1 Scope 1.1 This International Standard covers the evaluation of the performance of diffusive samplers of gases and vapours for use over sampling periods from 4 h to 12 h. Sampling periods of such duration are the most common in workplace sampling. Given a suitable exposure chamber, this International Standard can be straightforwardly extended to cover samplers for use over other sampling periods as well. The aim is to provide a concise set of experiments for classifying samplers primarily according to a single numerical value representing sampler accuracy. NOTE Accuracy estimates refer to conditions of sampler use which are normally expected in a workplace setting. These conditions may be characterized by the temperature, atmospheric pressure, humidity and ambient wind speed, none of which may be constant or accurately known. Furthermore, the accuracy accounts for difficulty in the estimation of time-weighted averages of concentrations which may not be constant in time. In addition to accuracy determination, a method is provided to test the samplers for compliance with the manufacturer's stated limits on capacity, possibly in the presence of interfering compounds. A method is given for classification of samplers according to their capability to detect situations in which sampler capacity may be exceeded. 1.2 This International Standard is an extension of previous research on diffusive samplers [1-17] as well as EN 838. Essential advantages are the estimation of sampler accuracy under actual conditions of use and the reduction in cost of sampler evaluation. NOTE Furthering the latter point, knowledge of similarity between analytes of interest can be used to expedite sampler evaluation. For example, interpolation of data characterizing the sampling of analytes at separated points of a homologous series of compounds is recommended. At present the procedure in [9] is suggested: Following evaluation of a sampler in use at a single homologous series member according to the present practice, higher molecular weight members would receive partial validations considering sampling rate, capacity, analytical recovery and interferences.