What is a primary safety precaution when operating the APU on the C-130J?

Ensuring the area is clear of personnel is a fundamental safety precaution when operating the Auxiliary Power Unit (APU) on the C-130J. The APU generates power and provides bleed air for engine start and other pneumatic functions; therefore, it presents potential hazards such as noise, exhaust fumes, and rotating components. By keeping the area free from personnel, the risk of injury due to these hazards is significantly minimized.

Other options do not focus specifically on the immediate safety of personnel around the APU while it is in operation. Keeping cockpit doors open may not directly relate to APU safety, and while using protective eyewear can be important in many aviation tasks, it doesn't address the specific dangers associated with the APU itself. Checking fuel levels is also a necessary operational procedure but does not pertain directly to personnel safety during APU operation. Therefore, ensuring the area is clear of personnel is the most critical safety precaution in this context.