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Why water is the enemy of fire

From a young age, everyone know that water is the enemy of fire. But no one really goes on to explain why. Here it is important to mention that for various different reasons water is not suitable to put out all fires like oil fires or chemical fires, but water can kill some common ones like with paper or wood.

Firemen Blowing Water on Fire

The fire triangle

To answer the question of why water kills fire we first need to talk about the fire triangle. this is something that is used to illustrate the three major requirements for a fire, so for any fire to occur we need Oxygen, Fuel and Heat in every single case.

Why water is the enemy of fire

To stop a fire at least one of these elements should be removed. In the case that we use water to extinguish a fire, the heat is taken away. This is the fast and quick answer to our main question.

Activation energy and released energy

The fire and lot of reactions in general require something called activation energy which basically means that certain amount of energy is required for the reaction or the fire to start. So the initial energy breaks some molecular bonds, once these bonds are broken the atoms of the reactants are free to rearrange and form new products that are more stable.

The formed products are more stable which means they have less energy associated with the bonds between atoms. This difference in energy between the products and the reactants is released to the environment in the form of heat. It’s important to notice that the energy released is completely different from the activation energy, so even if the reaction overall releases a crazy amount of heat and energy it can start by giving it a small amount of activation energy.

Fire

In the case of fire the reactants are some sort of carbon-based fuel with oxygen, they react together to form a very stable carbon dioxide and water. This conversion from the less stable Fuel to the very stable carbon dioxide and water results in the release of energy. The main rule to get any fire going is to overcome the activation energy, once the fire gets started it becomes self-sustaining one fuel molecule reacting with oxygen releases enough Energy to cover the activation energy of the molecules around it so only one molecule needs to react to get multiple molecules around it reacting and this is one reason why fire can easily get out of control.

Why water can stop a fire ?

During a fire, if somehow it is possible to absorb enough energy that the fire can no longer provide its own activation energy it will no longer be Self-sustaining and it will die out. This is exactly what happens when water is putted on a fire.

Water basically has two major things:

  • It’s completely non flammable
  • it takes an insane amount of energy to vaporize it

The boiling point of water is much lower than the temperature of a fire so it immediately starts to boil. The amount of energy that’s required to convert water from a liquid to a vapor is actually huge.

The temperature of the average wood fire is between 400 and 600 0C but it needs to reach a temperature of at least 150 0C in order to overcome its activation energy, if water is added to this fire it would quickly start absorbing all of the energy and heat around it and converting to steam. The conversion of liquid water to vapour takes place at around 100 0C and it takes a lot of energy, That’s why a lot of the heat produced by the fire ends up being diverted into converting the water to steam.

A big amount of water should be added, which is too much for the fire to boil off, so the temperature of the wood or the fuel is going to be 100 0C or less, and this is at least 50 0C less than the activation temperature. Because the fire is no longer contributing the heat necessary to reach its activation temperature it just dies.

So the water brings the temperature of everything it touches down and absorbs a crazy amount of energy in order to be converted to steam, if the fire can’t provide enough energy to boil off the water and bring the fuel back up to its activation energy then the fire will be extinguished.