Quick answers
What is the fire triangle?
It shows the three things a fire needs to start and keep burning: fuel, heat and oxygen. Take away any one of them and the fire cannot start, or it goes out.
What is the difference between the fire triangle and the fire tetrahedron?
The tetrahedron adds a fourth part, the chemical chain reaction that keeps the burning going. Some extinguishers, such as dry powder, work mainly by breaking this chain reaction.
How does a fire blanket or lid put out a pan fire?
It covers the fire and cuts off its oxygen, which breaks the oxygen side of the triangle. Leave it in place until the pan has cooled completely.
Why should water not be used on an electrical fire?
Water conducts electricity, so it can give you a shock. Switch off the power first if you can do it safely, and use an extinguisher whose label says it is suitable.
Why should water not be used on burning oil?
Water sinks under the hot oil, turns to steam in an instant and throws burning oil out of the pan.
Every fire, whether it starts with a matchstick, a kadhai of oil or a godown full of cartons, needs three things: something to burn, enough heat and oxygen from the air. This is the fire triangle. Once you understand it, most fire safety advice starts to make sense, from keeping a lid next to the stove to never throwing water on burning oil.
What is the fire triangle?
The fire triangle, also called the combustion triangle, shows the three things a fire needs to start and to keep burning:
- Fuel: anything that can burn, such as wood, paper, cloth, cooking oil or plastic.
- Heat: the energy that starts the fire and keeps it going, from a flame, a spark, a hot surface or an overheated wire.
- Oxygen: from the air around us, which feeds the burning.
All three have to be there together, in the right mix. Take away any one of them and the fire cannot start, or it goes out.
The fire tetrahedron: a fourth side
The triangle was later extended into the fire tetrahedron, which adds a fourth part: the chemical chain reaction that keeps the burning going once it has started. This matters because some extinguishers, such as dry powder, work mainly by breaking that chain reaction rather than by cooling or smothering.
How to break the triangle
Take away the fuel
Keep things that burn away from heat: cloth, paper and plastic away from the stove, heaters and lamps, and kerosene well away from any flame. When you build or furnish, choose fire-resistant materials where you can, so there is less to burn.
Take away the heat
Water cools a fire, which is why it works on wood, paper and cloth. Water-based extinguishers, including water mist types, work the same way. Switching off the gas or the electricity, when you can reach the switch safely, also takes away the heat source.
Take away the oxygen
Covering a fire cuts off its air. A fitting lid or a fire blanket can put out a small pan fire this way. Carbon dioxide and foam extinguishers also work largely by shutting out oxygen. Closing the door on a burning room slows the fire for the same reason, while opening a window can feed it.
Why it matters when you choose an extinguisher
Each type of extinguisher attacks a different side of the triangle, so the type has to match the fire. Indian Standards group fires into classes: A for ordinary solids like wood and paper, B for flammable liquids, C for gases, D for burning metals and F for cooking oils and fats. Check the label for the classes it covers before you buy or use one.
Water is the wrong choice in two common cases. On live electrical equipment it can give you a shock, and on burning oil it turns to steam and throws the burning oil out of the pan. With an electrical fire, switch off the power first if you can do it safely.
Try this in your kitchen
Look for the three sides. The gas flame is the heat, the oil in the kadhai is the fuel, and the air is the oxygen. Now find the lid that fits your kadhai and keep it next to the stove. That lid is how you take away the oxygen if the oil ever catches fire. If a fire grows beyond what a lid can cover, get out and call 101 or 112.
What needs attention
- A fire needs fuel, heat and oxygen; take away any one and it goes out
- The fire tetrahedron adds a fourth part, the chemical chain reaction, which some extinguishers interrupt
- Each extinguisher works by attacking one side: water cools, CO2 and foam smother, powder breaks the chain reaction
- Water on a live electrical fire risks electrocution
- A lid or fire blanket on a pan fire works by cutting off oxygen
Controls that reduce risk
- Keep fuel away from heat: cloth, paper and plastics clear of stoves, heaters and lamps
- Switch off gas and power to remove the heat source when it is safe
- Keep a lid or fire blanket near the stove to cut off oxygen
- Choose extinguishers that match the fires you could have
- Teach the fire triangle to children and staff with simple examples
Common unsafe practices
- Storing fuel, such as cloth, paper or kerosene, next to a heat source
- Throwing water on burning oil or a live electrical fire
- Opening a window or door to a room fire, which feeds it more oxygen
- Lifting a lid off a pan fire too soon, letting air back in
- Choosing an extinguisher without checking what fires it is meant for
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