Fire extinguishers are classified according to the materials they contain, and the types of fires you can extinguish with those materials. 

There is a class of fire extinguisher for each class of fire.

• Class A: Extinguishes ordinary combustibles (e.g., wood, paper)
• Class B: Extinguishes flammable liquids (e.g., grease, gasoline and oil)
• Class C: Extinguishes only electrically energized fires
• Class D: Extinguishes flammable metals (e.g., sodium, potassium)
  
• Class K: Wet chemical (especially for commercial kitchens)

These classes can be combined, to extinguish multiple types of fires:

• Class A, B, C: Multipurpose dry chemical extinguishers effective on A, B, and C fires
• Class B, C: Carbon dioxide extinguishers effective on B and C fires