How much air must be delivered to the intake if a bleeder return is closed?

In underground mining operations, proper ventilation is crucial for maintaining a safe environment by controlling the concentration of harmful gases and ensuring an adequate supply of fresh air for workers. When a bleeder return is closed, it can significantly affect the overall airflow in the mine.

The correct answer indicates that in such a scenario, 20,000 cubic feet per minute (CFM) of air must be delivered to the intake. This quantity is likely determined based on factors such as the size of the mine, the number of workers, the machinery in operation, and the types of gases that may accumulate in the absence of the bleeder return. Ensuring that this amount of air reaches the intake helps to mitigate the potential buildup of dangerous gases like methane and carbon monoxide, which can arise from mining activities.

The specific CFM value required helps miners and operators to maintain compliance with ventilation standards and safety regulations, which dictate the necessary air quality levels to protect workers' health and safety. Understanding these requirements is essential for an underground mine foreman, who is responsible for the operational safety and efficiency of mining activities.