When an oil fire has been extinguished, the surface of the oil should be kept covered with foam to prevent __________.

Correct Answer: Option B — air from contacting the oil vapors permitting reignition

Foam acts as a physical barrier that smothers the fire by excluding oxygen and cooling the fuel surface. Maintaining this blanket is critical because even after the flames are extinguished, the hot oil can reignite if exposed to atmospheric oxygen, leading to rapid re-flash of the fuel vapors.