All fires require three basic ingredients, one of which is fuel. What is another?

Fires require three essential components to ignite and sustain combustion, commonly known as the fire triangle. One of these components is fuel, which is the combustible material that burns. Another crucial ingredient is heat.

Heat serves as the energy source that initiates the combustion of the fuel. When a material is heated to its ignition temperature, it begins to burn. This process not only maintains the chemical reactions necessary for fire but also allows the release of more heat, which can ignite other combustible materials nearby, sustaining the fire.

In the context of firefighting and fire prevention, understanding the necessity of heat in the fire triangle is vital. By removing any of these components—fuel, heat, or oxygen—fires can be extinguished effectively. In this case, heat is the correct answer as it directly supports the combustion process alongside the fuel.