When it comes to air filtration, HEPA filters are the gold standard. This type of filter 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. By using a commercial air filtration system equipped with a HEPA filter, most dirt, dust, mold and bacteria are filtered out of the air and are trapped in the filter. CADR stands for “clean air supply rate” and simply means how much air flows through the filter.
However, it is not a reliable number. To produce the cleanest possible air, the HEPA filters and air purifiers in which they are used must be adapted to the space. There should be a tight and secure seal to help ensure that particles are properly filtered out of the air as they pass through the filter. HEPA-type filters are made of the same materials as true HEPA filters, but they only capture 99.84% or less of particles as small as 0.3 microns. We do not recommend washing HEPA filters, even if they are intended to be reused, as the washing process will likely cause minor damage to the filter that reduces its effectiveness over time. In the US, look for the terms “true HEPA” and “absolute HEPA”, which indicate that you do qualify.
Absolute HEPA is sometimes used to mean the same thing as True HEPA, although sometimes it seems to indicate an even better filtration power claim, up to 99.999 percent at 0.3 microns. In facilities such as hospitals and schools, including HEPA filters in their cleaning and maintenance program is an important way to protect the health of vulnerable occupants and avoid closures and absences. HEPA filters are pleated mechanical air filters that have a considerable thickness to capture particles. They are designed to effectively stop very fine particles, but they don't filter gases or odor molecules. When used with an activated carbon filter, smoke, odors and gases can also be removed and trapped. Critics have expressed concern about the effectiveness and repair status of air filtration systems, as they think that much of the air in an aircraft cabin is recirculated.
People suffering from dust or seasonal allergies can find relief by using purifiers with HEPA filters during times of the year when allergies worsen.