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What is a HEPA Filter?

What is a HEPA Filter?

HEPA stands for high efficiency particulate air. A HEPA filter is a type of mechanical air filter; it works by forcing air through a fine mesh that traps harmful particles such as pollen, pet dander, dust mites, and tobacco smoke. You can find HEPA filters in most air purifiers and in almost every cleanroom.

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Why are HEPA Filters Important?

This type of air filter can theoretically remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns. Particles that are larger or smaller are trapped with even higher efficiency. Using the worst case particle size results in the worst case efficiency rating (i.e. 99.97% or better for all particle sizes).

This means that you can guarantee a clean and repeatable process, each and every time.

HEPA Filters for Cleanrooms

In almost every cleanroom, HEPA filters are a necessity. 

HEPA filters are often mounted in a HEPA fan filter unit. These units are self-contained with their own motor and are located in a cleanroom’s grid ceiling. 

HEPA filters can also be located in a terminal HEPA filter diffuser which sits in a ceiling. These are very similar to a conventional supply air diffuser, with the only difference being HEPA filter diffusers contain a HEPA median to filter the air.

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In certain designs, HEPA filters can be placed in a “bank” where a number of HEPA filters reside (based on ISO classification). Supply air then runs through these filters into the cleanroom space. 

For cleanrooms ISO class 8 or greater, HEPA filters are required. In more extreme situations, ULPA filters are required (ISO 4 or 5).


We hope this blog post gives you all the information needed to fully understand what HEPA filters are, and the role they play in your cleanroom design and construction.

For more information on cleanrooms, be sure to check out our blog.


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