What state must a fuel be in for combustion to occur?

For combustion to occur, the fuel must be in a state that allows it to react with an oxidizer (typically oxygen in the air) and produce heat and light. Fuels can exist in three different physical states: solid, liquid, or vapor/gas. Each state can participate in combustion under the right conditions.

Solids, such as wood or coal, can burn when they reach a sufficient temperature and emit flammable vapors. Liquids, like gasoline or oil, must first vaporize to form a combustible gas mixture with air. Gases, which include vapors from liquids and gaseous fuels like natural gas, readily mix with air and ignite when they encounter an ignition source.

This understanding emphasizes that all three states—solid, liquid, and vapor—are capable of sustaining combustion, highlighting the flexibility of fuel types in fire dynamics. This comprehensive approach is essential for firefighters in terms of fire prevention, control, and understanding material behavior during fires.