Which of the following is NOT a characteristic of mechanical ventilation?

Mechanical ventilation is characterized by its use of artificial methods to move air within an underground mine or tunnel system. This includes the utilization of fans to create airflow and the incorporation of air control devices to regulate that airflow.

When considering the options, relying on natural airflow distinguishes natural ventilation from mechanical ventilation. Natural ventilation occurs due to external influences such as wind or temperature differences, allowing air to move without artificial intervention. Thus, a key element of mechanical ventilation is its deliberate engineering to ensure sufficient and appropriate air movement for safety and operational efficiency. The other characteristics, such as using fans and including air control devices, are essential components of mechanical ventilation systems, which are designed specifically to enhance air circulation in environments where natural airflow is insufficient or unpredictable.