WEBVTT - How Do Fire Extinguishers Work?

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<v Speaker 1>Welcome to brain Stuff from How Stuff Works. Hey, brain stuff,

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<v Speaker 1>it's Christian Seger. Let's talk about fire. Fire is the

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<v Speaker 1>result of a chemical combustion reaction, typically between oxygen and

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<v Speaker 1>some sort of fuel like wood or gasoline. For the

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<v Speaker 1>reaction to occur, the fuel has to reach its ignition temperature.

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<v Speaker 1>For wood, that's about five hundred degrees fahrenheit or two

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<v Speaker 1>hundred and sixty degrees celsius. The heat decomposes some of

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<v Speaker 1>the woods cellulose, and the decomposed stuff is released as

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<v Speaker 1>volatile gases, like a compound of hydrogen, carbon, and oxygen.

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<v Speaker 1>When the gas is hot enough, its molecules break apart.

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<v Speaker 1>The atoms recombine with the oxygen to form water, carbon dioxide,

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<v Speaker 1>and other products. The heat keeps the fuel at the

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<v Speaker 1>ignition temperature, so it keeps burning as long as there

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<v Speaker 1>is fuel and oxygen. So there you have it. Fire,

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<v Speaker 1>the result of extreme heat, oxygen, and fuel. But what

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<v Speaker 1>about fire extinguishers? They remove at least one of these

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<v Speaker 1>elements from the equation. Fire extinguishers are metal cylinders filled

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<v Speaker 1>with water or smothering material, and when you depress a

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<v Speaker 1>lever at the top, the material is expelled by high pressure,

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<v Speaker 1>kind of like an aerosol. Can imagine a fire extinguisher

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<v Speaker 1>cut in half. Okay, that plastic siphon tube leads from

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<v Speaker 1>the bottom of the fire suppressant reservoir to the top

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<v Speaker 1>of the extinguisher. A spring mounted valve blocks the passageway

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<v Speaker 1>from the siphon to the nozzle, and at the top

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<v Speaker 1>of the cylinder there is a smaller cylinder filled with

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<v Speaker 1>compressed gas liquid carbon dioxide. For example, A release valve

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<v Speaker 1>keeps the compressed gas from escaping. When you pull out

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<v Speaker 1>the safety pin and depress the operating lever, it pushes

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<v Speaker 1>on an actuating rod. The rod presses the spring mounted

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<v Speaker 1>valve down to open up the passage to the nozzle.

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<v Speaker 1>The bottom of the actuating rod has a sharp point

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<v Speaker 1>which pierces the gas cylinder release valve. The compressed gas escapes,

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<v Speaker 1>applying downward pressure on the fire suppressant material. This drives

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<v Speaker 1>the material up the siphon and out the nozzle. The

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<v Speaker 1>proper way to use the extinguisher is to aim it

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<v Speaker 1>directly at the fuel, not the flames, and spray in

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<v Speaker 1>a sweeping motion. There are three main types of extinguisher.

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<v Speaker 1>A water extinguisher can put out things like burning wood, paper,

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<v Speaker 1>or cardboard, but it doesn't work well on electrical fires

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<v Speaker 1>or fires involving inflammable liquids. In an electrical fire, water

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<v Speaker 1>may conduct the current, which could electrocute you. Water will

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<v Speaker 1>only spread an inflammable liquid, making the fire worse. Then

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<v Speaker 1>there's the carbon dioxide extinguisher. The CO two is kept

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<v Speaker 1>in a pressurized liquid form. When the container is opened,

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<v Speaker 1>the CO two forms a gas. This gas is heavier

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<v Speaker 1>than oxygen, so it deplaces the oxygen surrounding the fuel.

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<v Speaker 1>This extinguisher is common in restaurants because it won't contaminate

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<v Speaker 1>cooking equipment or food. The most popular extinguisher material is

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<v Speaker 1>the dry chemical extinguisher. These cylinders contain foam or powder,

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<v Speaker 1>typically made of sodium bi carbonate also known as baking soda,

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<v Speaker 1>potassium bicarbonate, or mono ammonium phosphate. Baking soda starts to

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<v Speaker 1>decompose at only a hundred and fifty eight degrees fahrenheit

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<v Speaker 1>or seventy degrees celsius, and when it decomposes, it releases

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<v Speaker 1>c O two. The c O two, along with the

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<v Speaker 1>insulation of the foam, smothers fire. The best way to

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<v Speaker 1>tell which fire extinguisher you have and which fires it's

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<v Speaker 1>best suited to fight is to look at the rating.

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<v Speaker 1>All fire extinguishers have an A, B or C rating.

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<v Speaker 1>A Class A fire extinguisher works best against fires involving paper, wood, plastic,

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<v Speaker 1>and textiles. A Class B fire extinguisher can put out

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<v Speaker 1>flammable liquid fires you know, things like cooking oil, gasoline, paint,

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<v Speaker 1>or oil, and a Class CE extinguisher is your go

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<v Speaker 1>to for live electrical fires. Each extinguisher will have a

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<v Speaker 1>number by the letter indicating the size of the fire

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<v Speaker 1>that it can tackle, But please be careful. Most fire

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<v Speaker 1>extinguishers contain a small amount of suppressing. You can use

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<v Speaker 1>it up in seconds. That's why they're only effective on

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<v Speaker 1>relatively small fires. To put out a bigger fire, you

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<v Speaker 1>need more equipment like a fire engine, as well as

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<v Speaker 1>trained professionals. But for the blazes that can pop up

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<v Speaker 1>in your house, a fire extinguisher can be a lifesaver.

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<v Speaker 1>Check out the brainstuff channel on YouTube, and for more

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<v Speaker 1>on this and thousands of other topics, visit how stuff

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<v Speaker 1>works dot com.