Seng Wah Tan

1. Introduction
Naturally occurring hydrogen free gas receives increasing attentions since naturally occurring H2 could potentially become an important alternative energy source without much carbon footprints unlike hydrocarbons. Natural hydrogen exploration is at its embryo stage attracting attentions of many scientists and explorers. In the current H2 exploration workflow, portable H2 sensors become a de facto tool used to pin down the targets that have H2 emanations. However, despite of it conveniency, it is little known about the reliability of these sensors under the different environmental conditions other than controlled laboratory environment.
The objective of this study is to test the accuracy and reliability of portable gas sensor by conducting a systematic test under laboratory conditions and in the field. The results can help to calibrate the reported hydrogen concentration data and improve the field survey design to obtain more accurate hydrogen concentration data.
2. Methods
Two sites located in a tropic region with ambient temperatures varying between 27 oC and 34 oC were selected for the testing. In each site, 5 shallow boreholes less than 10 m apart each other were drilled with a hand auger. The portable sensors were used to measure the gas composition for these boreholes. Each borehole in the two sites were measured twice which are 14 days apart. During the second measurement, each portable sensors ware put into a thermal box along with 2 ice pads to control the device’s temperature.
3. Results and conclusions
The results showed that this type of electrochemical H2 sensors is sensitive to environmental conditions, especially, temperature. The H2 readings could be affected severely by the environment temperature effect due to the prolonged exposure in the sunlight. Hence, cautions must be taken while trying to link the H2 sensor results with the H2 generation mechanisms during the process of prospecting area screening. Lastly, it is also necessary to re-examine the published H2 data collected with electrochemical sensors before using them to develop any hydrogen generation and migration models.