What concept represents the heat, fuel, and oxygen needed for combustion?

• A. Fire triangle
• B. Fire tetrahedron
• C. Products of combustion
• D. Ignition

Answer: (A)

The idea being tested is that fire needs three ingredients: heat, fuel, and oxygen. This is represented by the fire triangle, a simple model that shows how combustion occurs only when all three elements are present. Heat keeps the fuel at its ignition temperature, fuel provides the material to burn, and oxygen supports the chemical reactions of combustion. Remove any one of these, and the fire cannot continue: cooling the fuel below its ignition temperature stops it, removing the fuel source starves the fire, and reducing or cutting off the oxygen supply suffocates it.

This model is distinct from the fire tetrahedron, which adds a fourth element—the chemical chain reactions that propagate combustion. It’s also different from products of combustion (the smoke, gases, and particulates left after burning) and ignition (the energy needed to start burning). The fire triangle specifically represents the three ingredients required for a sustained fire.