FIBER OPTICS FOR ATMOSPHERIC MINE MONITORING

Fiber optic (FO) technology is progressing rapidly, including the development of FO sensors for a wide variety of applications. These sensors have the advantage of high sensitivity, light weight, small size, high bandwidth, and freedom from electromagnetic influences. The U.S. Bureau of Mines is investigating the application of FO technology to monitoring mine atmospheres. This paper describes work done to address methane, carbon monoxide, and distributed temperature monitoring. A review is made of the potential and problems of using FO's 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. The upper range is 100% volume methane. Since the system requires no electrical power within the mine, it is intrinsically safe. A carbon monoxide monitoring system that combines a tow-powered electrochemical cell with FO telemetry is described. Testing has shown that the system can operate maintenance free for several months. Finally, a distributed FO temperature-monitoring system is being investigated for possible application in mine fire detection. Performance of this system at the Bureau's 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.