HEPA filters are designed to remove particles as small as what size?

• A. 0.1 microns
• B. 0.2 microns
• C. 0.3 microns
• D. 0.4 microns

Answer: (C)

HEPA filters are designed to capture particles as small as 0.3 microns in diameter with a high efficiency of at least 99.97%. This capability is essential in sterile compounding environments, as it ensures that airborne contaminants, including bacteria and other particulates, are effectively filtered out, maintaining the sterility of the compounding area. The 0.3-micron size is particularly significant because it represents the most penetrating particle size (MPPS), meaning that particles of this size are the most difficult for filters to capture. Although HEPA filters are also effective at capturing larger and smaller particles, understanding that 0.3 microns is the benchmark for their performance helps emphasize their critical role in maintaining a sterile environment.