Where must the AFC detector be installed and what are its functions?

• A. On each electrically-powered tailgate drive motor; alarm at 1% and trip the electricity supply to the AFC and the longwall shearer cutters when the concentration exceeds 2%.
• B. On the main exhaust fan with alarm at 3% and trip at 4% only.
• C. On the belt conveyor with alarm at 5% and trip at 6% only.
• D. Inside the control room with an audible alarm only.

Answer: (A)

The test focuses on placing AFC methane detectors to protect against gas hazards by both warning and stopping equipment at the source. The detector should be on each electrically powered tailgate drive motor because that location monitors gas where it could cause ignition right at the face, before it spreads. When methane is detected at a low level (1%), an alarm sounds to warn personnel; if it climbs to a higher level (2%), the system automatically trips the power to the AFC and the longwall shearer cutters, stopping potential ignition sources and reducing the risk of an explosion.

Placing detectors on the main exhaust fan would only monitor ventilation performance, not provide immediate protection to the face equipment; on a belt conveyor similarly doesn’t address the critical ignition risk at the AFC area. A detector inside the control room with only an audible alarm would rely on someone to react and would not automatically remove the hazard.