What is a HEPA filter?
Learn about protecting homes and industries from dangerous contaminants.
A HEPA (High Efficiency Particulate Air) filter is a fiberglass filter designed to protect individuals in a variety of industries from airborne particle contamination. HEPA filters provide 99.97-percent efficiency with airborne particles of 0.3 micrometers in diameter. Larger and smaller particles that are easier to trap are removed from the air at even higher efficiency rates. Standards for HEPA filter manufacturing, testing and performance are established and overseen by the U.S. Department of Energy.
History of the HEPA Filter
The HEPA filter was developed during World War II by the Atomic Energy Commission as protection from radioactive contamination for workers on the Manhattan Project (development of the atomic bomb). Originally classified, HEPA technology was de-classified after the war when a wealth of industrial applications became apparent.
Characteristics of the HEPA Filter
HEPA filters are made of fine-diameter fiberglass compressed into a fabric-paper sheet, which is then finely pleated to increase the particle-trapping surface area. Filters are subject to deterioration related to acid required in the paper-making process and to humidity-aging. DOE standards include strict testing and replacement requirements to maintain efficient functioning.
While industry standards include boron as a component of regular HEPA filter paper, within the last 10 years HEPA filters have also become available in a boron-oxide-free formula, created specifically to prevent deleterious effects of boron fumes on microchip manufacture.
Applications of the HEPA Filter
HEPA-filtered ventilation systems are used in hospitals worldwide to prevent contagion and control infection. Studies document a high level of effectiveness, especially in controlling tuberculosis. HEPA filtration is usually combined with ultraviolet germicidal irradiation to prevent contagion. In 2001 the U.S. Center for Disease Control interim recommendations to protect postal workers and first-responders from possible anthrax contamination included HEPA-filtered ventilation and the use of HEPA-filtered personal respirators. The State of Idaho recommends HEPA filtration for medical, public-health and other workers in danger of suspected hanta viruses.
Respirators and vacuum cleaners fitted with HEPA filters also figured in preventing inhalation of potentially-toxic mold spores during cleanup of damage caused by Hurricanes Katrina and Rita. HEPA filters remove both biological and chemical contaminants in the pharmaceuticals industry.
A large fraction of HEPA filtration focuses on relieving breathing problems experienced by asthmatic and allergic individuals exposed to indoor and outdoor air pollution. Home air cleaners address problems caused by dust, dust-mites, pet-dander and other possible allergy-triggering airborne particles. HEPA-equipped vacuum cleaners also address indoor pollution issues.
While HEPA filters exist for both air-conditioning and heating systems, the U.S. Department of Energy suggests the use of other kinds of filters because of the air-flow inhibitions caused by the density of HEPA filters. Protection devices to relieve outdoor-pollution symptoms range from passive face masks to portable air cleaners for cars.
HEPA-filtered ventilation systems protect workers in a number of non-medical industries. The needs of firefighters, the first stimulus to the development of respirators of several kinds, and other first responders such as police officers have produced a large market for HEPA-filtered personal and room-cleaning equipment. Coal miners experience similar problems with lung-damaging coal dust. HEPA filters produce clean air for workers in pesticide manufacturing and dispersal, along with workers exposed to lead dust through direct lead-abatement, construction and painting.