What is the purpose of reversible main fans?

Reversible main fans are designed primarily to allow for the reversal of air current during emergencies. This feature is crucial in underground mining operations, where conditions can change rapidly, and adequate airflow is essential for the safety of miners. In the event of an emergency, such as a fire or a buildup of hazardous gases in a particular section of the mine, being able to reverse the airflow can clear out harmful contaminants, improve visibility, and provide a safe exit route for workers.

The other options, although they may touch on aspects of ventilation, do not capture the primary function of reversible fans. Increasing air pressure can be achieved with different fan designs but is not the specific purpose of reversible fans. Improving ventilation efficiency can result from various factors, including fan design and installation, but it is not the main purpose. Reducing noise can be a benefit of fan design, but is not related to the reversal feature, and is not a primary function of these fans in emergency scenarios.