Ground Gases (CH4, Rn, etc.)
Ground gases are natural gases generated by various processes including material decay (natural and anthropogenic) and magma bodies (adapted from UK HMRC, 2016 and USGS, no date).
Primary reference(s)
UK Government, HMRC, 2016. CIRD61540 - Land Remediation Relief: What is "land in a contaminated state"? Relevant Contaminated Land Remediation: Ground gases. Updated 10 October 2024. Accessed 11 October 2024
USGS, no date. Volcano hazards programme. United States Geological Survey (USGS). Accessed 11 October 2024.
Annotations
Additional scientific description
Chemical or biological processes generate ground gases, for example, the breakdown of uranium-bearing minerals releasing radon from granite or by oxidation and or biogenic reduction (releasing hydrogen sulphide). In addition, naturally occurring ground gases are generated by the biogenic decay of organic matter, for example methane, carbon dioxide and phosphine gas.
The nitrogen cycle produces ammonium (NH+4), nitrous oxide (N2O), nitric oxide (NO) or inorganic nitrogen gas (N2). Nitrous oxide (N2O) levels have risen in the atmosphere as a result of agricultural fertilization (also biomass burning, cattle and feed, and industrial sources).
Landfill gas is a product of the largely biogenic decomposition of anthropogenic waste. Its composition reflects that of the waste, but is dominated by methane and carbon dioxide, becoming more carbon dioxide rich as the waste ages, and with a small amount of non-methane organic compounds. Methane is a potent greenhouse gas (US EPA, no date).
Another source of ground gas associated with continental margins is methane hydrates (Geology.com, 2005-2020). Similarly, ground gases are emitted from volcanogenic sources. Volcanogenic gases escape from magma as a consequence of the pressure relief that occurs as the magma rises to the surface. These gases are also released via geothermal systems and fault systems activated by earthquakes. King et al. (2006) found elevated concentrations of soil gases such as carbon dioxide, helium, hydrogen, mercury vapour and radon in fault zones associated with earthquakes. These gases are released in combination with water vapour and particulate matter during volcanogenic events, or via fumaroles, and hydrothermal systems, as well as faults activated by earthquake events. Earthquakes can also trigger the release of soil gases derived from other sources.
Metrics and numeric limits
No globally agreed limits for ground gases; however, as an example, the UK limits for the following gases are:
- Methane is a colourless, odourless flammable gas. When the concentration of methane in air (oxygen 20.9% by volume [% v/v]) is between the limits of 5% v/v and 15% v/v, an explosive mixture is formed. The Lower Explosive Limit (LEL) of methane is 5% v/v, which is equivalent to 100% LEL. The 15% v/v limit is known as the Upper Explosive Limit (UEL), but concentrations above this level cannot be assumed to represent safe concentrations, because of the potential for dilution to the UEL (NHBC, 2007). Methane is an important greenhouse gas, responsible for around 30% of the rise in global temperatures since the industrial revolution (IEA 2022). Methane has a global warming potential (GWP) of 29.8 ± 11 compared to CO2 (potential of 1) over a 100-year period, and 82.5 ± 25.8 over a 20-year period.
- Carbon dioxide is a colourless, odourless gas, which, although non-flammable, is both a toxic gas and an asphyxiant. As carbon dioxide is denser than air, it will collect in low points and depressions, which can be an extreme hazard during foundation construction and earth movements on development sites. The Long-Term Exposure Limit (LTEL, 8-hour period) and the Short-Term Exposure Limit (STEL, 15-minute period) are 0.5% v/v and 1.5% v/v carbon dioxide, respectively (HSE, no date). The current global average concentration of carbon dioxide in the atmosphere is 425 ppm (March 2024). This is an increase of 50% since the start of the Industrial Revolution.
- Nitrous oxide, also known as laughing gas, it is a colourless non-flammable gas at room temperature. Atmospheric concentration is around 337 parts per billion (ppb) and is a major scavenger of stratospheric ozone, with an impact comparable to that of CFCs. About 40% of anthropogenic emissions are from agriculture.
- Radon is a colourless, odourless radioactive gas derived from the radioactive decay of radium, itself from radioactive decay of uranium. The UK target level for homes is 100 Bq m3 (PHE, no date).
- Levels of hydrogen sulphide of 100 ppm and higher are considered immediately dangerous to life and health (NHBC, 2007).
For further details on metrics and numerical limits please refer to CH00xx Toxic Gases and CH00xx Asphyxiant Gases.
Key relevant UN convention / multilateral treaty
Sendai Framework for Disaster Risk Reduction 2015-2030.
Drivers
Ground gases are generated through natural processes, and can be amplified by anthropogenic activity, such as waste management and agriculture. Volcanoes can produce abundant gas emissions. There are concerns on increasing methane emissions in the arctic linked to the thawing of permafrost.
Impacts
Ground gases are a hazard in terms of risk to human health (see Asphyxiant Gases CH0400 and Toxic Gases CH0300), flammability and climate change (greenhouse gases).
Multi-hazard context
The figure below summarises common interactions between ground gases and other hazards. This information should be used with caution and not be solely relied upon in Disaster Risk Management, particularly as some interactions may not have been included. Note that hazardous events occurring together or locally in space or time may not necessarily cause, amplify, or be otherwise related to each other. Specific examples of multi-hazard context can be found in the ‘Hazard drivers’ and ‘Impacts’ sections above.
Multi-hazard diagram
Risk Management
Where possible, ground gas is monitored and controlled. Where buildings may come into contact with ground gases, specialist construction techniques are deployed to protect human health (e.g., NHBC, 2007). In the case of earthquake- triggered gases, consideration should also be given to the associated particulate matter. Signs in places that are prone to ground gases, for example along hiking trails can warn people of the hazard.
Landfill gas management has been a focal point for national scale reductions in carbon dioxide emissions. For example, in 2018 waste management-related carbon dioxide formed 4.6% of UK carbon dioxide emissions (BEIS, 2020).
Ground gases occur in mining environments, for example in mining for coal (carbon dioxide, methane), potash (methane, nitrogen) and shale gas. In the UK, in these environments, control measures are guided by the Health and Safety Executive.
Readers are referred to Toxic Gases (CH00xx) and Asphyxiant Gases (CH00xx) for further information on drivers, impacts and risk management.
Monitoring
The section and the table below offer an overview of monitoring ground gases. This information can be used for forecasting within a national early warning system (EWS). Since EWS capacities and processes differ across countries, the most current and specific information regarding EWS should be obtained from the appropriate national or regional agency/authority responsible for disaster management.
| Which institution(s) produce(s) Disaster Risk Data/Information? | No Information Available |
| How is the Hazard Observed/Monitored/Forecast? | Oxygen sensors, and similar devices for other gases, fitted with appropriate alarms can detect and warn of developing asphyxiant circumstances. Readers are referred to Toxic Gases (CH0300) for further information on early warning systems for ground gases. |
References
BEIS, 2020. Annex: 2018 UK Greenhouse Gas Emissions, final figures by end user and fuel type. UK Government Department for Business, Energy and Industrial Strategy (BEIS). Accessed 13 February 2025.
Geology.com, 2005-2020. Methane hydrate. Accessed 13 February 2025.
Chataut, G., Bhatta, B., Joshi, D., Subedi, K. and Kafle, K. (2023) ‘Greenhouse gases emission from agricultural soil: A review’, Journal of Agriculture and Food Research, 11, p. 100533. doi: 10.1016/j.jafr.2023.100533.
Health and Safety Executive (HSE), no date. General hazards of Carbon Dioxide. Health and Safety Executive (HSE). Accessed: 13 February 2025
International Volcanic Health Hazard Network (IVHHN), 2020. Health impacts of volcanic gases. International Volcanic Health Hazard Network (IVHHN). Accessed 13 February 2025.
Laurent, M., Fuchs, M., Herbst, T., Runge, A., Liebner, S. and Treat, C.C. (2023) ‘Relationships between greenhouse gas production and landscape position during short-term permafrost thaw under anaerobic conditions in the Lena Delta’, Biogeosciences, 20, pp. 2049–2064. doi: 10.5194/bg-20-2049-2023.
National House Building Council (NHBC), 2007. Guidance on evaluation of development proposals on sites where methane and carbon dioxide are present. National House Building Council. Accessed 13 February 2025.
Public Health England (PHE), no date. What is radon? Public Health England (PHE). Accessed 13 February 2025.
United States Environmental Protection Agency (US EPA), no date. Basic information about landfill gas. United States Environmental Protection Agency.. Accessed 13 February 2025.