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, for example, for clean room technology or applications in the nuclear 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. The scan method which is described in detail regarding procedure, apparatus and test conditions in the body of this standard is valid for the complete range of group H and U filters and is considered to be the reference test method for leak determination. The "Oil Thread Leak Test" according to Annex A and the "0.3 - 0.5 µm Particle Efficiency Leak Test" according to Annex E may be used alternatively but for defined classes of group H filters only.