HEPA filters are a type of air filter that can theoretically remove at least 99.97% of dust, pollen, mold, bacteria, and any particles in the air with a size of 0.3 microns (µm). If someone in your family suffers from a respiratory problem, such as allergies or asthma, then a HEPA filter could be the solution. HEPA filters are great for removing larger particles, such as pet dander, pollen, and dust mites. Unfortunately, mold, VOCs, viruses, bacteria, and small particles smaller than 0.3 microns cannot be safely removed from the air with a HEPA-based air purifier.HEPA filters have been designed to comply with strict U.
S. standards. Instead of functioning as a screen, they remove particles from the air by forcing them through a layered pattern of fiberglass mesh. This allows the filter to trap allergen particles of various sizes and remove them from the indoor air.
In an attempt to extend the useful life of a HEPA filter, a pre-filter can be included in the configuration that helps remove larger particles, leaving finer sized particles to be trapped by the HEPA filter. In theory, a HEPA filter is literally any filter that can capture at least 99.97% of very small particles of 0.3 microns in size. Common standards require that a HEPA air filter be removed from air passing through at least 99.95% (ISO, European Standard) or 99.97% (ASME, U. S.). This is beneficial for people with asthma and allergies, because the HEPA filter traps fine particles (such as pollen and feces from house dust mites) that it triggers allergy and asthma symptoms. At the microscopic level, there are 4 mechanisms for how HEPA filters manage to capture these tiny particles so well: interception, diffusion, inertial impaction and sieving.
Vacuums simply labeled HEPA may have a HEPA filter, but not all air necessarily passes through it. Many filters sold as HEPA can capture only 85 to 90 percent of all particles, and that percentage can decrease even further for particles of a micron or smaller. In conclusion, while HEPA air filters are great for removing larger particles such as pet dander and dust mites from the air, they are not effective at removing mold, VOCs, viruses or bacteria due to their size being too small for the filter to capture. It is important to note that while HEPA-based products were marketed for a long time with the intention of protecting against viruses, this is not their intended purpose.