How many sensors are enough for an underground coal mine refuge?

4 sensors. After checking the information about coal mine wells, we know that 4 sensors are enough for a coal mine underground refuge. The wells in a coal mine are called vertical shafts. The main vertical shaft and the secondary vertical shaft are the two main shafts (shaft mines) of a coal mine, and the main vertical shaft is mainly used for the transportation of large equipment and materials and the export of mined coal.