What action occurs when CH4 GB concentration in the return air exceeds 2%?

• A. The detector triggers a visible alarm only.
• B. The electricity supply to the AFC, shearer cutters and Longwall equipment in the return airway is tripped.
• C. The detector activates the ventilation system's exhaust.
• D. The detector locks out the area and requires manual reset.

Answer: (B)

When methane in the return air reaches that level, the safety design automatically cuts the power to ignition sources in the return airway. The essential action is to trip the electricity supply to the major equipment on the longwall face—such as the AFC, shearer cutters, and other longwall gear—so that no sparks or heat from running machinery can ignite the methane.

This is why the option that trips power is the best fit: it directly removes the energy sources capable of ignition in a methane-rich environment, reducing the risk of an explosion. Merely sounding a visible alarm doesn’t stop equipment, and delaying action by relying on ventilation changes or a manual lockout could leave a dangerous window where ignition is possible.