What does a number on the fire extinguisher mean?

The numbers on a fire extinguisher indicate its effectiveness against specific types of fires. For example, a fire extinguisher labeled with a number followed by a letter (like 2A or 4B) signifies its capacity to extinguish fires of certain classes, such as ordinary combustibles (A) or flammable liquids (B). The higher the number, the greater the fire-fighting capability of the extinguisher for that class. Always refer to the label for specific instructions and details on usage.