What is inerting used to achieve in a fuel tank?

• A. Increase oxygen to accelerate fuel combustion
• B. Seal the tank and ventilate with ambient air
• C. Create an oxygen-deficient, noncombustible atmosphere by introducing an inert gas to reduce oxygen to less than 1%
• D. Replace the fuel with an inert gas.

Answer: (C)

Inerting a fuel tank is about making the vapor space above the fuel nonflammable by removing most of the oxygen from it. By introducing an inert gas, such as nitrogen, the ullage atmosphere becomes oxygen-deficient, so there isn’t enough oxygen to support ignition if vapors are present. This is done to lower the risk of fire or explosion during operations like fueling, venting, or maintenance when vapors could accumulate. The goal is to keep the oxygen level in the tank’s ullage at a point where combustion cannot occur, which the answer frames as less than 1% oxygen.

Increasing oxygen would raise the flammability risk. Sealing and ventilating with ambient air would reintroduce normal oxygen levels, undoing the protection. Replacing the fuel with inert gas isn’t how inerting works in practice; the fuel remains, but the space above it is made inert to prevent ignition.