What is the process in which fatty acids in the cooking medium react with the extinguishing agent and form foam or soapy residue?

• A. Vaporization
• B. Combustion
• C. Saponification
• D. Oxidation

Answer: (C)

Saponification is the process at play when fatty substances like cooking oil react with the alkali in certain extinguishing agents to form soap. Fats and oils are triglycerides; when a kitchen extinguisher containing a strong alkali (such as a wet chemical Class K agent) is applied, it hydrolyzes the triglycerides into glycerol and fatty acid salts—soap. That soapy layer creates a barrier on the surface, helps cool the fuel, and smothers the flame, which is why you see foam or a soapy residue after use. Vaporization, combustion, and oxidation describe other fire behaviors or chemical reactions that do not produce a soapy layer, so they aren’t responsible for the observed residue.