Methane and other site gasses from the ground
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, gasses 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 gasses 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 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.
 Related articles on Designing Buildings Wiki
- 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.
- Pre construction information.
- Radon: Guidance on protective measures for new buildings BR 211.
- Site appraisal.
- Site information.
- Soil survey.
- Solid and liquid contaminants risk assessments.
Featured articles and news
ICE 200 brings together transformative projects from the past 200 years - and the engineers behind them.
Dame Judith Hackitt hosts an industry summit to kick start the second phase of the review.
This article explains the Buildings Regulations completion certificate, what it is, and when its needed.
Graphene has many potential applications, but when will it start being used in civil engineering?
Increasing productivity – now more than ever as we lead up to Brexit – should be the sector’s number one priority in 2018.
Carillion's collapse causes Construction Leadership Council to delay the construction sector deal report.
Urban Heritage, Development and Sustainability: international frameworks, national and local guidance.
What will the General Data Protection Regulations (GDPR) mean for you when they come into force in May?
Business Secretary chairs a new taskforce to monitor and advise on mitigating the impacts of Carillion’s liquidation.
Sir John Armitt is appointed the new chair of the National Infrastructure Commission.
High quality and high density homes - is it what we need or is it storing up trouble?
Government announces its intention to strengthen planning rules to protect music venues and neighbours.