What is the required procedure to prevent fire or explosion during fueling?

The required procedure to prevent fire or explosion during fueling is to ensure proper bonding of the aircraft and the fueling unit. This process involves connecting a bonding wire between the aircraft and the fueling truck or tank, which helps to equalize the electric potential between them. This is crucial because static electricity can build up during fueling due to fuel movement and flow, which can lead to sparks and potential ignition sources. Proper bonding mitigates this risk by providing a safe path for static discharge, thus enhancing safety and reducing the likelihood of a fire or explosion.

While other options may contribute to safety during fueling, they do not address the specific electrical hazard created by static electricity as effectively as bonding does. For instance, disconnecting the fueling unit or limiting personnel are prudent safety measures but do not directly prevent static discharge risks. Similarly, fueling only during daylight hours may enhance visibility but does not address the underlying electrical hazards associated with fueling operations.