Which situation would necessitate the use of a Class B fire extinguisher?

The use of a Class B fire extinguisher is specifically designed for fires that involve flammable liquids, gases, and greases. This includes fires caused by petroleum products such as gasoline, oil, and solvents. The extinguishing agents in Class B extinguishers, typically foam, dry chemical, or carbon dioxide, work effectively by smothering the fire and depriving it of oxygen, preventing spread, and cooling the burning liquid.

Fires from combustible metals, such as magnesium or sodium, require a different approach, typically needing a Class D extinguisher due to their unique burning characteristics and the fact that they can react with water. Electrical fires are treated with Class C extinguishers to prevent electrical shock and because they require non-conductive agents. Fires involving wood or paper are classified as Class A fires and are typically handled with water or Class A specific extinguishing agents. Thus, the choice of a Class B extinguisher is essential for safely combating petroleum fires.