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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 that else that we CAN NOT see. What can that be? AIR! And in the air is oxygen! Because the glass is smaller, there is LESS oxygen than is under the big glass. Due to the closed glass, no new oxygen can come in. 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... gasoline... newspaper... clothing... and a saucepan. Which items do you think are flammable? If you would like additional think 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 gasoline? Gasoline 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 clear fires like sand and water. But not every fire can be put out with water! An example is a grease fire in a frying pan! Putting water on hot grease 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 department when putting out fires. Remember...fire can be dangerous, but also useful! Especially, to roast delicious marshmallows!

How Fire Burns exercise

Would you like to apply the knowledge you’ve learned? You can review and practice it with the tasks for the video How Fire Burns .
  • What are the three conditions for a fire to start?

    Hints

    Remember the experiment with the candle and the glass over it. What was there in the glass?

    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 it takes for a fire to start.

    It takes a certain ignition temperature for the flammable material to catch fire.

    Not all substances burn. These are called non-flammable materials.

    Remember the 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

    Flammable and non-flammable materials are different.

    Flammable materials, like cooking oil and plastic, burn easily.

    Non-flammable materials, like glass and steel, do not catch fire.

    Solution

    Wood, cotton, plastic, gasoline, cooking oil, and hand sanitizer are some examples of flammable materials.

    Rocks, glass, copper, and water are examples of non-flammable materials.

  • Fire dangers: What should we do to make cooking enjoyable and safe?

    Hints

    Using a heat insulator like mittens will protect you from getting burned by handling hot items.

    Always have an adult to help you in the kitchen!

    Only adults should handle the oven, stove, and sharp items in the kitchen.

    There is more than one correct option here.

    Solution

    To make cooking enjoyable and safe, all of these items are important!

    1. Always ask an adult for permission to cook in the kitchen.
    2. Let an adult help with dangerous tasks such as using the oven, stove, and sharp kitchen items.
    3. Use oven mitts when handling hot pots, pans and baking trays.
    4. Have a safety checklist in the kitchen to help remind you of important safety rules!
  • What is true about fire?

    Hints

    These are the necessary conditions needed for a flame.

    Rocks are an example of non-flammable material.

    There are 2 correct answers.

    Solution
    • The two correct answers are:
    • The fire department should be called if there is a fire and Water or sand can help exstinguish the ignition temperature of a flame.

    The other two answers are incorrect because there are 3 necessary conditions to start a fire and rocks, glass, and water are non-flammable materials.

  • Can you use what you know to help the firefighter put out the fire?

    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 department 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 salt to cool it down.

    The water or salt that is used to extinguish the ignition temperature will also remove the oxygen in the flame.

    If the oxygen is removed or ignition temperature lowered, the flammable materials will not burn.