Which class of fire can be extinguished with an H2O extinguisher?

The correct choice is that an H2O extinguisher is suitable for extinguishing Class A fires. Class A fires involve combustible materials such as wood, paper, and textiles. These materials can be effectively extinguished with water, which cools the fire and removes heat from the combustible materials.

Using an H2O extinguisher on Class A fires is appropriate because it can penetrate these materials and help to suppress the flames by soaking them, thereby preventing re-ignition.

In contrast, an H2O extinguisher is not suitable for Class B fires, which involve flammable liquids such as gasoline or oil, as water can spread the fire. Class C fires involve electrical equipment, and using water on these should be avoided due to the risk of electric shock.

Therefore, it's essential to understand the specific fire classifications when using extinguishers to ensure proper and safe fire-fighting measures.