Ground gas
The term ‘ground gas’ refers to gases such as carbon dioxide and methane, which are generated within the ground and/or within landfills, commonly from the breakdown of vegetative matter. Ref The HS2 London-West Midlands Environmental Statement, Glossary of terms and list of abbreviations, DETR 2013.
Approved document C, Site preparation and resistance to contaminants and moisture, suggests that ‘methane and other gases’ includes hazardous soil gases (other than radon, which is dealt with separately), which originate from waste deposited in landfill or are generated naturally.
They may include gases such as methane, carbon dioxide, volatile organic compounds (VOCs) and nitrogen which can migrate through the subsoil and through cracks and fissures into buildings, where if they build up to hazardous levels, cause harm to health or compromise safety:
- Methane is an explosive and asphyxiating gas.
- Carbon dioxide is toxic.
- VOCs are flammable and toxic and can have an unpleasant odour.
They may be apparent as:
- Landfill gas, produced by the action of micro-organisms on biodegradable waste materials, including; methane, carbon dioxide and small quantities of VOCs.
- Elevated levels of carbon dioxide and nitrogen, occurring naturally in coal-mining areas
- Methane and carbon dioxide occurring in organic rich soils and sediments such as peat and river silts.
- VOCs occurring as a result of petrol, oil or solvent spillages.
The assessment of the risk from ground gases should adopt a tiered approach. A preliminary risk assessment should be undertaken, and depending on the outcome, either a generic quantitative risk assessment (GQRA) or detailed quantitative risk assessment (DQRA), or both, may be necessary.
Where risks are unacceptable then these need to be managed through appropriate building remedial measures or site-wide gas control measures, such as the removal of the gas generating material or 'covering' (placing one or more layers of materials over the site) together and the use of gas extraction systems.
Control measures for dwellings may include gas resistant barriers above an extraction or ventilation layer from which gases can be passively dispersed and vented to the atmosphere.
Control measures for non-domestic buildings, which may have a larger footprint, may require mechanical dispersal and ventilation systems, monitoring and alarms. These systems will require ongoing maintenance and calibration.
[edit] Related articles on Designing Buildings
- Brownfield land.
- Building on fill.
- Contaminated land.
- Cover systems for land regeneration - thickness of cover systems for contaminated land (BR465).
- Deleterious materials.
- Designing to reduce the chemical, biological and radiological vulnerability of new buildings (IP 7/15).
- Ground conditions.
- Landfill tax.
- Methane.
- Natural gas.
- Pollution.
- Pre construction information.
- Radon.
- Radon: Guidance on protective measures for new buildings BR 211.
- Radon protection for new domestic extensions and conservatories with solid concrete ground floors (GG 73 revised).
- Radon protection for new large buildings GG 75.
- Radon protection for new dwellings GG 74.
- Radon solutions in older homes GR 38.
- Site appraisal.
- Site information.
- Solid and liquid contaminants risk assessments.
- Synthetic methane.
Featured articles and news
HSE simplified advice for installers of stone worktops
After company fined for repeatedly failing to protect workers.
Co-located with 10th year of UK Construction Week.
How orchards can influence planning and development.
Time for knapping, no time for napping
Decorative split stone square patterns in facades.
A practical guide to the use of flint in design and architecture.
Designing for neurodiversity: driving change for the better
Accessible inclusive design translated into reality.
RIBA detailed response to Grenfell Inquiry Phase 2 report
Briefing notes following its initial 4 September response.
Approved Document B: Fire Safety from March
Current and future changes with historical documentation.
A New Year, a new look for BSRIA
As phase 1 of the BSRIA Living Laboratory is completed.
A must-attend event for the architecture industry.
Caroline Gumble to step down as CIOB CEO in 2025
After transformative tenure take on a leadership role within the engineering sector.
RIDDOR and the provisional statistics for 2023 / 2024
Work related deaths; over 50 percent from construction and 50 percent recorded as fall from height.
Solar PV company fined for health and safety failure
Work at height not properly planned and failure to take suitable steps to prevent a fall.
The term value when assessing the viability of developments
Consultation on the compulsory purchase process, compensation reforms and potential removal of hope value.
Trees are part of the history of how places have developed.