Where must the concentration of methane, carbon monoxide, carbon dioxide and oxygen be continuously monitored by the gas monitoring system?

• A. Return airway of each ventilation split
• B. Surface control room
• C. Main intake air duct
• D. Goaf area

Answer: (A)

Gas concentration monitoring is aimed at detecting what miners are actually breathing and what could accumulate as air moves from working faces toward the surface. Placing sensors in the return airway of each ventilation split ensures continuous measurement of methane, carbon monoxide, carbon dioxide, and oxygen in the air that has already passed through the mine workings. This location provides timely alarms in the control room so actions can be taken to protect workers, such as adjusting ventilation or evacuating areas, because it reflects the gas levels carried back from the face.

Monitoring the surface control room is important for coordination, but it does not by itself provide continuous in-mine measurements where exposure risks exist. Measuring in the main intake air duct would track fresh air before it interacts with any mine-generated gases, so it wouldn’t accurately represent the gas concentrations miners face. Monitoring in the goaf area can be useful, but concentrations there can be variable and may not consistently indicate the air that is being returned to the surface. The return airway data best represent the actual conditions in the places where miners work and the air they inhale, making it the most reliable continuous monitoring point.