Which of the following is true about ventilation doors?

Ventilation doors play a crucial role in maintaining proper airflow in mines, which is essential for safety and health. They help to manage the flow of fresh air and the removal of harmful gases, dust, and other pollutants that can accumulate in mining operations.

The requirement that ventilation doors must be closed after every use is based on safety regulations designed to ensure that the controlled airflow is maintained. Leaving doors open can lead to a disruption in airflow patterns, potentially allowing harmful gases to accumulate in working areas or reducing the effectiveness of ventilation systems. Furthermore, open doors can compromise the intended directional flow of air, leading to increased hazards for miners.

The other options do not align with safe ventilation practices. Leaving doors open indefinitely or for the duration of the shift, for instance, ignores the necessity for continuous monitoring and adjustment of ventilation systems, which are critical to air quality and mine safety. Additionally, ventilation doors cannot be considered optional, even if manual control is present; the controlled and regulated ventilation is paramount for maintaining a safe working environment in mines.