This European Standard specifies a test rig method for the measurement of the separation efficiency by mass of air cleaning systems with unducted outlet, operating under defined conditions. The method shall apply to systems that clean air of aerosols (smoke, dust, fume, mist), vapour or gas. Measurement of the separation efficiency by mass of an air cleaning system for an intended use can serve for the: a) evaluation of the performance of an air cleaning system; b) evaluation of the improvement of the air cleaning system; c) comparison of air cleaning systems; d) ranking of air cleaning systems according to their separation efficiency by mass; e) determination of the state of the art of air cleaning systems of the same intended use with respect to their separation efficiency by mass.