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Difference between EPA, HEPA, and ULPA filters

Absolute filters are also known as EPA, HEPA, and ULPA filters, but what exactly is the difference?

Absolute filters are used in spaces that need to meet extremely high air quality requirements. Some examples of such applications are: operating rooms, cleanrooms, and laboratories.

Higher quality requirements also mean a different air filter standard: absolute filters must meet the EN1822 standard in which ordinary air filters are tested through the ISO16890 standard. In addition, absolute filters are assigned a filter class, ranging from E10 to U16. The different filter classes are: E10, E11, E12, H13, H14, U15, and U16.

The letter of these filter classes refers to EPA (E), HEPA (H), and ULPA (U). The difference between these three types is in the efficiency of the filter.

A higher filter class is not always better. It depends on the application.

What are EPA, HEPA, and ULPA filters?

The difference between EPA, HEPA, and ULPA filters lies in their efficiency. Absolute filters filter the smaller dust particles, but there can be a difference of 85% to 99,99995% in efficiency.

EPA filters
EPA means ‘Efficiency Particulate Air’. The EPA filters have an efficiency of 85% to 99,5%. An EPA filter is capable of capturing very few dust particles from the air and, for example, can protect against infections.

HEPA filters
HEPA means ‘High Efficiency Particulate Air’. In comparison with EPA filters, HEPA filters can capture even smaller dust particles. HEPA filters have an efficiency of 99,995% on dust particles that are 0,3 microns or bigger.

ULPA filters
ULPA means ‘Ultra Low Particulate Air’. In comparison with HEPA filters, ULPA filters can capture even more smaller dust particles. The ULPA filters can capture 99,99995% of the dust particles that are 0,12 microns or bigger. The ULPA filters are, for example, used in cleanrooms.

The testing of absolute filters

Based on the European EN1822 standard, the absolute filters are tested in various ways. Among other things, particle measurement technology and a leakage test are used. Next, the filters receive an EPA, HEPA, or ULPA classification and within this classification, the filters are subdivided even further with a number. For example, E12, H13, or U16.

Testing the filter medium

To determine the efficiency of the filter, the filter medium gets tested first by using a particle counter. A part of the filter is placed in the so-called test filter holder. Next, the installation will blow a set test airflow through the filter at a pre-set pace. Testaërosol is added to this airflow.

The machine will blow air with the testaërosol through the filter for some time, so measurements can be made. Because the filter does not constantly perform in every area, the result will not be a straight line. Hence, it is based on the minimum result. That is also known as MPPS, which stands for ‘Most Penetrating Particle Size’. This means that most dust particles penetrate through the filter in that specific place. Because an absolute filter does not exist of only one layer, not too much can be concluded from this test. However, this is a basis for other tests.

Leak test of the filter
The leakage test is for absolute filters used to identify the reliability of the filter. The filter is entirely placed with the frame in the filter holder and then the installation is going to blow testaërosol through the filter. For this test, the minimum particle size is used (MPPS).

A computer analyses the complete filter during the test. A probe is placed in the airflow, and the computer registers the coordinates and measures the speed. In this way, leaks can be discovered. Because the leaks are mostly discovered on the edges of the filter, for example, at the border of the frame and the medium or seals, extra attention is paid to that. If the test shows that certain aspects allow a lot of dust particles to pass through, those aspects will be double-checked. If the filter meets the set requirements, the filter is seen as leak-proof.

The difference between EPA, HEPA, and ULPA filters

In short, listed in order the difference in the capturing of dust particles:

  • ULPA filters capture more and smaller dust particles than EPA and HEPA filters.
  • In terms of efficiency, the HEPA filters are between the EPA and ULPA filters.
  • The EPA filters are the least efficient compared to the HEPA and ULPA filters.

That does not mean that the ULPA filters are better in every situation. The starting point when choosing is the application. A cleanroom has different requirements than an industrial application. When a wrong filter is used, the filter can saturate much faster.

Absolute filters work most efficiently if the most suitable filter is considered specifically for each application.

Written by Stefan
Product Specialist at TOPS Luchtfilters

Want to know more about EPA, HEPA, and ULPA filters? Check out our product range of absolute filters or contact us.