What should be used to inert an integral fuel tank before repairs?

The correct choice for inerting an integral fuel tank before repairs is nitrogen gas. Nitrogen is an inert gas that is non-flammable and does not support combustion, making it ideal for displacing oxygen in fuel tanks where flammable vapors may be present. This process significantly reduces the risk of fire or explosion during maintenance operations.

Using carbon dioxide (CO2) for inerting is not recommended due to its ability to form carbonic acid in the presence of water, which can lead to corrosion in the tank. Additionally, CO2 is not entirely inert under all conditions and may not be as effective as nitrogen in preventing combustion.

Inert gases, such as argon, could theoretically be used; however, nitrogen is more commonly employed in aviation fuel tank inerting systems due to its availability, cost-effectiveness, and proven safety record. Using air is particularly dangerous, as it contains about 21% oxygen, which can catalyze combustion when in the presence of fuel vapors. Therefore, nitrogen remains the safest and most appropriate choice for this application.