What is the Fire Triangle? A Guide to How Fires Start

Every fire on the planet, from a match striking a box to a warehouse ablaze, needs the same three things to burn. Take one of them away, and the fire goes out.

That's the principle described by the concept of the fire triangle. And it's the principle behind every fire extinguisher on the market: each one is designed to knock out a different side of the triangle.

Here's what each side is, why it matters, and how to use the triangle to make the right choice for your own fire control measures.

The three elements of the fire triangle

The fire triangle is the model used in the government's official fire risk assessment guidance for offices and shops to explain how fires start. It has three sides: a source of ignition (heat), fuel, and oxygen. If any one of them is missing, a fire cannot start.

Ignition/heat

A fire needs a heat source hot enough to set light to whatever's nearby. The same GOV.UK guidance flags several common ignition sources for offices and shops: cigarettes and matches, candles and other naked flames, portable heaters, cooking equipment, faulty or overloaded electrical kit, hot surfaces, and sparks from tools like welders and grinders.

Scorch marks on a plug socket, a charred lamp shade, a burnt patch on a workbench. These are the near misses that tell you where your ignition risks are.

Electrical distribution and appliances are the leading ignition source of fires, representing 25.2% of fires. Other sources of ignition include smoker’s materials like cigarettes, matches and lighters, as well as candles and other open flames.

Fuel

Fuel is anything that will burn. And in most premises, there's more of it than people realise. Paper, cardboard, wood and rubbish are obvious sources of fuel to a fire. But structural fittings are an abundant source of fuel too, representing 21.2% of “first ignited” materials. And, of course, furnishing, textiles, chemicals, all can feed and even accelerate the spread of a fire.

The more fuel you have in one place, and the closer it sits to a heat source, the greater the risk. That's why fire risk assessments spend so much time on housekeeping and storage.

Oxygen

Oxygen is the one you can't easily remove. It's already in the air around us, and per the guidance, the main supply is whatever comes in through open doors, windows, and ventilation systems.

But some workplaces have extra sources on site. Oxidising chemicals in cleaning cupboards. Oxygen cylinders used for welding or first aid. Pyrotechnics, if you sell fireworks. Any of these can help a fire burn hotter and faster than it would otherwise.

How breaking the fire triangle puts a fire out

Every fire extinguisher, fire blanket, and sprinkler head is doing one of three things: cooling the fire, smothering it, or starving it. Some do more than one at once. But the mechanism is always the same. Knock out a side of the triangle, and the fire dies. A fire with ignition and fuel cannot burn without oxygen. A fire with ignition and oxygen cannot burn without fuel. A fire with fuel and oxygen cannot burn without ignition or heat.

The GOV.UK guidance sets out which extinguisher type suits which fire, based on this exact mechanism.

Starving: removing fuel

While you can't spray a fire with fuel-removal, sometimes there are ways to stop the fire feeding on anything else.

The government’s guidance treats this as a preventative step. Turning off a gas supply is a sensible thing to do during a fire if it’s safe to do so. But no-one is suggesting you spend time on moving fuel out of a fire’s path instead of evacuating the premises.

Instead, your risk assessment will identify sources of fuel and its proximity to ignition sources, as well as identifying ways to slow the spread, like keeping fuel sources behind fire doors. The guiding principle is to reduce the fuel available to a potential fire, making the fire less likely to start or spread.

Cooling: removing heat

Cool a fire down and it can no longer burn. This is the technique behind water-based extinguishers: spraying water on burning wood or paper absorbs the heat and drops the temperature below the point at which the fuel can keep burning.

But water doesn’t mix with certain fire fuel types, like liquid or electrical fires. Here, the water either helps spread the fuel further or conducts the electricity back to the person holding the extinguisher. That’s why cooling is best reserved for fires that are using paper, textiles and wood as fuel.

Smothering: removing oxygen

Fire blankets, CO2 extinguishers, even foam extinguishers to an extent; they all act as a barrier between a fire and oxygen. Blankets and foam create a physical barrier that stops more oxygen reaching the fire. CO2 extinguishers flood the area with carbon dioxide instead, a gas that fire can’t use to keep burning.

Either way, once the fire has used all the oxygen it can reach, that side of the fire triangle collapses and the fire goes out.

How the fire triangle helps you choose fire safety equipment

The fire triangle is more than just theory: it can help you understand how fire safety equipment works and which is best for your fire safety strategy.

For example, if your main risk is paper and packaging, something that removes heat (like a water-based extinguisher) is a solid choice: water. If you have a lot of electrical equipment on your premises, you’ll need something that smothers without conducting electricity, like a CO2 extinguisher. If you’re working with flammable liquids, foam extinguishers will cut off the fire from oxygen while helping prevent the spread of those liquids.

Picking the wrong extinguisher can mean you can’t put out a fire or even make it worse. But once you understand the mechanism of the fire triangle, matching the extinguisher to the risk becomes much easier.

But if you're still not sure which extinguisher matches the risks in your building, take a look at our range of fire extinguishers or give our team a call on 0808 175 4375. We're happy to offer our advice and help you figure out exactly what you need.