What additional items are required for annual maintenance on carbon dioxide extinguishers?

For annual maintenance on carbon dioxide extinguishers, the need for a conductivity tester and a conductivity test label is particularly important. Carbon dioxide extinguishers work by displacing oxygen to extinguish fires, and ensuring that the electrical conductivity of the extinguisher is within safe limits is critical, especially since CO2 can be used for electrical fires. The conductivity tester helps in verifying that the extinguisher can safely be used in environments where electrical hazards are present. Additionally, the conductivity test label serves as documentation to confirm that the tests have been carried out and that the extinguisher meets the necessary safety standards.

The other options pertain to different maintenance processes or equipment that may not be specifically required for carbon dioxide extinguishers. For example, hydrostatic testing equipment is relevant for testing the structural integrity of various types of extinguishers but isn't unique to CO2 models. Similarly, while pressure gauges and nozzle inspections are important for many types of extinguishers, they are not the specific items required for the annual maintenance of carbon dioxide extinguishers.