Fiber optics for atmospheric mine monitoring

The authors describe work done by the US Bureau of Mines to address methane, carbon monoxide, and distributed temperature monitoring. A review is made of the potential and problems of using fiber optics for mine monitoring systems. Methane detection is based on differential absorption of infrared light. A methane monitor that can detect concentrations as low as 0.2% as far away as 2 km via fiber-optic cable is described. The upper range is 100% volume methane. Since the system requires no electrical power within the mines, it is intrinsically safe. A carbon monoxide monitoring system that combines a low-powdered electrochemical cell with fiber-optic telemetry is described. Testing has shown the system can operate maintenance-free for several months. Finally, a distributed fiber-optic temperature monitoring system is being investigated for possible application in mine fire detection. The sensor employs optical time domain reflectometry techniques that allow the entire length of fiber (up to 2 km) to function as a distributed temperature sensor.<<ETX>>