What gas is commonly used as an expellant in stored-pressure fire extinguishers?

The use of dry nitrogen as an expellant in stored-pressure fire extinguishers is significant due to its non-reactive properties. It effectively helps to propel the extinguishing agent out of the extinguisher while maintaining the integrity of the contents. Nitrogen is ideal because it does not support combustion, making it a safe choice for fire suppression devices.

In contrast, other gases like carbon dioxide, while effective for some extinguishers, are primarily used as an extinguishing agent rather than as an expellant. Air, although it can be involved in the pressurization process, may contain moisture and impurities that can affect the performance of the extinguisher. Helium, on the other hand, is not commonly used in standard fire extinguishing applications due to its cost and availability, making dry nitrogen the preferred and practical choice for effective operation in stored-pressure extinguishers.