Recirculation in an auxiliary fan occurs when which condition?

• A. Exhaust air is drawn into the intake air.
• B. Fresh air is drawn into the intake air.
• C. Air is cooled in the intake.
• D. The fan stops moving air.

Answer: (A)

Recirculation in an auxiliary fan occurs when exhaust air is drawn back into the intake air. This backflow means contaminated, warm air from the underground returns to the surface intake instead of bringing in fresh air, reducing dilution and increasing exposure to contaminants. Fresh air entering the intake would not be recirculation, and cooling the air in the intake or the fan simply stopping would not cause this backflow.