This European Standard applies to efficient air filters (EPA), high efficiency air filters (HEPA) and ultra low penetration air filters (ULPA- 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 an artificial test aerosol, and allows a standardized classification of these filters in terms of their efficiency. Part 4 of this standard applies to the leak testing of filter elements.