Which gas is used for purging an aircraft fuel tank?

The most suitable gas for purging an aircraft fuel tank is nitrogen. This inert gas is used to displace the oxygen in the tank, thereby reducing the risk of combustion and preventing the formation of flammable mixtures. Nitrogen helps ensure that any residual vapors from fuel are safely removed.

When purging a fuel tank, it is crucial to use a gas that will not react with fuel or create hazards, and nitrogen serves this purpose effectively. Its inert nature means it does not support combustion, making it ideal for use in environments where fuel vapors may be present.

In contrast, gases like helium, carbon dioxide, and oxygen do not provide the same level of safety or suitability as nitrogen. Helium is not commonly used in such applications due to its cost and availability. Carbon dioxide might create pressure buildup in the presence of fuel vapors and is not inert concerning fuel reactions. Lastly, using oxygen in the purging process poses significant risks as it can lead to an increased chance of fire or explosion when present in the tank.