THE EVALUATION OF HYDROGEN DETECTORS FOR USE IN COAL-MINES

Hydrogen detection at low levels (0-200 ppm) in coal mines provides useful confirmatory evidence of a self-heating process. At the high levels (0-2%) that can occur after a methane explosion, hydrogen detection is essential for determining the presence of potentially explosive mine atmospheres. Hydrogen detectors of various types were evaluated to determine their suitability for use in coal mine environments; measurements were made of their response to hydrogen and their cross-sensitivity to other gases normally present in mine atmospheres. The effects of variations of temperature and humidity on the response to hydrogen were also evaluated. Two homogeneous semi-conducting sensors based on tin dioxide were found suitable for selective hydrogen detection in a heat-up situation (0-200 ppm). A multi-sensor system for the early and unambiguous indication of spontaneous heat-up was developed. No detector was found for the selective monitoring of hydrogen at the percentage level.