This document provides the methodology for measuring 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 continuous drop 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 and, optionally, the inhalable dustiness mass fractions, b) the measurement of the number-based dustiness index of particles in the particle size range from about 10 nm to about 1 µm, c) the measurement of the number-based emission rate of particles in the particle size range from about 10 nm to about 1 µm, 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, and e) the collection of released airborne particles in the respirable dustiness mass fraction for subsequent observations and analysis by analytical electron microscopy. 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 1 – Currently no number-based classification scheme in terms of dustiness indices or emission rates have been established. Eventually, when a large number of measurement data has been obtained, the intention is to revise this document and to introduce such a classification scheme, if applicable. NOTE 2 – The methods specified in this document have not been evaluated for nanofibers and nanoplates.