HEPA

HEPA stands for High-Efficiency Particulate Air. It refers to a type of air filter engineered to remove a high fraction of small particles from the air circulating through a system. HEPA filters are typically made from pleated glass fiber media enclosed in a rigid frame, creating a dense barrier that traps particles as air passes through.

Filtration mechanisms include diffusion, interception, and impaction. Diffusion is especially effective for very small particles, while interception and impaction handle larger ones. These filters are designed to achieve high efficiency while maintaining an acceptable airflow resistance.

Standards and performance vary by region. In the United States, a widely cited benchmark requires capturing at least 99.97% of particles at a test size of 0.3 micrometers. In Europe, the EN 1822 standard classifies HEPA filters into grades such as H13 (at least 99.95%) and H14 (at least 99.995%) based on MPPS testing. Higher-grade filters, known as ULPA, offer even greater efficiencies for very small particles.

Common applications include cleanrooms, hospitals, laboratories, pharmaceutical manufacturing, nuclear facilities, and consumer devices such as air purifiers and vacuum cleaners. In many setups, HEPA filters are paired with prefilters and activated carbon to extend life and address odors or gases.

Limitations and considerations: HEPA filters do not remove gases or volatile organic compounds. They must be properly installed and sealed, and replaced when loading reduces effectiveness or airflow becomes restricted to prevent release of trapped particulates.

History: HEPA technology developed in the 1940s for nuclear and other high-purity applications and later spread to broader commercial and consumer uses.