How Fire Burns
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Basics on the topic How Fire Burns
How fire burns
Today Uma is sitting by the campfire and enjoying marshmallows. As she does, so the question arises as to how fire actually burns.
In this video, we take a closer look and learn about the combustion triangle. The combustion triangle shows you exactly the three conditions it takes for a fire to start. These are oxygen, combustible materials and a certain ignition temperature. An experiment will show you what happens if one of the elements is missing.
You will also learn the difference between flammable and non-flammable substances.
After watching the video, you will no longer have to wonder how a fire can start.
Transcript How Fire Burns
What is better than sitting by the campfire roasting marshmallows? The fire crackles and lights up so beautifully! Have you ever wondered how fire burns? Let's take a closer look at how that happens. Here, we have two lit candles and we will place a glass over each. What do you observe about the glasses? The glass on the right is bigger. What do you predict will happen to the flames? The flames will go out. Which will go out first? The candle on the left because it is under a smaller glass. Let's see why this happens. We'll light the candles again and take a closer look. Under the glass is not only the candle but something else that we cannot see. What can that be? AIir! And in the air is oxygen! Because the glass is smaller, there is less oxygen than under the big glass. Due to the closed glass, no new oxygen can enter. Therefore, the flame in the small glass with less oxygen will go out before the flame in the larger glass with more oxygen. When the oxygen under the glasses is completely used up, their fires will go out. Now we know one important condition for combustion, or fire to burn: oxygen! But, it takes even more. Combustion also needs flammable materials. Here are some different types of materials. Wood, stones, petrol, newspaper, clothing and a saucepan. Which items do you think are flammable? If you would like additional thinking time, click on the pause button. Wood, just like Uma's campfire, is flammable. Newspapers are also flammable because they are made from wood, too. The t-shirt, made from cotton, is also flammable. And what about petrol? Petrol is very flammable! Its fire spreads very quickly! Can the stone and the saucepan catch fire? No, a stone is a non-flammable material and a saucepan is made of steel. Metals such as copper, iron, or steel can not burn. There are other, non-flammable substances used to extinguish fires like sand and water. But not every fire can be put out with water! An example is an oil fire in a frying pan! Putting water on hot oil will cause the fire to spread! This type of fire would need to be put out with salt. Now we need a third ingredient for combustion to happen. In order for the flammable material to ignite, or catch fire, it needs to reach a certain ignition temperature. To show this, we'll light the candle again with a match. The candle wick gets hot and heats the wax. When a certain ignition temperature is reached, the wick ignites and the candle burns. For fire to burn, it needs these three conditions. Together, they form this triangle. This is called a combustion triangle. If you take one of the three conditions away, then the fire goes out. This knowledge helps the fire and rescue service when putting out fires. Remember, fire can be dangerous, but also useful! Especially, to roast delicious marshmallows!
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How Fire Burns exercise
What are the three conditions for a fire to start?Hints
In this experiment, the candle goes out because no more oxygen can get to the flame.
Forest fires are more likely to happen in summer because the temperature is higher.
What does it take for the flammable material to catch fire?Solution
It takes oxygen, flammable materials, and a certain ignition temperature for a fire to start.
What happens if one of the three conditions needed for a fire is taken away?Hints
The combustion triangle shows us the three conditions that are needed for a fire to start.
Without flammable materials, there is nothing for the fire to burn.
In this experiment with the candles, when the oxygen in the glass covering the candle was used up, the fire went out.Solution
Oxygen, flammable materials, and a certain ignition temperature are the conditions for starting and sustaining a fire.
If we remove one of the conditions, the fire will go out.
What are the flammable and non-flammable materials?Hints
Think about those items that burn easily and those that do not catch fire.
Flammable materials, like cooking oil and plastic, burn easily.
Non-flammable materials, like glass and steel, do not catch fire.Solution
Wood, cotton, plastic, petrol, cooking oil and hand sanitiser are some examples of flammable materials.
Rocks, glass, copper and water are examples of non-flammable materials.
How does a fire use oxygen?Hints
Fires need oxygen to burn. When the oxygen runs out, the flame dies.
The larger glass has more oxygen inside for the flame to use.Solution
- The larger glass has more oxygen to feed the flame.
- The smaller glass has less oxygen to feed the flame.
- The smaller the glass, the shorter the flame will burn.
- The larger the glass, the longer the flame will burn.
What is true about fire?Hints
These are the necessary conditions needed for a fire.
Rocks are an example of a non-flammable material.
There are 2 correct answers.Solution
- The fire and rescue service should be called if there is a fire. Correct ✅
- Water or sand can help extinguish the flame. Correct ✅
- There are 4 necessary conditions to start a fire. Incorrect ❌ There are 3 conditions needed for a fire to start: oxygen, ignition temperature and flammable materials.
- Rocks, glass and water are flammable materials. Incorrect ❌ These materials are non flammable.
What have you learnt about fires?Hints
Combustion needs ignition temperature, oxygen and flammable material to create a flame.
What can be used to extinguish, or put out, one of the necessary components of combustion?Solution
- The fire and rescue service should be called if there is ever a fire.
- To put out the flame, firefighters can control the spread of the fire by taking away one of the three components that a fire needs to burn.
- The firefighters can lower the ignition temperature of a flame by using water or sand.
- The water or sand that is used to lower the ignition temperature will also remove the oxygen from the flame.
- With the oxygen removed and ignition temperature lowered, the flammable materials will not burn.
- When we remove any of the three components of fire, the flame will be extinguished.