The standard is applied to high and very high efficiency air filters with ultra-low penetration (EPA, HEPA and ULPA) used in the field of ventilation and air-conditioning, as well as in technological processes such as clean-room technology or the pharmaceutical industry. It establishes a procedure to determine efficiency based on a method that counts particles with a test liquid aerosol (or alternatively a solid one) and can classify these filters in a normalised way depending on their efficiency.
The following table shows the various classes for high efficiency filters in accordance with EN 1822:
The EN 1822 standard defines methods to:
A) assess the efficiency of the filtering medium. By using a particle contactor, the number and size of the particles trapped by the filter can be determined. After processing this data, the size of the particle, for which the efficiency of the medium is minimal, can be determined. This size is known as MPPS, which stands for most penetrating particle size.
B) check for leaks from the filtering element. This test is conducted with a probe that produces aerosol and can be moved along the whole surface of the filter in order to collect a series of data on the local efficiency, which will be then used to determine the overall efficiency. This also allows the leak rate on a specific area of the filter to be determined. The calculation of the overall efficiency is often defined as an integral value, while the leak rate is defined as a local value.
C) determination of the integral efficiency of the filtering element. First, one measures the pressure drop of the filter at an air volumetric flow rate corresponding to the rated flow rate. Then, with an aerosol generator the filters efficiency on the MPPS particles is determined. Based on this efficiency value, the class is determined in accordance with the table reported above.