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

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

Foam creates a physical barrier that separates the fuel surface from the atmosphere. This blanket prevents oxygen from reaching the fuel vapors, which is essential to stop reignition. If the foam blanket is broken, flammable vapors can escape and mix with air, creating a significant risk of fire recurrence.