What is fire?

Fire is combustion: a fast reaction in which a fuel combines with an oxidizer, usually oxygen in air, releasing energy as heat and light. Three ingredients are needed, often drawn as the fire triangle: fuel, oxygen, and enough heat to start and sustain the reaction. When wood or gas is heated, it releases vapors that mix with oxygen and ignite. The reaction generates its own heat, which frees more fuel vapor and keeps the process going. A flame is the visible zone where these gases burn. Remove any side of the triangle and the fire stops, which is exactly how extinguishers work.

A flame's light comes from two sources. Tiny soot particles, heated white-hot, glow through incandescence, the same reason a stove element turns orange. Excited molecules and atoms also emit specific colors, giving flames their blue, yellow, or green tints depending on temperature and fuel. Flames point upward because hot combustion gases are less dense than the surrounding cool air, so buoyancy lifts them while fresh air is drawn in below. This convection feeds oxygen to the base. In weightlessness, without buoyancy, a candle flame becomes a dim, round, blue sphere, showing how much of fire's familiar shape depends on gravity.

Combustion still powers much of civilization. Burning coal, oil, and natural gas generates a large share of the world's electricity and moves most vehicles, though this releases carbon dioxide that drives climate change. Firefighters exploit combustion chemistry directly: water cools fuel below its ignition point, foam smothers oxygen, and dry chemicals interrupt the reaction. Wildfire scientists study how heat, wind, and dry fuel let flames spread, while controlled burns use fire deliberately to clear undergrowth and renew ecosystems. Many plants, such as certain pines, even depend on periodic fire to release their seeds, making fire a natural part of many landscapes rather than only a threat.

Myth: fire is a solid, liquid, or gas. Reality: it is a process, a chemical reaction, whose visible flame is mostly hot glowing gas and particles, not a state of matter. Myth: fire is always hotter the redder it looks. Reality: color tracks temperature, and blue flames are generally hotter than red or orange ones. Myth: fire needs pure oxygen. Reality: ordinary air, about 21 percent oxygen, is enough. Myth: smoke is the fire itself. Reality: smoke is unburned particles and gases carried up by heat, evidence of incomplete combustion. Myth: fire consumes matter into nothing. Reality: matter is converted into gases, ash, heat, and light, conserving mass.