| WHAT ARE
AIR CLEANERS?
Air cleaning devices are either central filtration systems put into the heating, ventilation, and air conditioning (HVAC) system of a home, or portable units with an attached fan to assist in reducing indoor air pollutants. Generally the central filtration systems require that the central heating or air conditioning fan be on in order for air cleaning to occur.
Mechanical filters draw air through a flat, pleated or high efficiency particulate air (HEPA) surface to trap particles. HEPA filters are the most efficient mechanical filters for removing small particles that can be breathed deep into the lungs. The highest efficiency air cleaners, widely available today, remove 0.3 micron (1 micron = 1 millionth of a meter) sized particles at a minimum of 99.97% efficiency.
Electronic air cleaners, in their simplest form, include negative ion generators that charge airborne particles so they become attracted to and settle on room surfaces. Activity within a room, however, may stir up and release the settled particles back into the air. More effective units called, electrostatic precipitators, electrically charge airborne particles and then trap them on oppositely charged metal plates. These plates must be cleaned regularly for proper performance.
Hybrid filters are made up of two or more of the above filters. An example is the "electret" filter which uses electrically charged flat or pleated fabric to attract airborne particles. These are efficient when clean, but as they fill with particles the efficiency decreases and they must be replaced. Cost and availability can be a factor to consider with these filters.
Gas phase filters are often attached to air cleaning devices to filter specific gases, vapors and odors. EFFICIENCY
The efficiency of an air cleaner is measured in terms of the particle size that the device can capture. In most cases, very small particles are the ones that penetrate deep into the lungs, causing health problems. Look for mechanical filters such as HEPA filters and electronic air cleaners that can effectively trap large and small particles. CLEAN AIR DELIVERY RATE
The overall effectiveness of an air-cleaning device depends on the efficiency of the unit and on the amount of air drawn through it. Although no industry-wide set of performance standards exists to help consumers compare units, the Association of Home Appliance Manufacturers has developed a standard for portable air cleaners called the "Clean Air Delivery Rate" (CADR). The CADR expresses the number of cubic feet of clean air a unit delivers each minute. OZONE
PRODUCTION
Some air cleaners (called ozone generators) use an electrical charge to generate ozone. Although ozone (also referred to as trivalent oxygen or saturated oxygen) is a necessary part of the upper atmosphere (10-30 miles above us), in the part of the atmosphere we breathe, ozone is a potent lung irritant. It can have damaging health effects, especially for persons with asthma and other lung diseases, children and the elderly. It is produced directly by ozone generators and indirectly by ion generators and some other electronic air cleaners. The FDA has set a limit of 0.05 parts per million of ozone in indoor air. Ask whether any electronic air cleaner you are considering buying has been tested for ozone production. The American Lung Association suggests that ozone generators not be used.
The limited available studies do not provide enough information to come to a conclusion about the health benefits of air cleaners. The American Lung Association recommends that proven source control strategies be employed as a primary means of reducing exposure to pollutants.
Based on the limited available data, if allergen sources are present in a residence, air cleaning alone has not been proven effective at reducing airborne allergen-containing particles to levels at which no adverse effects are anticipated. Cats, for example, generally shed allergen at a much greater rate than air cleaners can effect removal. Dust mites excrete allergens in fecal particles on the carpet or the bedding in the home. For individuals sensitive to dust mite allergen, the use of impermeable mattress coverings appears to be as effective as the use of an air-cleaning unit. Source control should always be the first choice for allergen control in residences.
If the choice is made to use an air cleaner, the reviewed evidence suggests choosing one that ensures high efficiency over an extended period of time (at least several months) and does not produce ozone levels above 0.05 parts per million, either intentionally or as a by-product of its design. If air cleaners are to be used, they should either contain charged or uncharged fibrous media, or they should conform to FDA regulations for medical devices.
The current reviewed data provides little reason to endorse the use of inexpensive tabletop, appliance-type air cleaners, regardless of the technology they employ. In general, high-efficiency particle collection requires larger filters or electronic air cleaners. For more information, visit the Environmental Protection Agency website. |
