What is one of the important safety protocols for refueling an aircraft?

Grounding the aircraft during refueling is a crucial safety protocol because it helps prevent the buildup of static electricity, which can create a spark capable of igniting fuel vapors. When an aircraft is grounded, it allows for any static charges to safely dissipate into the ground, significantly reducing the risk of fire or explosion during the refueling process. This practice is part of standard procedures to ensure the safety of both the ground crew and the aircraft itself.

The other options present methods that do not contribute to safety during refueling. Ensuring maximum fuel capacity can be important for flight operations but does not directly address the hazards associated with refueling. Allowing passengers to board during the refueling process poses significant risks, as the presence of people can complicate safety measures and create additional hazards. Similarly, using regular household tools is inappropriate and unsafe for aircraft operations, which require specialized equipment designed for aviation fuel handling.