To be classified as a HEPA filter, what minimum efficiency must it achieve?

To be classified as a HEPA filter, it must achieve a minimum efficiency of 99.97% on particles that are 0.3 microns in size. This specific measurement is critical because 0.3 microns is recognized as the most penetrating particle size, meaning that particles of this size represent the most difficult challenge for a filter to capture. HEPA filters are designed to trap fine particulate matter, including dust, pollen, mold spores, and some bacteria, which is why this standard is significant.

The rigorous standard ensures that HEPA filters provide a high level of air cleanliness and are effective for applications requiring stringent air quality, such as in hospitals, clean rooms, and laboratories. Therefore, achieving a minimum efficiency of 99.97% at the specified size demonstrates the filter's effectiveness in providing clean air and protecting health.