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

To be classified as a HEPA (High-Efficiency Particulate Air) filter, it must achieve a minimum efficiency of 99.97% on particles that are 0.3 microns in size. This specification is critical because the 0.3-micron particle size is considered the most penetrating particle size (MPPS) for HEPA filters. At this size, the filter's design effectively captures the maximum number of particles, ensuring high air quality and removal of airborne contaminants.

The requirement of 99.97% efficiency means that out of 10,000 particles at this size that enter the filter, only three would be allowed to pass through. This level of filtration is essential in various applications, including hospitals, clean rooms, and settings where air quality is paramount.

The other options fall short of the established criteria for HEPA filters, which is why they do not qualify. For example, an efficiency of 95% or lower on particles of larger sizes does not meet the stringent standard set for HEPA classification, underscoring the necessity of the 99.97% minimum efficiency for maintaining effective air filtration in sensitive environments.