Activity: How does a fire extinguisher work?

Caution: This activity involves fire. For any activity involving fire you must have an adult present, plus water, a fire extinguisher and any other safety equipment you or the adult feel is needed. Take care to only use fire in a safe place.

You will need

• Matches
• Candle
• Vinegar
• Glass jar
• Spoon
• Bi-carb soda (Baking Soda) otherwise known as sodium bicarbonate
• Plasticine

What to do

1. Using the plasticine, stick the candle to the bottom of the jar. The top of the candle must be lower than the top or rim of the jar.
2. Sprinkle about three, heaped teaspoons of bi-carb soda around the candle.
3. With an adult's help or supervision, light the candle with a match.
4. Pour about half a cup of vinegar into the glass jar. The bi-carb soda should begin to froth, but be careful it doesn't froth over the candle.
5. Wait for a moment and the flame should go out.
6. Try to relight the candle with another match.

What's happening?

The chemical reaction, between vinegar and the bi-carb soda, produces bubbles of carbon dioxide gas. The carbon dioxide is invisible and heavier than air, so it collects in the jar but you won't be able to see it. The carbon dioxide fills the glass jar and covers the flame which cuts off the oxygen supply. Things only burn if they can get oxygen; if you take away the supply of oxygen, the fire will go out.

In order to understand how fire extinguishers work, you first need to know a little bit about fire.

Three things must be present at the same time in order to produce fire:

1. Enough oxygen to sustain combustion,
2. Enough heat to raise the material to its ignition temperature, and
3. Some sort of fuel or combustible material.

Oxygen, heat, and fuel are frequently referred to as the "fire triangle." The fourth element is the chemical, heat producing (exothermic) reaction that is fire. The important thing to remember is: take any of these three things away, and you will not have a fire or the fire will be extinguished.

Applications

Fire-fighters cover a fire with a layer of water, foam or carbon dioxide. This layer stops air and hence oxygen from reaching the flames, so the fire goes out. Essentially, fire extinguishers put out fire by taking away one or more elements of the fire triangle.

There are four common types of fire extinguishers: water, foam, dry powder and carbon dioxide. The dry powder and carbon dioxide extinguishers can be used for electrical fires. You can't use a water fire extinguisher on an electrical fire as water conducts electricity.

Another way to cut off the supply of oxygen to a fire is by using a fire blanket or throwing sand on a fire. If you go camping in an area where you are able to have a controlled camp-fire you will usually put the fire out by shovelling a bit of dirt on top.

Fires are extremely dangerous and unpredictable. Never fight a fire yourself you should always call for help.

Related Activities

Canister Rocket This link will show you the chemical reaction in this activity.