A Class B foam extinguisher is not effective on which fuel?

• A. Gasoline
• B. Cooking Oil
• C. Alcohol-Based Fuels
• D. Diesel

Answer: (B)

Foam extinguishers create a foam blanket that cools the liquid and keeps vapors from escaping, which works well for hydrocarbon fuels like gasoline and diesel. Cooking oil fires, however, are fats/oils that burn at very high temperatures and can be difficult to suppress with a foam blanket—the oil can burn through the foam, spread, or re-ignite as the heat remains intense. For cooking oils, Wet Chemical extinguishers (Class K) are preferred because they react with fats to form a soapy layer that cools and separates the oil from the flame. So, a Class B foam extinguisher isn’t effective on cooking oil fires, making cooking oil the best choice.