Portable fire extinguishers are categorized based on which criterion?

Portable fire extinguishers are categorized primarily based on the type of fire they are designed to extinguish. This classification is crucial because different types of fires require different extinguishing agents. For example, Class A extinguishers are suitable for ordinary combustibles such as wood and paper, while Class B extinguishers are intended for flammable liquids. Class C extinguishers are meant for electrical fires, and Class D extinguishers are used for metals. Recognizing the appropriate extinguisher type ensures effective and safe firefighting, preventing further risk of fire spread or injury.

Other options, while significant in their contexts, do not primarily dictate the categorization of fire extinguishers. Material composition may impact the effectiveness of an extinguisher but does not determine its designated class. Size and weight influence portability and the amount of extinguishing agent available but are not the basis for categorization. Similarly, the operating mechanism can vary, but this variance does not define the extinguisher's primary purpose or use in relation to specific fire types.