UK is experiencing a growing concern about harmful, naturally occurring underground gases and vapours. It is essential that ground gases and their risks are recognised and minimised in order to protect the structure.
A site could have natural gasses, or they may be the result of an historical use.
There are many naturally occurring gases, including methane (carbon dioxide), nitrogen, and radon, and they can all be found in the soil in higher concentrations than those of normal atmospheric gases.
Sites with a history of heavy industrial use, landfills, or spillage of petrol, oil, or solvents can produce dangerous gases such methane and carbon dioxide.
Each of the gases and vapours mentioned above have different properties. Some are asphyxiating, flammable and potentially explosive. Others can be toxic and, over many decades, can cause cancer. They can also react chemically with concrete and plastic building materials, which could affect the structural integrity of the buildings. They can be found in buildings and other structures above and below ground.
These are the different types of gases
- Radon
- Carbon Dioxide
- Nitrogen
- Methane
- Hydrogen
- Sulphide
- Volatile organic compounds (VOC)
Gases such as Radon, carbon dioxide, methane and VOCs (Volatile Organic Compounds such as hydrocarbons) are a risk to health and therefore new constructions must use appropriate materials to keep these gases out of the structure and they must be installed following the recommended guidelines.
Conforming to CIRIA C735, a independent ‘Gas protective verification plan’ must be prepared. A robust design and construction process should then be followed to install the gas protection measures and the requirements of ‘verification plan’ implemented. After construction passes independent verification, handover documentation should then be prepared. It should detail any steps required during the construction process to prevent damage as well as for the operation and maintenance of the building.
It is a good idea to seek specialist advice during the evaluation of the groundgas data and during the risk assessment phase. Below are some important documents to keep in mind and reference:
- BS 8485:2015+A1:2019 - Codes of practice for the design of protective measures for methane and carbon dioxide ground gases for new buildings.
- CIRIA C748:2014 - Guidance on the use of plastic membranes as VOC vapour barriers
- CIRIA C682:2009 - VOC Handbook
- CIRIA C735:2014 - Good practice on testing and verification of protection systems to buildings from hazardous gases
- BS 8102:2009 - Code of practice for protection of below ground structures against water from the ground
BS8485+A1 2019 offers recommendations on ground-gas site characterisation and the selections of solutions to design integral gas protective mechanisms for new buildings. This is done in order to prevent methane and carbon dioxide from entering and maintain a safe interior environment. It provides a way to demonstrate that potential or actual carbon dioxide and methane risks have been mitigated.
Contact our Birmingham team today to book your gas protection systems verification inspection
How does ground-gas occur?
What has happened to ground gas?
Ground gases weren’t considered to be a threat to buildings and users in the past. The demand for new homes has also led to an increase in development on brownfield sites (formerly developed sites), as it has become more difficult to find new sites to develop. However, brownfield sites can contain soil and ground pollutants.
Due to the the increased awareness of the risks the Environment Agency has produced new legislation with a much stricter approach when dealing with potential ground gas issues.This legislation has been adopted by local authorities throughout the country.
It is important that you note that possible risk factors cannot be determined without a detailed ground gas investigation by a qualified ground gas surveyor.
Ground gas risk assessment
The potential for a risk from ground gases and vapours is firstly assessed at desk stage, with ground investigation or assessment designed accordingly if risks of ground gases are identified then measurement using monitoring wells in boreholes will normally be used as part of the investigations. You can use static measurement techniques and diffusion tubes in buildings. Monitoring programmes can range from days to months depending on the nature of the risk.
Once the investigation has been completed, the analysis and interpretation of measurement data will reveal whether there are ground gases or vapours.
Protection from below-ground gasses
Ground gas protection can be a complex operation. GeoShields Ground Gas Specialists have the necessary knowledge, experience, and skills.
Ventilation and ground gas membranes are used to mitigate the effects of harmful ground gases. They provide both primary and secondary protection for buildings against the ingress and vapours. If you are already a homeowner living in a property then foundation based ground gas protection will most likely be impractical. Ventilation is essential. The best ventilation is a combination natural ventilation for suspended floors, underfloor ventilation, and mechanical ventilation systems. This will allow harmful ground gases to be safely controlled and vented from the property. In all cases validation of the construction and the installation techniques is important.
There are some situations where gases and vapours may pose risks because they are a byproduct of soil or groundwater contamination. This can be mitigated by remediating the source of contamination.
What could be the effect of doing nothing?
The impact of not reacting when ground gas is discovered depends on what type of ground gas was found. Some gas will cause health problems while others will damage the building’s integrity. It has been found that the effects of radon on the human body can cause lung cancer, Carbon Dioxide can be toxic and cause asphyxiation, Methane and Volatile organic compounds (VOC) can be explosive/ flammable. Low levels of Methane (5%) can make it flammable.
Mortgage lenders might also consider your property to be too risky, which could have negative consequences for your health and increase the chance of fire.
What is Ground Gas Membrane and How Does It Work?
Buildings must be protected due to the dangerous nature of ground gases. Protection can be found in the form of a ground-gas membrane.
Ground gas protection membranes are typically made from polymers, but can also be made with other materials like aluminium. These membranes are light, flexible and formable thanks to their flexibility. They prevent gas from flowing into the building from the ground.
Contact our Birmingham team today to book your gas protection systems verification inspection
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