Fire Basics

Understanding Fire

To fight fires, you need to understand how they ignite, what kinds of fire occur, and how to approach and extinguish each different type in a safe and effective way. 

 The fire triangle

The fire triangle is a simple model for understanding the necessary ingredients for most fires.

The triangle shows the three elements a fire needs to ignite:

  • heat

  • oxygen

  • fuel

A fire occurs when the elements are present and combined in the right mixture.

The Fire Tetrahedron

The fire tetrahedron is the fire triangle with a chemical chain reaction added.

Once a fire has started, the resulting exothermic chain reaction allows it to continue.

To stop the fire, you need to block at least one of the elements.

You can use foam to deny the fire the oxygen it needs.

You can use water to lower the temperature of the fuel below the ignition point or to remove or disperse the fuel.

You can use halon to remove free radicals. This creates a barrier of inert gas in a direct attack on the chemical reaction responsible for the fire.


Combustion is the chemical reaction that feeds a fire more heat and allows it to continue.

As soon you remove one of the four elements of the tetrahedron, combustion stops.

Classes of fire

  • Class A – fires involving solid materials such as wood, paper or textiles.

  • Class B – fires involving flammable liquids such as petrol, diesel or oils.

  • Class C – fires involving gases.

  • Class D – fires involving metals.

  • Class E – fires involving live electrical equipment.

  • Class F – fires involving cooking oils such as in deep-fat fryers.

Extinction of the fire

To stop a combustion reaction, you must remove one of the three elements of the fire triangle.

Without enough heat, a fire cannot begin, and it cannot continue.

Remove heat by applying a substance which reduces the amount of heat available to the fire. This is often water, which absorbs heat as it changes from water to steam. Also, using the right powder or gas reduces the amount of heat available for the fire.

Scraping embers from a burning structure also removes the heat source. Turning off the electricity in an electrical fire removes the ignition source.

You need to use different methods to extinguish the different classes of fire.

For example, if the fire contains burning metals like:

  • lithium

  • magnesium

  • titanium

It’s known as a class-D fire. Metals react faster with water than with oxygen and so release more energy. Putting water on a class-D fire means the fire will get hotter or explode. Carbon dioxide extinguishers are also ineffective against certain metals such as titanium. You must use inert agents (e.g. dry sand) to break the chain reaction of metallic combustion.

Free Fire Extinguisher Training Video

This video covers the basics of fire extinguishers. It talks more about the fire triangle, fire extinguisher types includes A, B, C, and D when to fight a fire versus when to evacuate.

You’ll also learn the PASS method for using a fire extinguisher:

  • Pull the pin

  • Aim the hose at the base of the fire

  • Squeeze the handle

  • Sweep