Welcome to Ask Professor Labcoat where Children’s Museum of Atlanta answers YOUR science questions!
One of our friends wants to know how does water put out a fire?
You might think that water and fire are opposites and that’s why water extinguishes fire. It makes sense, until you look a bit deeper at the chemistry underneath.
Fire is an example of a chemical reaction called combustion, which happens when oxygen gets very hot and meets a material that can burn, like the wood in your campfire. To put it simply, fire is basically oxygen exploding. But wait a minute… a water molecule is made of 2 hydrogen atoms and an oxygen atom. Shouldn’t that mean that water makes fire stronger? What is going on here?
Water cools and smothers the fire at the same time. It cools it so much that it can’t burn anymore, and it smothers it so that it can’t make any more of the oxygen in the air explode. You can also put out a fire by smothering it with dirt, sand, or any other covering that cuts the fire off from its oxygen source.
However, you can NOT put out a grease fire using water. A grease fire is oil that has caught fire. Water and oil do not mix, so throwing water on a grease fire only splatters the burning oil. Always use a lid to put out a stove fire.