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HEPA Filters – History and Function

HEPA, the most commonly known term in the world of air purifiers, actually stands for High Efficiency Particle Air. These are high-efficiency air filters that remove at least 99.97% of airborne particles measuring 0.3 micrometers in diameter and larger. These types of filters are best for filtering out allergens including pollen and smoke and commonly used in air purifiers.


HEPA filters originated in the 1940s when industry professionals wanted to inhibit the spread of radioactive contaminants during the Manhattan Project. It became commercialized in the 1950s and became widely used in various industries including computer manufacturing, pharmaceutical processing, healthcare facilities, and nuclear facilities. Although the term HEPA was once trademarked, today it is a term used to classify highly efficient air filters.


HEPA filters are composed of randomly arranged fibers that help trap tiny particles while still allowing airflow. Although the spaces between the fibers in HEPA filters commonly measure larger than 0.3 micrometers, these types of filters use other methods to help filter the air. The three types of HEPA filtration are as follows:
  • Impaction – the physical capture of larger particles that are unable to pass through the filter. Impaction increases as fiber density and air velocity increase.
  • Interception – airborne particles following the flow of air come close enough to a fiber and are attracted to it. In this instance they do not have to touch the fiber first in order to become attracted and adhere to the fiber.
  • Diffusion – the collision of tiny particles (usually measuring less than 0.1 micrometer) with gas molecules, impeding their path through the HEPA filter. This slow path increases the possibility of the particle being captured by either impaction or interception.
HEPA filters are used today in all types of industries. Nuclear facilities require high standards of air filtration and only HEPA filters are used. The same goes for hospitals that commonly pair high-grade HEPA filters with ultraviolet lights to help filter out and kill airborne viruses and bacteria. Even some household vacuums have HEPA filters to help reduce the amount of allergens circulated back into the air.