This document describes the methodology for measuring and characterizing the dustiness of bulk materials that contain or release respirable NOAA or other respirable particles, under standard and reproducible conditions and specifies for that purpose the small rotating drum method. This document specifies the selection of instruments and devices and the procedures for calculating and presenting the results. It also gives guidelines on the evaluation and reporting of the data. The methodology described in this document enables a) the measurement of the respirable dustiness mass fraction, b) the measurement of the number-based dustiness index of respirable particles in the particle size range from about 10 nm to about 1 µm, c) the measurement of the initial number-based emission rate and the time to reach 50 % of the total particle number released during testing, d) the measurement of the number-based particle size distribution of the released aerosol in the particle size range from about 10 nm to about 10 µm, e) the collection of released airborne particles in the respirable dustiness mass fraction for subsequent observations and analysis by analytical electron microscopy. NOTE 1 The particle size range described above is based on the equipment used during the pre-normative research . This document is applicable to the testing of a wide range of bulk materials including powders, granules or pellets containing or releasing respirable NOAA or other respirable particles in either unbound, bound uncoated and coated forms. NOTE 2 Currently no number-based classification scheme in terms of particle number and emission rate has been established for powder dustiness. Eventually, when a large number of measurement data has been obtained, the intention is to revise the document and to introduce such a classification scheme, if applicable. NOTE 3 The small rotating drum method has been applied to test the dustiness of a range of materials including nanoparticle oxides, nanoflakes, organoclays, clays, carbon black, graphite, carbon nanotubes, organic pigments, and pharmaceutical active ingredients. The method has thereby been proven to enable testing of a many different materials that can contain nanomaterials as the main component.