The lungs are the main route for dust entering the human body. Dust deposition in the pulmonary system varies considerably according to the granulometry of ultrafine dusts and their airborne behaviour. Normally, for coarser dusts encountered in work environments, the proportion of dusts deposited in the alveolar region increases as particle diameter decreases, reaching a maximum value of around 20% for 3-micrometre particles. This percentage then diminishes gradually. This situation has led hygienists and occupational health physicians to consider reflexively that the smaller the particle, the deeper it is deposited in the lungs. They should beware of this reflex.
