| The military designed the first HEPA filter in the | | | | the charcoal matter in the filter. |
| 1940s for use in the Manhattan Project, when | | | | Some fans have a straight design whereby the |
| safety from free-floating nuclear material was a | | | | air is drawn in from the back and blown out |
| primary concern. Today, HEPA air purifiers are | | | | through the front. These units clean the air very |
| very widely used to remove dust, pollen, mold, | | | | quickly and are good for aiming at your bed or |
| bacteria, and other airborne particles. | | | | sitting area. |
| They are perhaps the most tried-and-true | | | | Other fans are unidirectional, pulling in air from all |
| method of air cleaning to date. The best part | | | | sides of the machine and blowing the filtered air |
| about HEPA air purifiers is that they emit no | | | | out in all directions. These are good for cleaning |
| byproducts or secondary pollutants such as ozone. | | | | the air in whole rooms. |
| The Department of Energy continues to be the | | | | Related to HEPA filters are ULPA filters. ULPA |
| sole certifying body for all HEPA filters. The DOE | | | | means Ultra High Efficiency Particulate Air. ULPA |
| has strict standards. All HEPA filters must be able | | | | filters are only used when there is a significant |
| to catch at least 95% of particles as small as 0.3 | | | | biohazard or equally harmful environment. You |
| micrometers. If you are shopping for HEPA air | | | | won’t need one at home; if you do, you |
| purifiers, beware of HEPA-type or | | | | shouldn’t be living there. |
| HEPA-like filters. They did not pass DOE | | | | Friedrich, Oreck, and Whirlpool are some of the |
| muster on their ability to filter air. | | | | leaders of the industry. Their HEPA air purifiers |
| HEPA Air purifiers work by drawing in air via a | | | | are known for their relative quietness, air-cleaning |
| fan. Large particles get trapped in the folds of the | | | | efficacy, and energy efficiency. |
| filter, while small particles and chemicals attach to | | | | |