Final answer:
Portable CNG containers must not be stored when the capacity is greater than the designed limit to avoid safety hazards.
Step-by-step explanation:
Portable CNG containers must not be stored when the capacity is greater than the designed limit. These containers are designed to withstand a certain maximum pressure, and exceeding that pressure can lead to potential safety hazards. To determine the maximum capacity, engineers consider factors such as the structural strength of the container and the gas's behavior under different conditions.