The fire triangle and the ignition point
Combustion is a reaction of a substance with oxygen that gives out heat and light. It needs three things, called the fire triangle: fuel, oxygen and heat. Take away any one of them and the fire stops. The ignition point is the lowest temperature at which a material starts to burn and goes on burning by itself. Flammability tells how easily a material catches fire at the temperature around it: petrol and alcohol are highly flammable, which is why their containers carry warning signs. Wet paper takes longer to burn than dry paper because the water soaks up heat, so the paper reaches its ignition point later. A match head holds a substance that gives oxygen, potassium chlorate, 2KClO₃ → 2KCl + 3O₂, and a fast-burning material. Rubbing the match on the box side makes heat by friction, and this heat starts the reaction. Careful: flammable is not the same as explosive. In a real fire, call the fire service and leave: never try to fight a fire yourself.
| Action | Side removed |
|---|---|
| lid on a pan | oxygen |
| shutting off the gas | fuel |
| cooling (water is not safe on every fire) | heat |
Fire-triangle sort, a talk with a grown-up and no flame. Write on cards: lid on a pan, fire blanket, shutting off the gas, cooling with water, removing dry leaves from a wall. Sort each under fuel, oxygen or heat (the side that is removed). Add one line to every card about whom to call. Do not light anything. Water is not the right tool for every fire, so the safest plan is to leave and call the fire service.