Definition
A way to put out a fire in oil by sealing off the air path with a lid, a damp towel, or something similar, so no oxygen can get in. With oil fires, where water makes a huge explosion, cutting off the fire's breath is the key principle for putting it out quickly and safely.
Why does water turn an oil fire into a giant pillar of flame?
When a pan catches fire while you're grilling pork belly or deep-frying, it's easy to panic and splash water from the sink. But pouring water on an oil fire is not just fanning a fire. It is like setting off an oil bomb. Water is heavier than oil, so the moment you pour it in, it sinks straight to the bottom of the hot oil.
Down there, the water meets oil boiling at hundreds of degrees, and in less than a second it turns into steam. When water changes from liquid to gas, its volume explodes outward to about 1,700 times bigger. That huge burst of steam pushes the burning oil above it out in every direction and instantly creates a giant pillar of flame and a storm of fire.
In the end, the water you meant to put out the fire acts like a detonator. It scatters tiny burning droplets of oil into the air, where they suddenly meet oxygen. To prevent a disaster where fire races through the whole kitchen, always remember to keep even a single drop of water away from an oil fire.
How smothering works: plugging the fire's air hole
You may have seen a candle go out after you turn a clear glass over it. For a fire to burn strongly, it needs oxygen from the air to keep arriving, besides fuel and high heat. Oxygen makes up around 21% of the air, and when that drops to 15% or lower, the fire loses strength and dies out on its own.
Smothering means exactly that: cutting off the oxygen the fire needs to breathe so it fades away by itself. When an oil fire starts, the fastest and surest move is to slide a metal lid that fits the pan over it gently from the side. Just sealing the opening so no air gets in uses up the oxygen inside the pan very quickly, and the fire goes out.
One thing to be careful about: even when you can't see flames, don't lift the lid right away. If the oil is still hotter than its ignition point, the temperature at which it catches fire on its own, fresh oxygen rushes in the moment you open the lid and the flames come back. It is safe to leave the lid on and wait quietly until the pan has cooled down.
What to do right in the kitchen, and the Class K extinguisher
If you can't see a lid that fits the pan right now, other things you can easily find in a kitchen can also block the oxygen. A large towel or dishcloth soaked in water and wrung out until it no longer drips, then laid gently over the whole pan, works very well. A thick, damp cloth forms a shield against oxygen and calms the flames in one go.
Dumping a big handful of broad, watery leafy greens, such as cabbage leaves or lettuce, into the pan is also useful. The cold vegetables do two jobs at once: they quickly take heat from the oil and lower its temperature, and they cover the oil's surface to cut off oxygen. And never forget to turn off the gas burner or induction cooktop first.
To be a bit more precise, the extinguisher made for cooking oil fires is the kitchen-only Class K extinguisher. In Korea, restaurant kitchens are required to have at least one. The agent in a Class K extinguisher forms a thick, sticky soap-like foam layer the moment it touches the oil's surface. This cuts off oxygen and cools the oil quickly, which helps prevent reignition. If you only put out the surface flames with a regular dry-powder extinguisher, the oil is still hot and can easily catch fire again.
Common misconceptions
When oil catches fire, a small splash of water will easily put it out.
Water sinks under the oil, turns to steam in an instant, and expands 1,700 times. It sends the burning oil flying in every direction and causes a huge fireball.
As soon as the flames are out of sight, you should lift the lid to let the air out.
If the oil is still above its ignition point, lifting the lid lets oxygen back in and the fire comes back to life. Keep the lid on until the pan has cooled down completely.
Where you meet it
While deep-frying, the pan catches fire, so you turn off the gas, cover it with a pot lid, and wait until it cools down
A fire starts in the kitchen, and instead of throwing water, you spread a large wet towel over the whole pan to put it out
In one sentence
Pouring water on an oil fire makes it explode, so put it out by smothering: cut off the air with a lid or a wet towel to remove the oxygen.