Which phenomenon occurs when fuel and air are mixed with a heat source, resulting in fire?

The correct answer, combustion, is a fundamental process in fire dynamics. Combustion is the chemical reaction that occurs when a fuel reacts with oxygen in the presence of heat, producing heat and light, which we observe as fire. This process requires three essential elements: fuel, an oxidizing agent (usually air), and heat, often referred to as the fire triangle.

In contrast, backdraft refers to a sudden explosive ignition of gases in a fire that occurs when oxygen is reintroduced into an environment that has been depleted of it, often after a door is opened or a window breaks. Flashover is a rapid spread of fire that occurs when all combustible materials in a room reach their ignition temperature, usually leading the entire room to ignite almost simultaneously. Flame spread describes how flames propagate over surfaces or through combustible materials, leading to an increased area of burning. Each of these terms describes different phenomena related to fire behavior and spread but does not define the reaction that actually constitutes fire, which is combustion.