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HEPA Filters Overview

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Many of the more technologically advanced environmental inventions of the last century can be traced back to the Cold War. Though today’s uses of HEPA filters among your average American rarely get more exciting than an asthma attack, the invention of the HEPA filter is nothing less than “True Hollywood Story” material! HEPA filters were developed by the Atomic Energy Commission to filter radioactive particulate contaminants. In the 1940’s, a top secret project, the Manhattan Project (which gave us the atomic bomb) created an immediate need for HEPA filters. Once World War II was over, the technology that created the HEPA filter became declassified and available for uses other than military. Compared to the HEPA filters we have available today, the first ones in use were extremely large and bulky. Today’s residential and commercial HEPA filters are much more attractive, maneuverable and even more effective.

High-Efficiency Particulate Air filters (HEPA), formerly known as high-efficiency particulate arrestors, are a type of extended-surface media filter that was originally developed during World War II to prevent discharge of radioactive particles from nuclear reactor facility exhausts. Since their illustrious beginning, they have become of fundamental importance in industrial, medical, and military clean rooms and have grown as tremendously popular options for use as portable residential air cleaners.

HEPA devices have been traditionally defined as “an extended-surface dry-type filtration system having a minimum particle removal efficiency of 99.97% for all particles of 0.3 micron diameter with higher efficiency for both larger and smaller particles.” What a mouthful! In layman’s terms, this rating is determined by using a test that uses “challenge smoke” that consists of particles of 0.3 micron average diameter. A micron is one one-thousandth of a millimeter. It is hard to understand the comparative size of something that small. Consider the following example: a human hair is about 60-75 microns in diameter. Particles under 35 microns in size cannot be seen with the naked eye. Pollen is in the 10-100 micron size range with dust in the .5-5 micron range. That is really small! For many asthma sufferers, particles fewer than 5 microns are the most harmful and problematic because they have the greatest ability to penetrate deep into the lungs and wreak havoc.

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