When might a mine require a higher quantity of air than usual?

A mine might require a higher quantity of air than usual when roof falls or water close a bleeder return because these situations create an immediate need for improved ventilation to ensure the safety of the workers and the overall mine environment. When the ventilation pathways are obstructed, stale air can accumulate, along with harmful gases that may pose serious health risks. The introduction of additional air is crucial for diluting any toxic gases and providing breathable air to the miners. This is particularly important in underground mining environments where oxygen levels can drop rapidly, and any disruption in airflow could lead to dangerous conditions.

In contrast, during regular operational hours, ventilation requirements might be stable and predictable based on the regulated airflow needed for the equipment and workforce. Following equipment failure, while ventilation could be impacted, the need for increased air might not be as critical unless the failure directly affects the mine's air management systems. Similarly, while weather emergencies can influence mine conditions, they typically do not create an immediate necessity for increased air like a physical obstruction would. Hence, the need for a higher air quantity is most acute when obstructions like roof falls or water block vital ventilation routes.