page_title: HEPA
section_title: Mechanism
hierarchical_section_title: HEPA / Mechanism
caption_attribution_description: English: For mechanical filtration using a filter the filter's efficiency is dominated largely by the forces of diffusion, interception, and impaction. The lowest point on the curve represents the particle diameter for which the filter is least efficient.
context_page_description: High-efficiency particulate air, also known as high-efficiency particulate absorbing and high-efficiency particulate arrestance, is an efficiency standard of air filter.
  Filters meeting the HEPA standard must satisfy certain levels of efficiency. Common standards require that a HEPA air filter must remove—from the air that passes through—at least 99.95% or 99.97% of particles whose diameter is equal to 0.3 μm; with the filtration efficiency increasing for particle diameters both less than and greater than 0.3 μm. See the Mechanism and Specifications sections for more information.
  HEPA was commercialized in the 1950s, and the original term became a registered trademark and later a generic term for highly efficient filters. HEPA filters are used in applications that require contamination control, such as the manufacturing of disk drives, medical devices, semiconductors, nuclear, food and pharmaceutical products, as well as in hospitals, homes and vehicles.
context_section_description: HEPA filters are composed of a mat of randomly arranged fibres. The fibers are typically composed of fiberglass and possess diameters between 0.5 and 2.0 micrometers. Key factors affecting its functions are fiber diameter, filter thickness, and face velocity. The air space between HEPA filter fibers is typically much greater than 0.3 μm. Unlike sieves or membrane filters, where particles smaller than openings or pores can pass through, HEPA filters are designed to target a range of particle sizes. These particles are trapped (they stick to a fiber) through a combination of the following three mechanisms:
caption: Classic Collection Efficiency Curve with Filter Collection Mechanisms
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