1990s.
Why did this take so long? Basically, it is a matter of cost and need. Cost is evident; need not so obvious. The standard vacuum was removing the majority of visible dirt accumulated in the cleaner bag. The fine dirt being blown back into the area was so small it was not visible to the naked eye. The only real evidence was a little odor associated with the fine dust, and that was certainly not very objectionable. People with allergies might be affected by the dust generated by the vacuum, but the vast majority of people were not. Today, there is still no good information about the size of the dust spread by your vacuum and whether it may have any long-term health effect.
Let`s look at the basic operation of vacuum cleaners and consider how technology can reduce the particles they give off. A vacuum cleaner uses an electrical fan to generate a fast-moving air stream which is blown out of the cleaner. This air flow generates the vacuum that draws air filled with dirt into the cleaner, where it passes through a filter bag. The bag traps much of the dirt before the air goes through the fan and out the exhaust. On some cleaners, the dirty air goes through the blower and then into the filter bag. This is known as a push vs. a pull cleaner. The exhaust air can contaminate the surrounding air by two methods. The first and major source of contamination is the dirt that passes through the filter bag and blown outside the cleaner. The second and lesser contamination source is simply the movement of the exhaust air itself which stirs up the existing dirt in the surrounding area.
Fixing the vacuum
The technological solutions to vacuum cleaner contamination are:
1. Remove the dirt going through the filter bag before the air is exhausted from the vacuum cleaner.
2. Route the exhaust air someplace else rather than the area being cleaned. This will reduce the dirt-stirring problem. The air may still have to be filtered, depending on where it is exhausted or what the contaminant is.
Finding a HEPA vacuum
Looking at a catalog offering several vacuum cleaners for sale for home use, prices range from about $50 to $250. The only HEPA-filtered model cost about $350–a premium of about $100 for the HEPA filter. Is this a good investment? I suspect so, but to make an informed buying decision, the consumer could use some factual information. A leading consumer test organization says that nearly two-thirds of its readers report two or more problems with their vacuum cleaners. They also report that test micro-filter cleaner bags have not shown much improvement in emissions over standard cleaner bags.
Looking in another catalog, an advertisement for an electrostatic furnace filter claims to remove 93 percent of pollen, dust, allergens, smoke and other pollutants vs. only 5 to 10 percent for standard furnace filters. However, it gives little technical data about the size of particles removed. In addition, this type of filter is only useful if the heating system in question is a hot air system.
Still another ad– for an air purifier — claims to remove particles 300 times smaller than the best HEPA filter (0.001 microns vs. 0.3 microns). You just plug it in and clean a 250 or 500 ft2 area, depending on the model size. The problem here is not that the air going through the filter won`t be that clean, but how it interacts with the room. What ensures that room air will pass through the purifier? What ensures that contaminated air will not be continuously drawn into the room, maybe even making the room dirtier instead of cleaner?
A major problem with all these devices is that we do not have the equipment and expertise in our homes to determine whether these units are really beneficial. It certainly appears that both the technology and the need for improved air in our indoor environments exist. Now someone has to develop reasonably priced, consumer friendly equipment and educate the consumer. n
Harold Fitch is president of Future Resource Development, a consulting firm in Burlington, VT, specializing in cleanroom education and problem-solving. He also conducts international training seminars for CleanRooms` shows and seminars.