What kind of particles are HEPA filters specifically designed to capture?

HEPA filters are specifically designed to capture particles that are 0.3 microns in diameter and larger. This size is significant because 0.3 microns is considered the most penetrating particle size (MPPS) where conventional filtration methods are least effective. HEPA filters use a combination of mechanisms—interception, impaction, and diffusion—to trap airborne particles of this size and smaller. By achieving a minimum efficiency of 99.97% for these particles, HEPA filters provide a high level of air cleanliness, making them particularly effective for use in environments requiring stringent air quality standards, such as hospitals and laboratories.

Particles smaller than 0.3 microns are also captured to some degree, but the efficiency for these smaller particles is better understood through the overall performance of the filter across a broader range of particle sizes. Thus, the statement regarding particles 0.3 microns and larger accurately identifies the primary focus of HEPA filter design and performance.