Longwall return detectors must be located at what distance outbye from the corner of the tailgate block side rib line and the longwall coal face?

• A. 50 m
• B. 100 m
• C. 150 m
• D. 200 m

Answer: (C)

Detector placement for longwall return is about ensuring timely smoke detection in the return air path. In a longwall setup, air moves from intake across the face and then back through the tailgate toward the return airway. Positioning the detector outbye from the corner where the tailgate block side rib line meets the longwall coal face places it in the main return stream, so it can sense smoke early as it travels away from the face and toward safety controls.

The 150 m distance is chosen as a practical balance: close enough to provide early warning and time to react, but far enough to sample a representative portion of the return air and avoid being overwhelmed by near-face disturbances. Placing detectors much closer (like 50 m or 100 m) could miss portions of the return air path or be more prone to false alarms from dust near the face, while placing them much farther (such as 200 m) could delay detection and reduce reaction time.