Volcanic Gas Hazard Assessment in the Baia di Levante Area (Vulcano Island, Italy) Inferred by Geochemical Investigation of Passive Fluid Degassing

In a volcanic area, the composition of air is influenced by the interaction between fluids generated from many different environments (magmatic, hydrothermal, meteoric, and marine). Any physical and chemical variation in one of these subsystems is able to modify the outgassing dynamic. The increase of natural gas hazard, related to the presence of unhealthy components in air, may depend on temporary changes both in the pressure and chemical gradients that generate transient fluxes of gases and can have many different causes. Sometimes, the content of unhealthy gases approaches unexpected limits, without clear warning. In this case, an altered composition of the air can be only revealed after accurate sampling procedures and laboratory analysis. The investigations presented here are a starting point to response to the demand for a new monitoring program in the touristic area of Baia di Levante at Vulcano Island (Aeolian archipelago, Italy). Three multiparametric geochemical surveys were carried in the touristic area of Baia di Levante at Vulcano Island (Aeolian archipelago, Italy) in 2011, 2014, and 2015. Carbon dioxide (CO2) and hydrogen sulfide (H2S) are the main undesired components, usually present at the local scale. Anomalous CO2 and H2S outputs from soil and submarine bubbling vents were identified; the thermal anomaly of the ground was mapped; atmospheric concentrations of CO2 and H2S were measured in the air 30 cm above the ground surface. Atmospheric concentrations above the suggested limits for the wellbeing of human health were retrieved in open areas where tourists stay and where CO2 can accumulate under absence of wind.

The Rome gas blowout zone (Central Italy)

<p>Colli Albani is an alkali-potassic quiescent volcano of Central Italy that last erupted 36 ka ago. Several lahar generating water overflows have occurred from Albano crater lake, the most recent in Roman times (IV Century B.P.) and the resulting deposits form a surficial impermeable cover on its north-western flank. An important NW-SE trending volcano-tectonic fracture extends from the volcano to the periphery of Rome city. This is a leaky fracture allowing deep magmatic gas to rise toward the surface. In zones where the impervious cover has been removed by excavations, as Cava dei Selci, the gas is freely discharged into the atmosphere creating local hazardous conditions. Elsewhere, the gas dissolves and pressurizes the shallow aquifer confined underneath the impervious cover. Any time this aquifer is reached by a drilling, a dangerous gas blowout may be generated, i.e. a sudden emission of a jet of gas, nebulized water and fine loose fragments of volcanic rocks. Since 2003 four gas blowouts, from ~ 45–50 m deep drillings, have occurred at the boundary between Rome and Ciampino municipalities, a site designed as the Rome gas blowout zone. Dangerous atmospheric CO<sub>2</sub> and H<sub>2</sub>S concentrations killed some animals and several families had to be evacuated because of hazardous gas concentration inside their houses. The emitted gas consists mostly of CO<sub>2</sub> (>90 vol.%) and contains a low but significant quantity of H<sub>2</sub>S (0.3–0.5 vol.%); it has the highest helium isotopic R/Ra value (up to 1.90) of all Colli Albani natural gas discharges. This He isotopic value is similar or even slightly higher than in the fluid inclusions of phenocrysts of the Colli Albani volcanic rocks, suggesting a likely magmatic origin of the gas. Colli Albani volcano is characterized by anomalous uplift, release of magmatic gas and episodic seismic crises. The Rome gas blowouts represent a geochemical window to investigate deep volcanic processes. Should a volcanic unrest occur, gas hazard would increase in this densely inhabited zone, as the input of magmatic gas into the confined aquifer might create overpressure conditions leading to a harmful phreatic explosion, or increase the emission of hazardous gas through newly created fractures.</p>

Gas emissions in volcanic islands: establishing an early warning network for gas hazard management

<p>The La Fossa volcano lies nearby the settled zone of the Island of Vulcano and its last eruption occurred in 1888-1890. Since then, the fumarolic-solfataric degassing accounted for both sulfur and carbon dioxide emissions at Vulcano Porto zone. Long exposure time to CO<sub>2</sub>-polluted air causes severe health injuries, including suffocation. Since volcanic emissions expose people at risk, several international agencies fixed safety threshold figures based on both the gas concentration and the time of exposure.</p><p>This study accounts for the results of the survey performed in the summer of 2020 inside some buildings in the settled zone of Vulcano Porto. The survey aimed at identifying four suitable sites for deployment of continuous surveying stations of both soil CO<sub>2</sub> flux and air CO<sub>2</sub> concentration. This investigation targeted the anomalous soil CO<sub>2</sub> emissions at the Faraglione zone. A comparison between our results and previous studies shows the anomalous degassing zones at Vulcano have not changed their current position substantially. Several significant changes (i.e. independent from changes in atmospheric pressure and temperature) occurred instead in the emissions levels because of the volcanic gas addition. The indoor measurements aimed to verify the conditions where air CO<sub>2</sub> concentration achieves values higher than the safety thresholds, as the results of soil CO<sub>2</sub> flux.</p><p>The investigation targeted several types of environments including both outdoor and indoor sites, either accessed or not by people. The outdoor sites allowed the comparison with air CO<sub>2</sub> levels of the indoor environments. An infrared spectrophotometer enabled the air CO<sub>2</sub> measurements in the range of 0 - 10% vol. At least four measurements were performed at each site with 2 minutes sampling frequency. The results enabled evaluating the CO<sub>2</sub> concentration patterns in a time window consistent with sporadic exposure in the selected sites.</p><p>The results show indoor air CO<sub>2</sub> concentration > 1000 ppm vol in several selected sites. In a few specific sites, the air CO<sub>2</sub> concentration achieved 6% vol after a few minutes of measurement, which is higher than the Immediately Dangerous to Life and Health exposure limit (IDLH = 4% vol). Both the soil CO<sub>2</sub> emissions and air exchange, either normal or artificially induced, caused these air CO<sub>2</sub> values.</p><p>This study shows that gas hazard mitigation includes several actions in the settled zones of Vulcano Porto. The soil CO<sub>2</sub> flux and air CO<sub>2</sub> concentration surveying are both useful actions for risk decrease. However, it is unrealistic to design a network able to identify the risk level above a site-specific threshold and take timely mitigation actions. Comprehensive risk management includes the awareness of the gas hazard among people who live, work or arrive at the island of Vulcano. At the same time, people’s training aims to promote self-reliance in hazard identification and address taking suitable actions against risk in specific cases.</p>

Modelling gas dispersal phenomena at La Soufrière volcano (Guadeloupe, Lesser Antilles)

<p>In recent decades, reliable computational models have significantly advanced, and now represent a valuable tool to make quantitative and testable predictions, supporting gas dispersal forecasting and hazard assessments for public safety. In this study, we carried out a number of tests aimed to validate the modelling of gas dispersal at La Soufrière de Guadeloupe volcano (Lesser Antilles), which has shown quasi-permanent degassing of low-temperature hydrothermal nature since its last magmatic eruption in 1530 AD. In particular, we focused on the distribution of CO<sub>2</sub> and H<sub>2</sub>S discharged from the three main present-day fumarolic sources at the summit, using the MultiGAS measurements of continuous gas concentrations collected during March-April 2017. We implemented the open-source Eulerian code DISGAS-2.0 for passive gas dispersion coupled with the mass consistent Diagnostic Wind Model (DWM), using wind measurements and atmospheric stability information from a local meteorological station and the ECMWF-ERA5 reanalysis data. We found that model outputs are highly dependent on the resolution of the topographic data, which affect mainly the reliability of DWM meteorological fields, especially on and around the steep dome. Our results satisfactory reproduce the observed data, indicating the potential usefulness of DISGAS-2.0 as a tool for quantifying gas hazard and reproducing the fumarolic degassing and at La Soufrière de Guadeloupe.</p><p> </p>

DYNAMICS OF MOTION OF GASES FROM A SOURCE OF SPONTANEOUS COMBUSTION OF COAL IN MINE WORKINGS

The object of this paper is to study the specificity of the dynamics of carbon monoxide in mining to determine the location of the source of coal self-heating or spontaneous combustion. The Fire Dynamics Simulator software package was used to model the gas hazard of coal mine workings. Given the typical details for the western coal basin of Donbas geo metric dimensions of workings, properties of coal, etc., a model of a fragment of emergency mining of a coal mine was created, which allows for the display of geometric and physical similarity to processes in actual mine workings. The results of the simulation for the studied scenarios with different air supply systems related to the detection and location of sources of self-heating or spontaneous combustion in the coal mine workings were obtained and analysed. It was established that low-density fire gases are concentrated in the vault of the workings, where they slowly dissolve in the air, with the dissolution process being linear. It was revealed that air velocity up to 0.67 to 0.7 m/s contributes to the formation of fire gas flows, which move towards the ventilation flow, almost without mixing, which is referred to as bifurcation. Numerical parameters of fire gas dynamics in near-real conditions were established, which can become a basis for the detection and location of sources of endogenous thermodynamic processes in mine workings.

On the issue of determining the main factors of gas hazard in coal mines of Ukraine

The main sources of methane emission are located in the undermined coal-bearing strata, which is not taken into account by the requirements of regulatory documents when determining the category hazard of coal mines. Gas emission from each undermined source is not equally dependent on the tons of coal mined. The relative gas emission changes during the cleaning work and cannot be a criterion for assessing the gas hazard of the entire mine. The volatility of the gas emission index per unit area of the underworked space, which was formed because of monthly movements of the working faces, was established. In essence, this indicator repeats the dependence of the relative gas content per ton of coal mined, since the area of the underworked space is functionally related to the amount of coal mined for a certain period. Without coal mining, the rate of movement of the working face is equal to zero, and gas emission from a unit area continues for several months. As a result, the considered indicators do not have their specific meaning and, due to their inconstancy, they cannot reliably reflect the gas hazard of mines.

Chapter 18 Radon gas hazard

Radon (222Rn) is a natural radioactive gas that occurs in rocks and soils and can only be detected with special equipment. Radon is a major cause of lung cancer. Therefore, early detection is essential. The British Geological Survey and Public Health England have produced a series of maps showing radon affected areas based on underlying geology and indoor radon measurements, which help to identify radon-affected buildings. Many factors influence how much radon accumulates in buildings. Remedial work can be undertaken to reduce its passage into homes and workplaces and new buildings can be built with radon preventative measures.

Chapter 19 Methane gas hazard

This paper identifies potential sources, and the key chemical properties, of methane. Guidance is provided on deriving a conceptual site model for methane, utilizing various lines of evidence to inform a robust, scientific, reasoned and logical assessment of associated gas risk. Discussion is provided regarding the legislative context of permanent gas risk assessment for methane, including via qualitative, semi-quantitative and detailed quantitative (including finite element modelling) techniques. Strategies for mitigating risks associated with methane are also outlined, together with the legal context for consideration of methane both in relation to the planning regime and under Part 2A of the Environmental Protection Act 1990.