30 June 2015
BSI, the business standards company, has revised BS 8485 Code of practice for the design of protective measures for methane and carbon dioxide ground gases for new buildings. The standard is a key piece of guidance for consultants for the design of investigations and gas protection measures for new developments, and regulators (environmental health officers and building control) who need to assess/approve foundation designs. This is the revision and retitling of BS 8485 which now references and reflects several British Standards and industry good practice guidance published since its publication in 2007.
When building or developing on or adjacent to brownfield sites, where degradable materials are present within the ground, and in areas of mineworkings, there is a potential risk of the generation of ground gases and accumulation of these gases within buildings. Toxic, asphyxiating and explosive ground gases (methane and carbon dioxide) can enter buildings and other structures on and below the ground. They pose potential risks to occupants and users, and to the structures themselves such as a potential risk of explosion or asphyxiation.
BS 8485 recognizes that there are a number of factors which can affect the sensitivity of a development to the effects of ground gas, and that there is a range of design solutions available for different situations. It is anticipated that specialist advice is required in the assessment of ground gas data and in the risk assessment phase. BS 8485 provides a framework, in line with Model procedures for the management of land contamination, CLR 11 which guides designers about what is required for an adequate ground gas site investigation.
BS 8485 gives recommendations on ground gas site characterization and the choice of solutions for the design of integral protective measures for new buildings to prevent entry of carbon dioxide and methane, and provide a safe internal environment. It helps to identify the risks posed by the potential or actual presence of carbon dioxide and methane, and that they have been addressed.
Key changes to BS 8485:
- Clearer guidance on the interpretation of gas monitoring data and assignment of characteristic situations (CS)
- Reference Technical Note RB17 CS classification using TOC (toxic organic compounds)
- Review and expanded guidance on protection measures scoring (old Table 3)
- Include reporting requirements
- Added annexes on radon and volatile organic compounds (VOC's)
- More detailed guidance on interpretation of gas monitoring data
David Fatscher, Head of Market Development for Sustainability at BSI, said: “BS 8485 goes a long way towards clarifying what land developers, designers and regulators need to know when considering the status of the ground. This guidance is not prescriptive and professional judgement should be made as to the acceptability of risk, as to whether a more rigorous site assessment or adoption of conservative measures in design need to be adopted.”
BS 8485 was developed using collaborative input from experts within the construction industry, environmental and geotechnical engineering, environmental health, building control officers, as well as environmental and private consultants.
Richard Owen, Committee Chair for BS 8485 said: “This substantially expanded (and re-named) second edition of BS 8485 reflects the considerable advances in industry guidance, practice and experience for protection of new buildings against methane and carbon dioxide ground gases since the Standard’s first publication in 2007. It cross references BS 8576:2013 for guidance on ground gas investigation and includes much more detailed guidance on the interpretation of gas monitoring data, including worked examples. Four building ‘types’ and definitive requirements for membranes to be assigned gas protection points are described for the empirical method presented in the standard. I am sure that designers of gas protection measures and regulators involved in the assessment of design solutions will find this updated and expanded second edition a key reference.”