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This document defines sampling conventions for airborne particle size fractions for use in assessing the health relevant exposure from inhalation of particles in the workplace. Conventions are defined for the inhalable, thoracic and respirable fractions. The sampling conventions only describe the inhalation of particles and their penetration in the respiratory tract as governed by inertia (impaction). Deposition in the respiratory tract by other mechanisms, e.g. diffusion, is not considered in this document. The sampling conventions defined in this document apply to both indoor and outdoor workplaces. The assumptions on which the sampling conventions are defined are given in Clause 6. The convention chosen for a specific application will depend on the region of the health effect of the component of interest in the airborne particles (see Clause 5). The conventions can be used with whatever metric is of interest, including particle count, length, surface area, volume or mass. The metric depends on the kind of particle analysis carried out on the sampled aerosol fraction. The health-related fraction concentrations defined in this document are often expressed in mass of the sampled particles per volume of sampled air in order to compare with mass-based occupational exposure limit values. The conventions are not applicable in association with limit values expressed in a different metric, e.g. for fibre limit values defined in terms of the length and diameter of airborne fibres and the ratio of the two (aspect ratio), unless a measurement procedure explicitly requires that a specific health related size fraction is to be sampled/collected [13]. The main purpose of this document is to provide agreement on the particle size fractions to sample and their definitions. Sampling is generally carried out using dedicated samplers, for which there is no need to measure the aerodynamic size distribution of the airborne particles to be sampled. Samplers including a separation into one or more relevant sampling conventions(s) are currently available. In general, no assumptions or pre-knowledge are needed on the number of modes, modal diameter(s) or width of the particle aerodynamic size distribution of the airborne particles to be sampled. Because there is a wide variation from one person to another in the probability of particle inhalation, deposition, reaction to deposition and clearance, this document is not applicable for determining the deposited dose taken up by an individual worker. The conventions are primarily intended for determining workers’ exposure to airborne particles by sampling the airborne particles. This document is not applicable to large particles emitted at high speed that are travelling under the momentum from their emission, instead of being carried by the air (airborne) and aspirated into humans and aerosol samplers by their suction (see Annex B).