Fire is what you see when something burns fast enough to glow. It needs three things at the same time: fuel (something to burn), oxygen (from the air), and heat (to get it going and keep it going). That's the fire triangle. Take away any one (smother the oxygen, soak up the heat, or run out of fuel) and the flame goes out at once. The flame itself is hot gas and tiny glowing bits of soot, lit up like a filament. In the simulator you can switch each leg off and watch the fire die.
Most people treat fire as a substance you can light and carry. In fact it is an event, a chemical reaction (rapid oxidation) happening fast enough to glow, which is why removing any one of fuel, oxygen or heat kills it instantly.
What's actually happening
We treat fire as an object (we light it, carry it, put it out) but it isn’t a substance at all. It’s an event: a chemical reaction happening fast enough to give off heat and light while it runs. Stop the reaction and there is nothing left called “fire”, only the warm, sooty leftovers. That’s why fire is so easy to kill compared with, say, a rock: it only exists while it’s being fed.
What it’s feeding on is the marriage of fuel and oxygen. Burning is oxidation gone quick: carbon and hydrogen in the fuel snap together with oxygen from the air to make carbon dioxide and water, and the leftover energy comes off as heat. That heat is the third partner — it’s what rips the next batch of fuel apart so the reaction keeps rolling. Fuel, oxygen, heat: the famous fire triangle. Remove any corner and the flame collapses. Blow it out (sweep away the hot gas), smother it with a lid or foam (cut the oxygen), douse it with water (steal the heat), or simply let it run out of fuel — every method is just an attack on one leg of the triangle.
The flame you see is the reaction made visible. Down low it can burn blue, where oxygen is plentiful and the gas itself glows. Higher up, where soot particles form and get white-hot before they finish burning, you get the familiar orange-yellow — that’s incandescence, the same glow as a light-bulb filament, just floating. Colour is a thermometer: a candle’s tip is hotter than its base, and a gas hob’s blue cone is hotter than any wood fire. Starve a flame of oxygen and it makes more soot, smokes, and may release carbon monoxide — the same reaction, run badly.
Fire is a reaction caught in the act, and its colour is a thermometer — blue is hotter than the yellow tip of a candle, because the glow is white-hot soot.
- 1Light a short candle (an adult nearby). It has all three: wax fuel, air, and its own heat.
- 2Lower a glass jar over it and watch: as the trapped oxygen runs out, the flame shrinks and dies — you removed one leg without touching the wax or the heat.
- 3Lift the jar, relight, and this time just blow steadily: you swept the hot gas away faster than it could reheat the wax. Two different legs, same dead flame.
Common questions
Each attacks one leg of the fire triangle: blowing it out sweeps away the hot gas, a lid or foam cuts the oxygen, water steals the heat, and it can simply run out of fuel.
Colour is a thermometer. Low down, plentiful oxygen makes the gas glow blue; higher up, soot particles get white-hot and glow orange-yellow. A blue gas flame is hotter than a candle's yellow tip.
With no gravity there is no "up" for hot gas to rise into, so a candle burns as a dim, near-spherical blue ball fed only by slow oxygen drift.