High Efficiency Particulate Air Filters and purifiers are used to ensure that particulate contents that form air pollution are filtered out. HEPA filters are used to filter out items such as dust, pollen, mold, bacteria gases and odors. They are commonly found in: hospitals, clean rooms, very high contamination-free electronic and health equipment assembly rooms, medication labs, places using hazardous materials, testing labs and dental labs. HEPA filters are also used against air pollution and cigarette smoke and they help people who are suffering from asthma and air borne allergies, nuclear plants, homes, schools, etc.
The most popular type of filters used for air purifiers are HEPA filters as manufacturers must meet rigid government requirements for these filters. HEPA filter requirements state that the filter must be able to filter out approximately 99.97 percent of air pollutants of down to 0.3 micrometers in size. The 99.97% specification is for particles that are exactly 0.3 micrometers in size as that is what is known as the most penetrating particle size. Any particles that are smaller or larger than 0.3 micrometers are theoretically filtered out with even higher efficiency. Therefore 0.3 micrometers is the worst case particle size and 99.97 percent is the worst case efficiency the filter should operate at.
HEPA filters are made up of a mat of fibers. The air space between the fibers is much greater than 0.3 micrometers. The general theory that a HEPA filter acts like a sieve where particles smaller than the hole size get through it is incorrect. In a HEPA filter, particles are trapped or stuck to the fibers by one of three mechanisms; diffusion, interception or impaction.
The original HEPA filter was designed in the 1940s for to help stop airborne radioactive contaminants from spreading. The original name became a registered trademark and soon became a generic term for highly efficient filters. Today, a HEPA filter generally refers to any high efficient air filter that can meet the efficiency standards of a HEPA filter.
HEPA filters are classified by: the number of fan speeds available, air delivery capacity in cubic feet per minute, maximum coverage area, efficiency of the system (should be greater than 99 %), energy and power consumption at different speeds, overall size, filter configuration (the number and types of filters that are arranged), filter life and control panel features. These devices may also be supplied with remote controls.