Inhalation risk and particle size in dust and mist.

Respiratory Absorption and Elimination The human respiratory system has long been known to filter the air passing through it. Lord Lister demonstrated that putrefactive organisms were not present in air passing out of the lungs and in 1869 Tyndall (1881) found that air expelled towards the end of a breath failed to produce scattered light near the focus of a light beam and caused the white track of the beam, due to atmospheric dust, to disappear. These early observations are incomplete: as a rule, when dusty air is inhaled, only a proportion of the dust is retained in the body while the rest is expelled. The particles which are left behind deposit in different regions of the breathing tract according to their size. The coarsest get trapped in the rnose in normal breathing,