Grade 6 (age 11-12)

grade 6 Combustion & Fire Extinguishing

Combustion is a substance burning and giving off light and heat, and it needs three things together: something to burn, oxygen and a temperature at or above the ignition point. So removing just one of the three puts a fire out, and spraying water to lower the temperature or covering a fire to shut out oxygen both use this idea to extinguish it. When a candle burns, carbon dioxide and water are produced; the carbon dioxide can be detected because it turns limewater cloudy. In the first picture, switch the conditions off one at a time to see when the fire goes out; in the second, compare the three ways of putting out a fire.

What does a fire need?

🔥 The three conditions for burning

①Combustion is a substance burning and giving off light and heat.

②Fuel: there must be something that can burn, such as wood, paper, a candle or gas.

③Oxygen: oxygen from the air has to keep reaching the fire.

④A temperature at or above the ignition point: the lowest temperature at which a substance catches fire is its ignition point, about 230 °C for paper and about 300 °C for wood.

⑤If even one of the three is missing, the fire will not start or will go out.

Three ways to put out a fire

🧯 How putting out a fire works

①Remove the fuel: turn off the gas valve on a stove, or cut down trees ahead of a forest fire so it cannot spread.

②Shut out oxygen: cover it with a lid or a wet blanket, or throw sand on it.

③Cool it down: spray water to bring it below the ignition point.

④Water makes oil fires and electrical fires more dangerous, so cover them or use the right kind of extinguisher.

⑤An extinguisher covers the fire with powder or foam, shutting out oxygen and cooling it too.

What burning produces

Fuel + oxygen → carbon dioxide + water + light and heat

When something containing carbon and hydrogen, like a candle or wood, burns, carbon dioxide and water are produced.

💡 Checking what burning produces

①Turn a cold glass upside down over a candle flame and the inside fogs up with droplets: water has been produced.

②After the candle burns, add limewater to the gas in the glass and shake it: it turns cloudy, so carbon dioxide has been produced.

③Burning without enough oxygen makes black soot and can also make harmful carbon monoxide.

④In a fire, cover your nose and mouth with a wet cloth and stay low as you escape.

Summary

Conditions for burning

Fuel + oxygen + temperature above the ignition point → combustion

All three must be present for a fire to burn.

How fires are put out

Remove one condition for burning → the fire goes out

Remove the fuel, shut out oxygen, cool it down.

🎯 Key points

①The three conditions for burning are fuel, oxygen and a temperature above the ignition point.

②Removing any one of them puts the fire out; this is how extinguishing works.

③Burning produces carbon dioxide and water.

④Carbon dioxide is detected with limewater, and water by droplets on a cold glass.

⑤In a fire, cover your nose and mouth with a wet cloth and stay low as you escape.

Examples and Unit Test

Example 1

A candle covered completely with a glass goes out after a short while. Which of the three conditions for burning disappeared?

Burning needs fuel, oxygen and a temperature above the ignition point, all together.

With the glass on top, no fresh air can get in, so once the oxygen inside is used up the candle cannot keep burning.

▸ Oxygen, because no more could get in

In the first picture, switching off only the oxygen makes the fire in the middle disappear.

Example 2

What substances are produced when a candle burns, and how can you detect the carbon dioxide?

A burning candle produces carbon dioxide and water.

Carbon dioxide can be detected because it turns limewater cloudy.

▸ Carbon dioxide and water / limewater turns cloudy.

Burning uses up oxygen and gives off carbon dioxide and water.

Unit-test style

Which statement about burning and putting out fires is correct?

①Burning does not need oxygen.

②Spraying water to lower the temperature can put out a fire.

③Putting out a fire means providing all three conditions for burning.

④A burning candle produces new oxygen.

⑤Things catch fire easily even below their ignition point.

▸ ② Spraying water to lower the temperature can put out a fire.

Lowering the temperature below the ignition point breaks one of the conditions, so the fire goes out.

Burning needs oxygen (①), putting out a fire removes a condition (③), burning produces carbon dioxide and water (④), and a fire needs a temperature above the ignition point (⑤).

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Last updated 2026-10-17