This European Standard applies to efficient particulate air filters (EPA), high efficiency particulate air filters (HEPA) and ultra low penetration air filters (ULPA) 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 test aerosol, and allows a standardized classification of these filters in terms of their efficiency. This part of the EN 1822 series deals with measuring the efficiency of filter elements, specifying the conditions and procedures for carrying out tests, describing a specimen test apparatus and its components, and including the method for evaluating test results.