Defines sampling conventions for particle size fractions for use in assessing possible health effects of airborne particles in the workplace and ambient environment. Defines conventions for the inhalable, thoracic and respirable fractions; extrathoracic and tracheobronchial conventions may be calculated from the defined conventions. The conventions should not be used in association with limit values defined in other terms, for example for limit values of fibres defined in terms of their length and diameter.