Why does adding water to an oil fire make it exponentially worse?
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That oil can get substantially hotter than the water is capable of. Water upon hitting the oil will turn to steam essentially on contact. Steam then rapidly expands, throwing globules of oil everywhere, which are likely still flaming. Even a small amount of water can wreak havok, sending oil flying everywhere.
You can see this effect pretty easily if you ever cook anything with oil. Steam from water in the food will cause the oil to spray up a fine mist, which then lands on the stove as those oily little beads that cover the surface of your stove when you’re done.
In a cooking oil fire, the oil is hotter than the boiling point of water.
Water heated past boiling turns into steam with a massive amount of volume increase.
Water is heavier than oil so it will sink to the bottom of the oil.
In a cooking oil fire, like frying something on the stove, only the top of the oil is exposed to air and on fire. Not ideal, but could be worse, at least the fire isn’t spread everywhere.
Add water -> water sinks -> water turns to steam -> steam causes hot flaming oil to spray everywhere.
Generally, if oil is on fire, it’s hot. Easily hot enough to boil water.
So you go from a vessel of extremely hot oil that is on fire, to a still very hot vessel of oil that is on fire and violently boiling over the edges of the vessel.
Burning oil in a big pot on the stove is bad.
Burning oil exploding all over your kitchen is worse.
Adding water to hot oil makes the water boil and do just that.
Also, oil floats on top of water so water can help the burning oil spread even if it doesn’t do it violently.
Burning oil is likely 200+ degrees, adding water boils it instantly and since oil is lighter than water it gets thrown into the air by steam, while still burning.
When you add water to a grease fire, it can make the fire worse because water and grease don’t mix. The water sinks to the bottom and turns into steam, which pushes the burning grease up and out of the pan, spreading the fire.
This is why they tell you to smother grease fires or use an extinguisher instead.
Oil only burns on the surface and at temperatures much higher than 100°C. When you pour water on it, it splashes in the oil and then almost instantly evaporates, so now you have a ton of gas inside the oil, which wants to rise up and escape. That rising water vapor will aerosolize the oil, cresting a ton of super hot oil droplets in the air. Those droplets have a much higher surface area than the oil previously had. These droplets are hot enough to ignite, cresting a fireball in the air above the oil.
This can even happen if the oil is just heated enough, not even burning yet.
To put out an oil fire, use a fire extinguisher rated for class B (or preferably class K) fires. You can also cover the fire with a lid if it hasn’t gotten too out of control yet. Baking soda on the fire also works well. Other kitchen powders (like flour) won’t work. Flour is extremely combustible.
The water rapidly (like almost instantly) boils and turns into steam. When water boils, the steam has about 1600x more volume than the liquid that boiled.
Water is also heavier than oil and will sink to the bottom. So it’s nearly an explosion. The water sinks beneath the oil and then gets blasted into steam with a 1600x volume increase. That means you just instantly generated several litres of gaseous steam underneath the flaming oil. The hot gas has to expand, exploding the still-flaming oil everywhere.
Fires that are extinguished by water have fuel that can mix with water. Water and oil don’t mix. When you put water on an oil fire, all that will do is splash the oil everywhere and make the fire spread.
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