Particulate matter is the name given to solids or liquids that are distributed in a gas. The hazard with airborne particulates is that a person may breathe in the chemical that, may have ill effects on an individual's health. The diagram below shows the parts of the respiratory system. It can divided in two systems - the upper airway passages and the lower airway passages.
Inhalation is the most important route of exposure in the workplace.
When particles are in the air, there is the chance that you will inhale them. How far the particle gets in the air passages of the respiratory system, and what it does when it is deposited, depends on the size, shape, and density of the particulate material. A particle is intercepted or deposited when it travels so close to a surface of the airway passages that an edge of the particle touches the surface. This method of deposition is most important for fibres such as asbestos. The fibre length determines where the particle will be intercepted.