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What are HEPA filters?
HEPA filters, also known as absolute filters, are filters with an extremely high separation efficiency. These filters are capable of removing minuscule particles from the airflow. HEPA filters are used in hospitals and various industrial sectors where sterile air is a requirement. These include food processing companies and semiconductor manufacturers.
The essence of HEPA filters
The acronym HEPA stands for High Efficiency Particulate Air, indicating that these filters are particularly efficient in capturing microscopic particles. They are capable of trapping particles ranging from 0.1 to 0.2 microns and larger, including dust, pollen, mold spores, and even certain viruses. These filters can be used in various ways and are suitable for different applications. HEPA filters are especially used in environments where hygiene is crucial, such as hospitals and cleanrooms.
Operation of HEPA filters
The operation of HEPA filters is based on a combination of the mechanical and electrostatic properties of the filter media. The filter fibers, often made of glass fiber or synthetic materials, form a tight network. As air passes through the filter, particles are "captured" by the fibers. Small particles are captured through diffusion, while larger particles are mechanically blocked.
How are HEPA filters tested?
Absolute filters undergo various tests in accordance with the European EN1822 standard: 2019. After these tests, the filters receive a classification such as EPA, HEPA, or ULPA. Within these classifications, they are further subdivided with specific numbers such as E12, H13, or U16.
During the test with the test aerosol, measurements are taken. Given the variable performance of the filter at different measuring points on the filter surface, the minimum result is taken as a reference. The smallest particle that is allowed to pass through is known as MPPS. This stands for 'Most Penetrating Particle Size'. Smaller and larger particles than the MPPS are better captured than the MPPS.
What is the difference between EPA, HEPA, and ULPA filters?
EPA, HEPA, and ULPA filters all fall under the general term of absolute filters. However, there are significant differences. The main distinction lies in their efficiency in capturing MPPS. Absolute filters focus on the smallest particles, but the efficiency varies between 85% and 99.999995% for MPPS.
- EPA filters, which stands for 'Efficiency Particulate Air', have an efficiency of 85% to 99.5%.
- HEPA filters, which stands for 'High Efficiency Particulate Air', have an efficiency of 99.95% to 99.995%, allowing them to capture even more particles than EPA filters.
- ULPA filters, which stands for 'Ultra Low Particulate Air', go beyond HEPA filters with an efficiency of 99.99995% to 99.999995%.
| Filter class | Integral value Efficiency (%) | Penetration (%) | Local value Efficiency (%) | Penetration (%) |
| E10 | ≥85 | ≤15 | * | * |
| E11 | ≥95 | ≤5 | * | * |
| E12 | ≥99.5 | ≤0.5 | * | * |
| H13 | ≥99.95 | ≤0.05 | ≥99.75 | ≤0.25 |
| H14 | ≥99.995 | ≤0.005 | ≥99.975 | ≤0.025 |
| U15 | ≥99.9995 | ≤0.0005 | ≥99.9975 | ≤0.0025 |
| U16 | ≥99.99995 | ≤0.00005 | ≥99.99975 | ≤0.00025 |
| U17 | ≥99.999995 | ≤0.000005 | ≥99.9999 | ≤0.0001 |
Where are HEPA filters used?
HEPA filters are used in environments where air quality requirements are extremely high. The application often determines which filter class is needed and how the filter is installed.
Cleanrooms and the pharmaceutical industry In cleanrooms and in the production of medicines, the air must be free of dust particles, bacteria and other contaminants that could affect the production process or the final product. HEPA filters are often used here in combination with laminar airflow, creating a constant, low-particle environment. The required filter class is linked to the ISO cleanroom class of the space. Want to know more about filtration solutions for this sector? Read more about our solutions for the pharmaceutical industry
Hospitals and operating theatres In operating theatres and isolation rooms, HEPA filters prevent germs, viruses and bacteria from spreading through the air. This is essential for infection prevention, both to protect patients during surgery and for the isolation of contagious conditions.
Food industry In the production and packaging of food products, HEPA filters ensure that the air in production areas remains free of dust, mould spores and other particles that could compromise food safety. This aligns with the hygiene requirements arising from HACCP guidelines. Download our brochure on the food industry
Semiconductor industry In the production of chips and semiconductors, even the smallest dust particles can cause a production defect. HEPA and even ULPA filters provide a virtually particle-free environment here, which is essential for the precision of this type of production process.
Which filter class and which type of absolute filter best suits your application depends on the desired air quality and the required airflow rate. Our advisors are happy to think along with you.
When should you replace a HEPA filter?
A HEPA filter does not last indefinitely. As the filter captures more particles, its resistance increases. This directly affects the airflow and the energy consumption of the system.
- Signs that replacement is needed: the key indicator is the pressure drop (final resistance) across the filter. Once this reaches the recommended maximum value, the filter is saturated and needs to be replaced. A visible decrease in airflow or an increase in faults in the air handling system can also indicate a saturated filter.
- Why you cannot clean a HEPA filter: unlike coarser pre-filters, a HEPA filter cannot be cleaned or shaken out. The fine fibre structure responsible for the high separation efficiency is damaged during cleaning, causing an irreversible decline in filtration efficiency. Replacement is therefore the only option to guarantee the original performance.
- Testing and certification upon replacement: when replacing a HEPA filter in a critical environment, such as a cleanroom or operating theatre, a leak test (scan test) or DOP test is often carried out to check that the new filter and its installation comply with the required standard. Every absolute filter we supply is provided as standard with an individual test certificate in accordance with EN1822.
Free advice on HEPA filters?
Do you need more information or free advice on HEPA filters? Feel free to contact me and I will be happy to assist you in selecting the right absolute filter.
