Fiber Optic Methane Sensor for Mines

Lower level of methane detection between 0-5 % is very important in underground coal mines for safe and fearless operation as methane-air mixture is highly explosive between 5-14.5 %. At present catalytic combustion type methane sensors are being used for the routine monitoring of methane gas between 0-5 % which is an electrically heated pellister. Optical interferometer type methane sensor is also being used for detecting 0-10 % of methane. Thermal conductivity type methane sensor is used for detecting methane percentage between 0-100%. Recently fibre optic methane sensor has been reported in the literature and the authors have also explored the attractive feature of intrinsic safety of fibre optic sensors for mines. In this paper different techniques based on evanescent wave spectroscopy method of detection of methane gas have been discussed. Cladding removal with evanescent wave modulation, sol-gel cladding and evanescent field detection of methane gas using D-fiber have been described. Merits and demerits of each technique have been highlighted. Optical fiber, being a dielectric, non-metallic and non-sparking, is an intrinsically safe media and is ideally suited to the hazardous environment present in mines.