Why does putting water on a grease fire make it worse?

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Why does putting water on a grease fire make it worse?

In: Chemistry

The grease is burning _much_ hotter than the boiling point of water. When you throw water on it, the water flash-boils and turns to steam instantly. This causes the grease to get thrown into the air along with the steam, forming small grease droplets in the air. These grease droplets then catch fire, causing a large fireball which can cause the fire to spread out of control.

If you have a grease fire, you should use a fire extinguisher rated for grease (B rated – which most of the ones you can buy at stores are). If you don’t have one, kill the heat source and smother the fire with a pot lid.

The grease floats on top of the water And continues burning, meanwhile, the water explodes into steam underneath from the heat of the oil and spray s aerosolized flaming grease in a giant fireball at 400 degrees

The first thing to understand is that water and oil are immiscible- meaning they can’t mix due to their difference in polarities. Oil wouldn’t be able to bond to water unless the two hydrogen bonds on the oxygen were broken. These are too strong to be broken by the oil. To put it simply, the molecules of water and oil are very different and realized their lives would be better if they went their separate ways.

When the water is poured on the grease fire, the water actually sinks under the grease due to having a higher density, or being more heavy and compact than oil. Now that it is sitting under the grease, the water changes from a liquid to a gas (steam). It turns into steam instantly because water boils at a lower temperature than the oil fire. The resulting steam drags the grease with it and causes a big “uh-oh” because that grease fire is now being pulled into every direction except for the pan.

Other comments already explained that the very hot grease will simply evaporate the water instead of going out, causing a steam explosion that will spread the very-hot grease into the air as droplets. I wanted to add why exactly that is very bad. When grease burns, it means it combines the oxygen with the grease into CO2 (and others), which go back into the air. Since burning eats up the local Oxygen and replaces it with CO2, fires kinda suffocate themself a bit, limiting the amount of heat/energy produces. Also the grease is usually one big blob, where only the surface grease actually has contact with the air/oxygen.

Now when said steam explosion spreads all the grease in small droplets into the air, the grease is still hot enough to burn, but now each droplet is surrounded by lots of oxygen and they do not have to compete for it. This means all droplets immediatly burn alot more than they would have before, while being spread out everywhere. So basically the whole air in your kitchen explodes.

Water boils and grease goes from being in a pool to being strong independent greases.

Independent greases have more surface area.

Fire loves surface area.