Glowing gas, not glowing wood
What Actually Is a Flame?
A flame is not the wood burning — it is gas boiled out of the wood, glowing as it reacts with the air.
-
Step 1 of 5
Solid wood does not burn. Its gas does.
Heat the wood and it does not catch straight away — it first bakes, driving out flammable gases. It is those gases, mixing with air, that light.
-
Step 2 of 5
Fire needs three things at once.
Fuel, oxygen and enough heat. Take away any one and the flame stops, which is why a lid, a bucket of water and a firebreak all work.
-
Step 3 of 5
The flame keeps itself going.
The heat from burning gas bakes more gas out of the fuel below it. That is why fire spreads on its own once it is properly lit.
-
Step 4 of 5
The light comes from glowing soot.
A candle flame is full of tiny specks of unburnt carbon. They get so hot they glow yellow-white, exactly like the filament in an old bulb.
-
Step 5 of 5
Blowing a candle out removes the heat.
You blow the hot gas away from the wick. Without that heat the wick stops making new gas, and there is nothing left to burn.
A candle flame is roughly 1,400°C at its hottest edge, but only about 1,000°C in the dark cone at the middle, where the wax gas has not met air yet.
The short version
A flame is gas driven out of the fuel by heat, glowing as it reacts with oxygen — which is why removing heat, air or fuel all put it out.
Try it yourself
Blow out a candle and quickly hold a lit match in the trail of smoke, an inch above the wick. The flame runs down the smoke and relights it — proof the smoke was fuel.
Topics