When the very highest level of Air Purity is required, we opt for HEPA & UPLA filters mainly for applications in Clean Rooms & Hospital Operating Theatres. EN 1822-2019 is the most accepted international test standard for the filter classification of HEPA and ULPA filters developed by the European Standardization institute. It mainly applies to filters used in the field of ventilation and air conditioning and for technical processes, e.g., for applications in clean room technology or pharmaceutical industry. It establishes a procedure for the determination of the efficiency on the basis of a particle counting method using a liquid (or alternatively a solid) test aerosol and allows a standardized classification of these filters in terms of their efficiency, both local and integral efficiency.
According to this standard, filter elements fall into one of the following Groups:
— EPA filters (Efficient Particulate Air filter);
— HEPA filters (High Efficiency Particulate Air filter);
— ULPA filters (Ultra Low Penetration Air filter).
The table shows the various classifications of EPA, HEPA & UPLA filters per EN 1822:2019
During the test procedure as a first step the Most Penetrating Particle Size (MPPS) is determined for a flat sheet filter media for a given media velocity. The filter is manufactured with specified media grade and amount of media to comply with the defined media velocity.To test the filter element, it is subjected to a constant airflow from an aerosol with an average particle size which corresponds to the hardest particle size to capture (MPPS). Using movable probes, local particle concentrations are measured on the downstream side, which give together with the particle concentrations measured on the upstream side the results for the local penetration and the local collection efficiencies, respectively. If the local penetration values stay within the limits set out in the standard for each individual filter class, the filter can be classified as leak-free. Similarly, the overall efficiency of the filter is also tested to meet the specified values set forth as per the standard. Leaks are specified as maximum allowable local penetration at MPPS and must not exceed 5 x the overall penetration.
As part of this process, pressure loss is also measured for each filter element.
If the test is successful, a test report will certify the filter’s leak-free status and also its integral particle collection efficiencies. The filter will then receive an individual identification number and test certificate.
Unlike HEPA / ULPA filters, EPA filters are not tested individually for local penetration. EPA filters are subject to a type test, in which collection efficiencies are determined as an average of certain random tests as part of the quality control.
(All above information & Data are derived from Book records of Filtration Standards & Other related standards, research papers and its related webpages)