What precaution should be taken during APU fuel servicing?

Ensuring no ignition sources are nearby during APU fuel servicing is crucial for safety. Fuel is highly flammable, and any ignition source can lead to a fire or explosion, especially in the vicinity of the auxiliary power unit (APU) where fuel vapors may accumulate. By maintaining a safe distance from sources of ignition, such as open flames, electrical sparks, or hot surfaces, personnel can significantly reduce the risk of fire during the refueling process. This precaution aligns with standard safety protocols to protect both the personnel involved and the aircraft from hazardous incidents.

The other options, while relating to safety, either do not directly address the primary concern of preventing ignition during fueling or may introduce risks rather than mitigate them. For instance, wearing fireproof gear is important for general safety but does not prevent ignition sources from causing an incident. Allowing the engine to run during refueling could dangerously increase the likelihood of an ignition event. Lastly, using manual fueling methods might not inherently affect safety but does not contribute to minimizing ignition sources.