UK is facing a rising problem from harmful, naturally occurring ground gases and vapours. To protect both the structure and its users, it is crucial that ground gases are identified and managed.
The presence of gases on a site may be due to its natural, or historical use.
The naturally occurring gases methane is carbon dioxide, nitrogen, and radon. However, these gases can also be found in soil in elevated concentrations relative with normal atmospheric gasses.
Sites that were previously used as a landfill or heavy industrial use or where petrol, oils or solvents might have been spilled can also produce hazardous gases like methane, carbon dioxide and volatile organic compounds (VOCs), such as benzene, and trace gas components, such as hydrogen sulfuride and carbon monoxide.
The above gases and vapours all have a variety of properties, such as being asphyxiating, flammable, potentially explosive and others are highly toxic and over several decades of low exposure can cause cancer. Some of them may chemically interact and affect concrete and plastic materials, thereby affecting the structural integrity. They can also enter buildings and other structures below ground level.
These are the different types of gases
- Radon
- Carbon Dioxide
- Nitrogen
- Methane
- Hydrogen
- Sulphide
- Volatile organic compounds (VOC)
Radon, carbon dioxide and methane gasses, as well as VOCs (Volatile Organic compounds such as hydrocarbons), pose a danger to your health. Therefore, new constructions must use the appropriate materials to keep them out.
An independent ‘Gas protector verification plan’ is required in accordance with CIRIA C735. For gas protection, it is necessary to follow a robust design process and construct the building. After the construction has been verified, it is time to prepare handover documentation. This document should outline any additional measures that may be required, such as those necessary for preventing damage or during operation and maintenance.
It is strongly recommended that specialists be consulted during the assessment of groundgas data as well as the risk assessment phase. Here are some key documents that you should be aware of.
- 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
BS8485:2015 + A1 2019 provides recommendations on ground gas site characterisation and the choice of solutions for the design of integral gas protective measures for new buildings to prevent the entry of carbon dioxide and methane and provide a safe internal environment. It provides a way to demonstrate that potential or actual carbon dioxide and methane risks have been mitigated.
To ensure the installation of your gas protection systems meets the required legislation & regulations please contact our Edinburgh team
How does ground gas occur?
Why is ground gas becoming a problem?
In the past, ground gases were not perceived as a risk to the users or the buildings. As it is becoming increasingly difficult to find suitable sites for development, there has been an increase in the number of brownfield sites. Brownfield sites can have pollutants that affect the soil and ground.
Because of this increased awareness, the Environment Agency developed new legislation that addresses potential ground gas problems.
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.
Assessment of ground gas risks
At the desk stage, ground gas and vapour risks are assessed. Ground investigation or assessment is then done. If ground gas hazards are discovered, measurement with monitoring wells in boreholes will usually be part of the investigations. Existing buildings can be monitored using static measurement methods and diffusion tubes. The nature of the risk can affect the length of monitoring programs. They may last for days or even months.
After the investigation is complete, an interpretation of the measurement data can be used to determine whether ground gases or vapours are at risk.
Protection from below ground gases
Ground gas protection is an extremely specialised operation. GeoShields Ground Gas specialists have the required knowledge, experience and skill levels.
Mitigation of the harmful ground gases is usually provided by the use of ventilation and ground gas membranes during construction design, which provides both primary and secondary forms of protection for buildings from the ingress of gases and vapours. A foundation-based ground gas protection system is unlikely to be practical if you’re already a homeowner. Therefore ventilation is the key. You can mix natural ventilation for suspended floors with improved underfloor ventilation or introduce mechanical ventilation systems to control the ground gases and vent them away from your property. In every case, validation of the construction methods and their installation is necessary.
In some cases where the risks posed by gases and vapours are due to them being a by-product of more significant soil or groundwater contamination, mitigation can be provided by the remediation of the specific contamination sources.
What impact could it have on your life if you do 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. There have been studies that radon may cause lung cancer. Carbon Dioxide is toxic and can cause asphyxiation. Methane or volatile organic compounds can also be explosive and flammable. Methane can be flammable at levels as low as 5%
The property may be deemed too dangerous for mortgage lenders.
What is Ground Gas Membrane?
Because of the danger posed by ground gases, buildings must be protected in order to protect the structure and prevent injury to anyone who is inside. Protection is usually in the for of a ground gas membrane.
Ground gas protection materials are made mainly from polymers, however they can also include other materials like aluminium. They are lightweight, flexible, and easily formable. They can stop gas from getting into buildings and the ground.
To ensure the installation of your gas protection systems meets the required legislation & regulations please contact our Edinburgh team
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