How Fires Are Put Out
A fire can only burn when fuel, oxygen, and heat are all present at the same time — the fire triangle. To extinguish a fire, you need to remove at least one side of that triangle. Every fire-fighting technique in existence — from blowing out a candle to a full fire-engine response — follows this same principle.
There are three fundamental strategies:
- Remove the fuel — stop the burning material from reaching the fire
- Remove the oxygen — smother the fire so it cannot get air
- Remove the heat — cool the fire below its ignition temperature
You do not need to do all three at once. Removing even one side of the fire triangle is enough to extinguish a fire. In practice, most extinguishing methods attack two sides simultaneously.
Strategy 1: Remove the Fuel
If you cut off the supply of fuel, the fire runs out of material to burn and goes out on its own.
Examples:
- Turning off a gas valve stops natural gas from reaching a burning hob
- Firefighters create firebreaks in forests by cutting or burning strips of vegetation ahead of a wildfire — when the fire reaches the cleared zone, it has nothing left to burn
- Moving flammable materials (curtains, paper, clothing) away from a small fire
This strategy is especially useful for gas fires and wildfire management.
Strategy 2: Remove the Oxygen (Smothering)
Cutting off the air supply starves the fire of the oxygen it needs. This is called smothering.
Methods of smothering:
- Carbon dioxide (CO₂) — CO₂ is heavier than air and settles over the fire, displacing oxygen. CO₂ fire extinguishers work this way.
- Sand — pouring sand over a fire covers it and cuts off air contact
- Foam — foam extinguishers coat the burning material with a thick layer that seals it from the air
- Fire blanket — a sheet of fire-resistant material placed over a burning pan or small fire, blocking all airflow
Real world: Putting out a chip pan fire
If oil in a pan catches fire, a fire blanket is the safest response. You carefully lay the blanket over the pan and leave it — the blanket cuts off oxygen and the fire goes out within seconds. Never use water on an oil fire: the water instantly vaporises, explodes outward, and spreads burning oil in all directions.
Never put water on an electrical fire or an oil fire. Water conducts electricity (danger of electrocution) and causes oil fires to explode violently. Always identify the type of fire before choosing an extinguisher.
Strategy 3: Remove the Heat (Cooling)
Water is the most common fire-fighting agent. It works primarily by cooling — absorbing enormous amounts of heat as it evaporates, dropping the temperature of the burning material below its ignition point.
Water also helps in a secondary way: the steam produced can slightly dilute the oxygen around the fire. However, cooling is the main mechanism.
Types of Fire Extinguishers
Different fires require different extinguishers. Using the wrong type can be useless — or even dangerous.
| Extinguisher Type | How It Works | Suitable For | Not Suitable For |
|---|---|---|---|
| Water | Cooling | Paper, wood, textiles (Class A) | Electrical, oil fires |
| CO₂ | Smothering with carbon dioxide | Electrical equipment, flammable liquids (Class B, E) | Large outdoor fires |
| Foam | Smothers and cools | Flammable liquids like petrol (Class B) | Electrical fires |
| Dry powder | Smothers and interrupts combustion | Most fire types (A, B, C) | Enclosed spaces (leaves residue) |
| Wet chemical | Cools and reacts with burning oil | Cooking oil fires (Class F) | Electrical fires |
Fire extinguishers are colour-coded in most countries. In Europe: red body for water, black label for CO₂, cream label for foam, blue label for dry powder. Check the label before use!
Matching Extinguisher to Fire Class
Fires are classified by what is burning:
| Fire Class | What Burns | Recommended Extinguisher |
|---|---|---|
| Class A | Solid materials (wood, paper, fabric) | Water, foam, dry powder |
| Class B | Flammable liquids (petrol, oil) | Foam, CO₂, dry powder |
| Class C | Flammable gases (propane, methane) | Dry powder; shut off gas supply |
| Class E | Electrical equipment | CO₂, dry powder |
| Class F | Cooking oils and fats | Wet chemical extinguisher |
Real world: CO₂ extinguishers in computer rooms
Schools and offices keep CO₂ extinguishers near computers and electrical equipment. If a computer catches fire, a water extinguisher would destroy the equipment and risk electrocution. CO₂ smothers the fire without leaving any damaging residue — once it evaporates, the equipment can sometimes even be repaired.
Fire Safety at Home and School
Most fire accidents can be prevented with a few basic habits:
- Never leave cooking unattended — kitchen fires are the most common cause of house fires
- Keep a fire blanket in the kitchen — it is the safest and fastest response to a small pan fire
- Do not overload electrical sockets — overloaded sockets cause electrical fires
- Know where your fire extinguisher is — and make sure it is the right type for your environment
- Close doors at night — a closed door slows the spread of fire and smoke significantly
- Know your escape route — practice what you would do in a fire before one ever happens
Practice Problems
A fire breaks out in a computer lab. Which type of extinguisher should be used and why?
Show answer
Explain how a fire blanket extinguishes a small pan fire, using the fire triangle.