Basic Operations Firefighter Certification Practice Exam

Carbon dioxide extinguishers are generally rated for which types of fires?

1. Class A only

2. Class B and C

3. Class D only

4. Class B, C, and A

The correct answer is: Class B and C

Carbon dioxide extinguishers are designed to be effective primarily on Class B and Class C fires. Class B fires involve flammable liquids such as gasoline, oil, and grease, while Class C fires involve electrical equipment. The CO2 extinguisher works by displacing oxygen and cooling the fire, which is particularly suited for these types of fires where the use of water or foam could exacerbate the situation, especially in electrical and oil-related fires. The reason carbon dioxide extinguishers are not rated for Class A fires, which involve ordinary combustibles like wood, paper, and fabric, is that they are less effective in smothering the combustion reaction that takes place with these materials. Class D fires, involving combustible metals, require specific extinguishing agents that can handle the unique burning characteristics of metals. Thus, while carbon dioxide extinguishers are versatile, their primary use is restricted to the types of fires that are safe to manage using this gas, which is why they are rated for Class B and C situations.