Under the term HEPA filter (from High Efficiency Particulate Air filter) refers to a particular high-efficiency filtration system for fluids or gases in general
Filter media: these are generally glass fibres or synthetic non-woven fibres (polyester or polypropylene) whose task is to block polluting solid particles (also known as particulates) present in the fluid to be treated. Solid particles may in fact be harmful to health or may affect the quality of the product or process to be obtained.
HEPA filters belong to the category of so-called 'absolute filters', to which ULPA filters also belong (Ultra Low Penetration Air).
The term 'absolute filter' is justified by the fact that HEPA and ULPA filters have a high filtration efficiency. In particular, HEPA filters have a filtration efficiency between 85% (H10) and 99.995% (H14), while ULPA filters have a filtration efficiency between 99.9995% (U15) and 99.999995% (U17).
They are classified according to their filtration efficiency of 0.3 µm particles, in accordance with UNI EN 1822. They are grouped into 5 classes (H10 to H14) with increasing performance characteristics.
They are tested by the dispersion method of a dioctjphthalate aerosol (DOP test): the calculated efficiency is > 99.999 % with particles with a diameter of 0.3 µm (penetration 0.001%).
Employment
HEPA filters have many possible uses, for example, they can be used in analysis laboratories, operating theatres in the electronics, chemical, food and pharmaceutical industries.
Recent years have also seen the integration of these systems in the home and work environment
as a filter element in vacuum cleaners, air conditioners, environmental purifiers and laminar flow hoods.
They can assume different positions along the filter path, even in series.
European regulations
The European standard for filter classification EN 1822-1:2009 refers to the classes:
- E10-E12 (EPA) high efficiency class also called "semi-absolute filters'
- H13-H14 (HEPA) very high efficiency class also called "absolute filters"
- U15-U17 (ULPA) very low penetration class.
Hepa filters in the market
Some products are named as 'HEPA-type', 'HEPA-like', 'HEPA-style' even '99% HEPA' without meeting the requirements of HEPA standards, and are also not tested by independent laboratories, even if of lower quality they may come close to filtering according to lower HEPA standards.
EPA / HEPA-Filter
The rating of the filter medium presents an index of lowest efficiency or highest penetration for a specific particle size. Class certification is based on the tests required by EN 1822 and are shown in the following tables:
| Class | Efficiency | Penetration |
| E10 | > 85% | ≤ 15 |
| E11 | > 95% | ≤ 5 |
| E12 | > 99.5% | ≤ 0,5 |
| H13 | > 99.95% | ≤ 0,05 |
| H14 | > 99.995% | ≤ 0,005 |
ULPA-Filter
| Class | Efficiency | Penetration |
| U15 | > 99.9995% | ≤ 0,0005 |
| U16 | > 99.99995% | ≤ 0,00005 |
| U17 | > 99.999995% | ≤ 0,000005 |
