How does a chemical extinguishing agent affect flaming combustion?

• A. It forms an unstable product.
• B. It speeds the combustion reaction.
• C. It interferes with the chemical reaction.
• D. It burns more oxygen in a short amount of time.

Answer: (C)

Chemical extinguishing agents shut down the flame chemistry. In most flames, burning is sustained by a web of fast radical reactions involving species like H, O, and OH. The extinguishing agent releases substances that scavenge these radicals or otherwise disrupt the chain-branching steps, so there aren’t enough reactive radicals to keep the flame going. With the radical concentrations lowered, the chain reactions slow or stop, heat transfer is insufficient to sustain the flame, and the fire goes out. Some agents also form stable compounds that help this disruption, but the essential idea is interference with the chemical reactions that propagate combustion.