HEPAfilter

HEPAfilter, commonly known as a high‑efficiency particulate air filter, is a type of mechanical filtration device designed to capture at least 99.97 % of airborne particles that are 0.3 micrometres in diameter. The standard originates from the United States Department of Energy and the Institute of Environmental Sciences, and it is widely used in settings that require controlled air quality, including medical facilities, cleanrooms, laboratories, and residential air‑purifying devices.

Construction typically involves a dense mat of randomly arranged fibers, often made from glass, synthetic polymers, or a combination of both. Air passes through the filter media, and particles are removed by several mechanisms: interception, where particles follow air streamlines and come within one particle radius of a fiber; impaction, in which larger particles cannot navigate the airflow around fibers and collide with them; diffusion, which dominates for very small particles that move erratically due to Brownian motion; and electrostatic attraction in some filter designs.

HEPA filters are rated by efficiency at the most penetrating particle size (MPPS), approximately 0.3 µm, because particles of this size are the hardest to capture. Higher efficiency variants, such as ULPA (ultra‑low penetration air) filters, achieve 99.999 % removal at the same size. The performance of a HEPAfilter degrades over time as particles accumulate, leading to increased pressure drop and reduced airflow; regular inspection and replacement are essential for maintaining rated efficiency.

Applications extend beyond air purification to water treatment, vacuum cleaners, and industrial processes where particulate control is critical. Regulatory standards, such as ISO 29463 and EN 1822, define test methods and classification criteria for HEPA and ULPA filters, ensuring consistency across manufacturers and devices.