The fire triangle

About this video

Watch a candle burn for an evening and it gets shorter. The wax doesn't vanish: burning is a chemical reaction. The wax is a fuel, and it reacts with oxygen, a gas that makes up about one-fifth of the air. The products are carbon dioxide and water vapour, two gases you can't see, so they float away into the room. The reaction also gives off a lot of heat and light, and the flame is the glowing, very hot gas where it is happening.

A fire needs a third thing before it will start: heat. A candle won't light by itself, even though wax and air are touching all the time. A match gives the first heat, and after that the flame makes enough heat to keep itself going. So a fire needs fuel, oxygen and heat. People draw this as the fire triangle, with one thing on each side.

Take away any one side and the fire goes out. When a candle's wax is used up, the flame dies. A jar over a candle, a lid on a pan or a fire blanket stops fresh air getting in. Water cools a campfire until it can't keep burning. Every way of putting out a fire takes away one side of the triangle.

Fire is only ever for an adult to light. This video goes with the lesson What Is Fire? in Chemistry Level 1 on Knaph.

Transcript

1. 0:00A candle gets shorter as it burns. Where does the wax go?
2. 0:07Burning is a chemical reaction. Wax and oxygen from the air turn into carbon dioxide and water vapour, two gases you can't see.
3. 0:16A fire needs three things. Fuel, oxygen, and heat to start it. That's the fire triangle.
4. 0:24Take one away and the fire goes out. The wax runs out, a jar keeps the air away, or water cools it down.
5. 0:36A flame isn't a thing. It's a reaction happening.