Smoke inhalation is the number one cause of death related to fires. It occurs when you breathe in the products of combustion during a fire. Smoke inhalation damages the body by simple asphyxiation (lack of oxygen), chemical or thermal irritation, chemical asphyxiation, or a combination of these.
Combustion results from the rapid breakdown of a substance by heat (more commonly called burning). Smoke is a mixture of heated particles and gases. It is impossible to predict the exact composition of smoke produced by a fire. The products being burned, the temperature of the fire, and the amount of oxygen available to the fire all make a difference in the type of smoke produced.