Influences of Oxygen Concentration on the Determination of Methane Associated with Hot Springs, with a Catalytic Combustion Gas Detector and a Gas Chromatograph

Abstract

In order to prevent disasters of the explosive accidents involving methane gas associated with hot springs in Hyogo Prefecture, we examined the analysis methods of the methane, and investigated the distribution of methane in the Prefecture. We examined the analysis methods of methane by combustible gas detectors on-site and gas chromatography (GC) at a laboratory. In this study, a catalytic combustion detector was used. Results obtained from the detector method and from the GC method were compared. While measuring by a detector, when the oxygen concentration was insufficient, the deviation from the set level and the measured level was significant. However, our study revealed that by supplying oxygen through an air suction port on the detector, the influence of a low oxygen concentration could greatly be decreased. On the other hand, a measurement by the GC method was not influenced by the oxygen concentration. Methane gas levels at 104 hot spring sources in Hyogo prefecture were measured by a method combining the use of a detector and GC. The results showed that the concentration of methane was in the range between N.D. and 1560%LEL (78vol%), while the oxygen concentration was in the range from 0.01% to 17.0%. Furthermore, at 21% of the targeted hot spring sources, the methane gas concentration was found to be in excess of the standard level.