How are carbon dioxide extinguishers checked to determine if they are full?

Carbon dioxide extinguishers are checked for fullness primarily by weight. Each CO2 extinguisher is designed with a specific weight for the amount of carbon dioxide it contains. When inspecting the extinguisher, the technician checks the weight against the manufacturer's specifications. If the extinguisher is not at the indicated weight, it may be indicative of a leak or that it needs to be recharged.

Other methods such as checking by volume or pressure are not applicable to CO2 extinguishers, as they do not provide the necessary information for determining fullness. CO2 operates based on the fact that it is stored as a liquid under pressure, and once it is dispensed, it converts to gas. The pressure gauge is not a reliable method for measuring the fullness of these extinguishers, as the pressure could still read nominal levels even if the extinguisher is nearly empty, especially with regards to the effectiveness of discharge. Color is irrelevant in this case, as it does not determine the amount of CO2 contained within the extinguisher. Therefore, weighing is the most accurate method for ensuring the extinguisher is properly charged.