| HEPA is an abbreviation for High Efficiency | | | | an UV light source to further destroy bacteria and |
| Particulate Arrestor. These filters are used | | | | viruses like the influenza virus too. The Clean Air |
| extensively in air cleaners and vacuum cleaners. | | | | Delivery Rate [CADR] varies from model to |
| HEPA was first developed and used by the USA | | | | model. |
| Atomic Energy Commission in 1940, to prevent | | | | These are different from other air cleaners. While |
| the spreading of airborne radioactive | | | | the latter work with UV lights and ionizers, HEPA |
| contaminants. It was used in the Manhattan | | | | filters physically remove the particles. The filter |
| Project during the development of the atomic | | | | doesn't act as a mere sieve for the particles. |
| bomb. It remained a classified gadget till the end | | | | Instead, purification is affected through three |
| of World War II, after which it was unclassified | | | | methods, diffusion, interception and impaction. |
| and released for commercial purposes. | | | | Interception occurs when a particle comes within |
| HEPA air cleaners are manufactured by a number | | | | the distance of one particle radius to a filter fiber |
| of different producers. One must be able to | | | | and gets stuck. It doesn't work if the distance is |
| distinguish between a true HEPA cleaner and a | | | | greater. Diffusion is best for smallest particles. |
| HEPA like cleaner. While the latter ones are | | | | Particles in the air constantly collide with each |
| cheaper, the former are more expensive but | | | | other. As a result they travel in a zigzag motion. |
| come with a guarantee. Some filters can also | | | | The smaller the particle, the more it zigzags and |
| require frequent change of parts and therefore | | | | the slower is its progress in the air current. |
| are not really cheap in the long run. | | | | Impaction works when a particle is so large that |
| HEPA air cleaners are theoretically reputed to | | | | it's unable to adjust to the sudden changes on |
| stop 99.97% of pollutants with particles smaller | | | | entering the filter. Due to its inertia, the particle |
| than 0.3 micrometers. This has been determined | | | | continues on its original path, hits, and gets |
| by the EN 1822 [European norm] test. The | | | | trapped by the filter fiber. Consequently, chances |
| efficiency of the cleaner also depends upon its | | | | of hitting the filter fiber are greater. It must be |
| location, that is, whether it is located after or | | | | kept in mind that these filters are effective only |
| before the motor. In case it is located before the | | | | for airborne particles and cannot be depended on, |
| motor, the carbon dust produced by it is also | | | | solely for a healthy environment. |
| caught. Some of the cleaners are equipped with | | | | |