In addition to electrical fires, what other type of fire can a CO2 extinguisher effectively extinguish?

A CO2 extinguisher is specifically effective in extinguishing liquid fires, particularly those involving flammable liquids like petrol, paint, and solvents. The way that CO2 extinguishes fires is by displacing oxygen around the fire, which is essential for combustion. When CO2 is deployed, it forms a cloud that suffocates the flames, effectively stopping the fire from continuing to burn.

In the context of the other options, solid fires typically involve materials like wood, paper, or textiles, which are better managed with water or other types of extinguishers. Flammable gases present a unique challenge, as they may require different extinguishing agents depending on the gas. Lastly, metal fires, particularly those involving combustible metals like magnesium or sodium, require special extinguishing agents that are not suitable for CO2. Thus, the effectiveness of a CO2 extinguisher primarily lies in its ability to handle liquid fires, making that the correct answer.