How Fires Start: The Science of Combustion

Fires require three elements in the right combination: heat, fuel, and oxygen. Remove any one of these and the fire goes out. This is the foundation of every fire prevention and suppression strategy in existence.

Heat is the energy source that initiates and sustains combustion. Common heat sources include open flames, electrical current, friction, sparks, hot surfaces, and chemical reactions. The heat must be sufficient to raise the fuel to its ignition temperature—the point at which it begins to produce its own flammable vapors.

Fuel is any combustible material that can sustain the fire. In homes, fuel includes wood, paper, textiles, plastics, cooking oils, and flammable gases. The physical form of the fuel affects how quickly it ignites—gases and fine dusts ignite more rapidly than solid materials.

Oxygen in the air provides the oxidizing agent for combustion. Normal atmospheric air contains approximately 21 percent oxygen. Most fires require at least 16 percent oxygen concentration to sustain burning. This is why smothering a fire with a fire blanket or lid effectively extinguishes it.