How do dry chemical fire extinguishers work?

Three elements create a fire. Discover what they are and how dry chemical fire extinguishers combat them in this podcast from HowStuffWorks.com.

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Episode Transcript

Speaker 1 (00:00):
Welcome to brain Stuff from house stuff Works dot com
where smart Happens Hi Immercial Brain with today's question, how
do dry chemical fire extinguishers work? If you ask any
firefighter what it takes to create a fire, you will

(00:22):
learn that you have to have three things. First, you
need a fuel. You need some sort of combustible solid
liquid or gas. Next, you need oxygen to react with
the fuel, and finally, you need heat. There must be
enough heat to get the fuel above its flashpoint. If
there is paper on your desk right now, that's a

(00:43):
fuel and it's surrounded by oxygen, but it does not
burn unless you get the paper hot enough. If you
want to put out a fire, you need to remove
one of those three elements. When you watch firefighters battling
a forest fire, they generally try to remove fuel or heat.
Either they pour water on the fire to reduce the temperature,

(01:03):
or they try to bulldoze strips of bare earth to
eliminate the fuel. A carbon dioxide fire extinguisher works by
eliminating oxygen and replacing it with carbon dioxide. You can
do the same thing with just about any non oxidizing
gas nitrogen, for example, but carbon dioxide is inexpensive and

(01:24):
easy to store. Another way to cut off oxygen is
to throw a blanket over the fire. Covering the fire
with dirt or sand does the same thing as a blanket.
You might have heard that you can put out a
kitchen fire by throwing baking soda or salt on the fire.
Throwing sand would do the same thing, but most people
have more salt in their kitchens than they have sand.

(01:46):
Baking soda also releases carbon dioxide when it gets hot,
so that makes it even more effective. A dry chemical
fire extinguisher is essentially just a fancy way of throwing
baking soda on a fire. Dry chemical fire extinguishers are
by far the most common fire extinguishers in the home.
They can handle all three types of fires that you

(02:08):
would find in a kitchen or workshop, combustible solids like water, paper,
combustible liquids like gasoline or grease, and electrical fires. The
idea behind a dry chemical fire extinguisher is to blanket
the fuel with baking soda. A dry chemical extinguisher sprays
a very fine powder of sodium bicarbonate, which is baking soda,

(02:31):
or potassium bicarbonate, which is nearly identical to baking soda
or mono ammonium phosphate, and these solids coat the fuel
to smother the fire. Do you have any ideas or
suggestions for this podcast? If so, please send me an
email at podcast at how stuff works dot com. For
more on this and thousands of other topics, go to

(02:53):
how stuff works dot com and be sure to check
out the brain stuff blog on the house stuff works
dot com home page. Bo