Key takeaways
- Under EN 1822-1, H13 filters are at least 99.95% efficient and H14 at least 99.995% at the most penetrating particle size.
- In practical terms, H14 lets through about ten times fewer particles than H13.
- A filter only performs if the air goes through it: seals, housings and leak testing matter.
- HEPA removes particles, not gases. Chemical vapours need a different technology, such as activated carbon.
How HEPA classes are defined
In Europe and many other regions, high-efficiency filters are classified under EN 1822-1. The standard groups filters into EPA (E10 to E12), HEPA (H13 and H14) and ULPA (U15 to U17). Each class has a minimum efficiency measured at the most penetrating particle size, often called MPPS.
- H13: at least 99.95% overall efficiency, with local efficiency of at least 99.75%.
- H14: at least 99.995% overall efficiency, with local efficiency of at least 99.975%.
- U15: at least 99.9995% overall efficiency.
The international standard ISO 29463 uses a different naming system. ISO 35 H is broadly comparable to H13, and ISO 45 H to H14.
Why the most penetrating particle size matters
Filters are not least efficient for the smallest particles. Very small particles are captured by diffusion and larger ones by interception and impaction. The weakest point sits in between, usually around 0.1 to 0.3 µm. Testing at that size gives a worst-case figure, so real-world efficiency for most particles is higher.
H13 or H14 in practice
The difference sounds small, but it is a factor of ten in what gets through. H13 passes up to 5 particles in 10,000 at MPPS; H14 passes up to 5 in 100,000. For protected environments for immunosuppressed patients, operating rooms for high-risk surgery and pharmacy preparation areas, H14 is the usual choice. For corridors, waiting areas and general wards, H13 can be appropriate, depending on the design.
The filter is only part of the system
Air that bypasses the filter is not filtered. Gaskets, frames, housings and the unit's own construction decide whether the rated efficiency is achieved. For fixed installations, leak testing after installation and at intervals confirms integrity. For mobile units, the manufacturer's construction and filter-change procedures matter just as much.
Airflow matters too. A high-grade filter in a unit that moves little air will clean a room slowly. Room volume, flow rate and the resulting air changes per hour decide how quickly particle levels fall.
What HEPA does not do
HEPA captures particles, including those carrying bacteria and fungal spores. It does not remove gases or volatile organic compounds. In IVF laboratories, pathology or reprocessing areas, chemical filtration with activated carbon is added. Some systems also combine filtration with technologies that inactivate captured microorganisms.
Related: HEPA units, PLASMAIR
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References
- EN 1822-1:2019. High efficiency air filters (EPA, HEPA and ULPA). Part 1: Classification, performance testing, marking.
- ISO 29463-1:2017. High efficiency filters and filter media for removing particles from air. Part 1: Classification, performance, testing and marking.
- Sehulster L, Chinn RYW. Guidelines for Environmental Infection Control in Health-Care Facilities. CDC and HICPAC, 2003 (updated 2019).
This article summarises published guidance and research for general information and is not medical or engineering advice. Device selection and use should follow the manufacturer's instructions, local regulations and your facility's policies.