What must be included on portable fire extinguisher labels?

The correct answer emphasizes the necessity of having appropriate letters and/or symbols on portable fire extinguisher labels. These labels serve an essential purpose in providing critical information at a glance about the type of fire extinguisher and its intended use. The letters and symbols indicate the classes of fires that the extinguisher is designed to combat, ensuring that users can quickly and effectively choose the right one in an emergency situation. For instance, symbols may indicate suitability for flammable liquids, electrical fires, or ordinary combustibles, which helps in preventing incorrect usage that could lead to dangerous outcomes.

Including such standardized symbols and letters on labels assures that all users, whether they are trained personnel or the general public, can easily identify the extinguisher's functions and limitations. This is crucial for safety and effectiveness during fire emergencies.