Which of the following should not be used during fueling operations?

Cellular telephones should not be used during fueling operations due to the potential hazard they pose in terms of ignition sources. Fueling environments are highly flammable, and any electronic device that produces a spark, including cell phones, could ignite vapors released during the fueling process. The interference from signals and the possibility of sparks make their use prohibited to maintain a safe working environment.

In contrast, walkie-talkies are specifically designed for use in hazardous environments and often have features that mitigate the risk of ignition. Cameras, while they may also be seen as potential hazards, are generally not as dangerous as cellular phones in such situations. Fuel gauges are essential for ensuring the proper amount of fuel is used and managing the fueling process safely, and they do not pose an ignition risk.