How does water put out fire?
In: Chemistry
Well you see, water is like a fire bully. It comes around and overwhelms the fire and steals it’s lunch money. At this point the fire is so sad that it disappears, leaving nothing but a triumphant puddle with $3.50.
Several ways, primarily fires are hot and need to be hot in order to continually burn, water has an extremely high specific heat capacity – https://youtu.be/18pK7rPtAAk basically it takes a lot of energy to raise the temperature of water. So putting water on a fire cools it down to a level where the fire can’t continue to burn. In addition water if applied in enough quantity and possibly when treated so it turns into foam it can blanket the source of the fire and prevent the fuel from gaining access to oxygen, this again stops the fire from burning.
Water wet, fire hot, wet > hot, water wins in correct ratio to fire. But if very small amount of water on big amount of fire then fire will win.
It interrupts the chemical reaction by creating a barrier between the fuel source and/or the oxygen source. It also has a cooling effect as water has a relatively low boiling point and is able to withstand relatively high heat. You should not use water to exstiguish a grease fire though, because grease floats on water and cannot effectively cause a barrier between the fuel source (oil/grease) and the oxidizer (air).
Edit: Fixed a typo.
It does it in two ways. Firstly it cools down the fire. When you put water and fire next to each other the heat from the fire will transfer into the water and the flames gets colder. It takes a lot of heat to get water to boil. This means that the flames do not have enough heat to ignite nearby fuel and the fire will stop spreading. The second way is that the water will soak any unburned fuel in the fire preventing the oxygen in the air to come in contact with it to catch it on fire. Even if the fuel is hot enough to burn it will not burn without oxygen. Without heat and without oxygen it does not take long for the fires to die down.
The fire triangle you learned in school is largely correct. Fuel + Oxygen + Heat => Byproducts of fire + More heat. The objective is to break down and separate that left side.
Water will tend to cool down the thing on fire and at the moment of contact blocks oxygen from reaching the fuel. Liquid water is always below 100 degC (212 degF), else it evaporates, which is usually low enough that things don’t burn.
At least for most types of fires. Electrical fires are causing heat from the electricity which water can conduct making it a bad choice for electrical fires. Fires when the thing on fire is also a liquid – eg: oil – is also bad because the water will just go into the oil, get super-hot, and boil itself instantly resulting in a hot flaming oil being thrown around especially upwards.
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