Fiber optics for atmospheric mine monitoring

The authors describe work done to address methane, carbon monoxide, and distributed temperature monitoring. A review is made of the potential and problems of using fiber optics (FOs) 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 FO cable is described. A carbon monoxide monitoring system that combines a low-powered electrochemical cell with fiber optic (FO) telemetry is described. Testing has shown that the system can operate maintenance free for several months. A distributed FO temperature-monitoring system is being investigated for possible application in mine fire detection. Performance of this system at the US Bureau of Mines´ Lake Lynn Laboratory is reported. 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. Distributed temperature sensors have considerable potential for monitoring areas such as conveyor beltways