Class A, B, C, D, and K Extinguisher Requirements A portable extinguisher must match the fire that is being fought. There are five classes of fires. Extinguishers are labeled with letters and symbols for the classes of fires they can put out. While these requirements apply to all portable fire extinguishers, different location requirements exist for Class A, B, C, D, and K extinguishers. Please refer above image for the explanation.