Why You Should Never Put Water on a Grease Fire

Everyone is told the rule. Almost nobody is told the reason, and the reason is the part that makes it stick.

Water does not fail to extinguish burning oil. It actively makes the fire enormous, in less time than it takes to react.

The instinct is completely understandable. Water is what we put on fires, and there is a tap two feet away.

It is also why so many kitchen fires that could have ended with a lid end up as house fires, a pattern set out in the real ranked causes of kitchen fires.

Why should you never put water on a grease fire?

Because of a density difference and a phase change, in that order.

1. Cooking oil is less dense than water, so water poured into a pan of oil sinks immediately rather than sitting on top.
2. It arrives at the bottom of the pan, which is the hottest place in the system and well above 200 degrees Celsius.
3. The water flash boils on contact, converting to steam in a fraction of a second.
4. That steam tries to occupy roughly 1,700 times the space the liquid water did, and it is doing so underneath a layer of burning oil.
5. The expanding steam throws the oil upward as a fine spray, which massively increases its surface area.
6. Atomised oil in air ignites instantly, so what was a pan fire becomes a fireball.

The critical detail is that the steam forms under the oil, not on top of it. That is what turns a cooling attempt into a propellant.

Put a number on it. A single tablespoon of water flashing to steam tries to become roughly 25 litres of gas, instantly, inside your pan.

How big does the fireball actually get?

In fire service demonstrations, a cup of water thrown into a pan of burning oil reliably produces a fireball that reaches the ceiling and spreads across it.

It happens in about a second. There is no window in which you notice it going wrong and step back.

The consequences follow from that. Burning oil lands on cabinets, the cooker hood, curtains and worktops, so you now have several separate fires instead of one.

It also lands on the person who threw the water. Hot oil burns are deep and they land on the face, arms and hands, which is why fire services use this demonstration at all.

NFPA data has long shown that more than half of the people injured in home cooking fires were hurt while trying to fight the fire themselves. Water is a large part of that number.

Is a wet tea towel the same mistake?

Yes, and this one catches people who know the water rule. A damp cloth is water in a different shape.

Laying a wet towel over burning oil does two things at once: it puts water in contact with hot oil, and it puts a flammable cloth over an open flame.

The same applies to ice cubes, a glass of anything, a wet sponge, or moving the pan to the sink and turning the tap on.

Moving the pan at all is its own hazard. Burning oil sloshes, and carrying a flaming pan across a kitchen spreads fire along the route you walk.

A dry fire blanket is a different thing entirely and is fine. The word that matters in every case is dry.

What should you use on a grease fire instead of water?

Smothering, always. Take away the oxygen and the fire ends, and nothing gets thrown anywhere.

• Turn off the heat first. This is the step people skip, and it is the one that stops the oil getting hotter.
• Metal lid or baking sheet: slide it across from the side, keeping your hand and forearm behind it, never lower it from above.
• Fire blanket: dry, held with both edges wrapped around your hands, laid on from the near side.
• Baking soda: works on a small pan fire, and it takes a lot more than people expect, so use the whole box.
• Class K or dry chemical extinguisher: effective, and messy enough that it is a second choice behind a lid.
• Never flour, sugar, baking powder or rice. Fine organic powders can ignite in air rather than smother.

Once covered, leave the lid on. Lifting it to check reintroduces oxygen to oil that is still above its ignition temperature, and it relights.

Give it a genuine twenty to thirty minutes before you look. The full technique is in how to put out a grease fire without an extinguisher.

Does the rule apply to ovens, fryers and barbecues?

It applies to any burning oil or fat anywhere, and the response changes slightly by appliance.

• Oven fire: leave the door shut and turn the oven off. Opening it feeds the fire air and pulls flame out at your face.
• Deep fryer: the same physics with far more oil, so the fireball is bigger. Turn it off, cover it, do not move it.
• Microwave: keep the door closed, unplug it if you can reach the socket safely.
• Barbecue or outdoor fryer: close the lid and shut off the gas at the bottle. Never carry a burning turkey fryer.
• Chimney or flue fire: different fuel, same rule about water, and it is a call to the fire service, not a DIY job.

Outdoor turkey fryers are the worst version of this, because they combine a large volume of hot oil with a frozen bird that is full of ice.

That temperature is the reason a covered pan stays dangerous for a long time. The oil is far above the point where it will relight on contact with air.

It also explains why grease fires start with no spark at all. Oil left heating quietly reaches its own auto-ignition temperature and simply catches.

The warning signs run in order: shimmering, then wisps of smoke, then heavy smoke, then flame. The gap between heavy smoke and flame is often under a minute.

So the real decision point is at the smoke, not at the fire. Sliding the pan off the heat when it starts smoking ends the whole story before it begins.

What else makes a grease fire worse?

A short list, and most of them are instincts rather than decisions.

• Fanning it with a towel or a lid, which supplies air and spreads burning oil droplets.
• Opening a window next to the hob, which pulls flame sideways into curtains.
• Turning on the extractor hood, which draws flame and grease laden air into a duct lined with old grease.
• Carrying the pan anywhere at all.
• Waiting to call because it seems small. If it is not out in under a minute, get out and call.
• Lifting the lid too early, which is the most common way a fire that was already out comes back.

One more that costs money rather than skin. Do not start wiping the greasy residue afterwards with a wet cloth, because it smears, as cleaning soot off kitchen cabinets explains.

What if someone already threw water on a grease fire?

Then treat it as a house fire, not a cooking accident, even if it looks like it went out.

Get everyone out and call the fire service. Burning oil that has been sprayed around lands in places you cannot see, including inside the cooker hood and on top of cabinets.

For burns, cool with cool running water for twenty minutes and get medical help for anything larger than a palm, on the face, or on a child.

Assume the smoke damage is far wider than the burn damage. Atomised oil burning in open air produces heavy greasy residue that reaches the whole floor.

Once it is safe, work through what to do after a kitchen fire in order rather than starting to clean.

How do you make sure it never gets that far?

By treating hot oil as an appliance that needs watching, not as a background task.

Keep a correctly sized metal lid within arm's reach whenever you fry, and know where it is before you turn the hob on.

Stop heating at the first wisp of smoke. Smoking oil is the warning stage, and it usually comes less than a minute before ignition.

Never leave frying unattended, not even to answer the door, which is covered in why you should never leave the stove unattended.

And keep a fire blanket in the kitchen rather than an extinguisher if you only have room for one. It is faster, calmer, and there is no wrong way to hold it.

Keep reading

PreventionHow to Put Out a Grease Fire Without an ExtinguisherPreventionHow to Prevent a Kitchen Grease FirePreventionNever Leave the Stove UnattendedBy LocationWhat to Do After a Kitchen FireBy CauseGrease Fire Cleanup in the KitchenPreventionThe Number One Cause of Kitchen Fires