What does the negative pressure relief valve prevent?

The negative pressure relief valve is a critical component in an aircraft's cabin pressurization system. Its primary function is to prevent external pressure from exceeding internal pressure. This is particularly important during situations where the aircraft is flying at high altitudes and might encounter low external atmospheric pressures. If the cabin were to create a vacuum (negative pressure) due to rapid decompression or other factors, the negative pressure relief valve would open to equalize pressures and prevent structural damage to the aircraft.

Maintaining the balance between internal and external pressures is essential for the safety and integrity of the aircraft structure. Therefore, the valve acts as a protective mechanism to ensure that the pressures remain within safe operational limits, avoiding scenarios that could lead to potentially dangerous situations. The other answer choices do not accurately reflect the specific role of the negative pressure relief valve in managing pressure differences.