For a proper assessment of the toxic hazard, the size of the aerosols particles is important. Particles above 1 micrometer tend to deposit in the upper respiratory tract. Particles less than 1 micrometer in diameter enter the lung. Physiological Classifications of Toxic Materials Irritants are materials that cause inflammation of mucous membranes with which they come in contact. Inflammation of tissue results from concentration far below those needed to cause corrosion.
Irritants can also cause changes in the mechanics of respiration and lung function.
A primary irritant exerts no systemic toxic action because the products formed on the tissue of the respiratory tract are non-toxic or because the irritant action is far in excess of any systemic toxic action. A secondary irritants effect on mucous membranes is over-shadowed by a systemic effect resulting from absorption. Corrosives are chemicals which may cause visible destruction of or irreversible alterations in living tissue by chemical action at the site of contact. Asphyxiants have the ability to deprive tissue of oxygen. Simple asphyxiants are inert gases that displace oxygen.