And the detector located between the LW face and return airway, what must be tripped?

• A. Electricity supply to LW equipment in the LW face and return airway
• B. Alarm only
• C. The ventilation shaft
• D. The ambient lighting

Answer: (A)

The key idea is that gas detectors in a longwall setting are tied to automatic safety shutdowns to remove ignition sources when gas levels rise. A detector placed between the longwall face and the return airway is positioned to sense methane (or other flammable gas) ahead of the return so that, if a dangerous concentration is detected, the system immediately cuts power to the longwall equipment in that face area. This cold-fire prevention—disconnecting electricity to LW equipment—helps prevent ignition and potential explosions as gas migrates toward the return air.

So the correct action is to trip the electricity supply to longwall equipment in the longwall face and return airway, stopping equipment that could ignite gas. An alarm by itself warns but does not remove the ignition source. Tripping the ventilation shaft or ambient lighting is not the function of this detector in that location; they serve different roles in ventilation control and visibility, not direct ignition protection.