What happens when sufficient heat is applied to fuel and oxygen?

• A. Free radicals form and initiate a self-sustained chemical reaction.
• B. An unstable by-product forms and off-gases toxins.
• C. Free radicals form and retard chemical chain reactions.
• D. Particles form and bond with the fuel reducing the flammable range.

Answer: (A)

Heat provides the activation energy to start the oxidation of fuel by oxygen, breaking bonds and creating highly reactive free radicals such as hydrogen, oxygen, and hydroxyl. These radicals quickly engage in a network of chain reactions that produce more radicals and release heat, driving the flame forward. This self-sustaining sequence continues as long as there is heat, fuel, and oxygen present. The idea isn’t about unstable by-products or toxins forming at ignition, and radicals accelerate rather than retard the reactions. It also isn’t about particles bonding with fuel to change the flammable range; ignition is governed by radical-driven chain reactions that sustain combustion.