http://www.louisville.edu/admin/dps/emergency/fire_inspections.htm

How do Fires kill?

Death caused by severe burns only cause approximately one-third of home-fire victims. The rest die from inhaling smoke and poisonous gases or from lack of oxygen.

* Suffocation: Fire consumes oxygen, which feeds a fire. Without oxygen humans and pets will suffocate. Normally, the air we breathe is 21 percent oxygen. During a fire, that level, decreases rapidly. When it drops below 17 percent, people breathing the air will experience decreased muscle control and decreased thinking ability. They may become uncoordinated, making escape more difficult. When the oxygen level drops below 11 percent, breathing stops. After four to six minutes without oxygen, brain death occurs.
* Products of Combustion: Fires produce smoke and poisonous gases. These are the leading causes of death in house fires. Most house fires occur at night while people are sleeping. A sleeping person may not wake up or collapse when they awaken.
* Heat: A fire can produce intense heat, which can exceed 1000 degrees. Breathing smoke and superheated air can cause lung damage. The body cannot regulate this amount of heat and can cause unconsciousness in minutes.