Gas hazard related to CO2 degassing at Loutra Ypatis, Greece

Abstract

Earthquakes and volcanic eruptions represent a hazard. However, the impact of gases released in geodynamically active areas should not be underestimated. It is commonly known that geogenic sources release great amounts of gases, which, apart from having an important influence on the global climate, can also have a strong impact on human health causing both acute and chronic effects. In particular, CO2 and sulphur gases (mainly H2S and SO2) are the main compounds responsible for acute mortality due to their asphyxiating and/or toxic properties. One of the most known and also worst episodes occurred, took place on the 21th of August 1986 at Lake Nyos, Cameroon, when about 1700 people were killed and 850 injured by a massive CO2 release (D’Alessandro, 2006). Like other geodynamically active areas, Greece is also affected by a large number of geogenic gas manifestations (Daskalopoulou et al., 2018a). These occur either in the form of point sources (fumaroles, mofettes, bubbling gases) or of diffuse soil gas emanations (Daskalopoulou et al., 2018b). D’Alessandro and Kyriakopoulos (2013) made a preliminary estimation of the risk related to geogenic gases in Greece for the time period of 1992-2011; the whole population of the country was considered. In that period, at least two fatal episodes with a total of three victims took place, likely caused to the exposure to geogenic gases (specifically CO2). This would give a risk of 1.310-8 fatality from geogenic gas manifestations per annum. This value, although probably underestimated, is much lower than many other natural or anthropogenic risks. Since deaths due to natural gases are often wrongly attributed, it cannot be excluded that some fatal episode has not been recognized and thus that the risk is somewhat higher than assessed. Although very low, this risk should not be neglected, not only because it is possibly underestimated, but also because simple countermeasures could be adopted for risk reduction. Dangerous areas could be easily identified and delimited by geochemical prospecting and their hazards properly highlighted. Apart from the sites where fatal episodes occurred, many other hazardous sites have been recognized in Greece. Here we present data collected at Loutra Ypatis (central Greece). Study area Sperchios Basin – Evoikos Gulf Graben is a 130 km long actively spreading graben in Central Greece (1 cm/a). The high geothermal gradient of the area is evident by the presence of many thermal springs with temperatures that vary from 24 to 82 °C. In the waters of these springs, discharging along the normal faults bordering the graben, an abundant gas phase is bubbling. Loutra Ypatis is one of the emerging springs and its waters (31 °C) are exploited by a spa. The water is currently drained by a gallery and therefore the water level is about 5 m below ground at the bottom of a funnel-like hole (Fig. 1 left). For safety reasons the hole was covered by a closed building (Fig. 1 left and center). The gas, which is vigorously bubbling in the spring, is mostly (> 96%) composed of CO2 (D’Alessandro et al., 2014). The walls of the hole are covered of sulfur that derives from the partial oxidation of the H2S (2500 ppm) contained in the released gas (D’Alessandro et al., 2014). Methods In October 2015 atmospheric concentrations of CO2 were measured with a Licor LI820 NDIR spectrometer (range 0 to 20,000 ppm, accuracy of 2%), whilst in April 2016, the atmospheric concentrations of CO2 and H2S were measured with a Multi-GAS analyser manufactured by INGV-Palermo equipped with Licor LI-840 NDIR spectrometer (CO2 0-20,000 ppm) and an EZ3H electrochemical sensor by City Technology Ltd. (H2S 0–100 ppm). Simultaneous CO2, CH4 (both 0- 100%), CO, H2S (both 0-500 ppm) and O2 (0 – 25%) concentrations within the building were measured with a portable gas analyser GA2000 (Geotechnical Instruments). Results and discussion Due to the fact that a bui