What is the minimum depth threshold at which the mechanically produced air current becomes a requirement?

• A. More than 300 meters
• B. More than 100 meters
• C. More than 500 meters
• D. More than 600 meters

Answer: (A)

This question tests understanding of when mine ventilation must be mechanically produced rather than relying on natural air movement. In deep or extended mine workings, the air that naturally flows through the drift can become unreliable as distance increases, because friction, resistance, and changes in cross-section reduce velocity and the ability to dilute hazardous gases and heat. When the working area is more than 300 meters away, natural drafts generally aren’t sufficient to maintain safe air quality and adequate changes per hour, so a mechanically produced air current (fans and ducts) is required to guarantee proper ventilation. Shorter distances can often be ventilated adequately by natural means, while very long or deep workings would demand mechanical ventilation, but 300 meters is the minimum threshold specified for requiring forced ventilation.