UK residents are facing increasing problems from dangerous, naturally occurring below-ground gasses and vapours. It is essential that ground gases and their risks are recognised and minimised in order to protect the structure.
There are two possible sources of gas that could be present on a site: they can be natural or they can be a result from its history.
Methane, carbon dioxide and nitrogen are all naturally occurring gases. Many of these gases can be found in soil at higher concentrations than normal atmospheric gases.
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.
All of the above gases and vapours can have a variety properties such as being toxic, asphyxiating and flammable. They can also react chemically with concrete and plastic building materials, which could affect the structural integrity of the buildings. They can penetrate buildings and other structures both above and below the ground.
These are the different types of gases
- Radon
- Carbon Dioxide
- Nitrogen
- Methane
- Hydrogen
- Sulphide
- Volatile organic compounds (VOC)
Radon, carbon dioxide methane, methane, and VOCs (Volatile Organic Chemical Compounds such hydrocarbons) pose a threat to human health. New constructions must contain the right materials to prevent these gases from entering the structure. They must also be installed according to the recommended guidelines.
According to CIRIA C735, a separate ‘Gas safety verification plan’ (or ‘Gas protection verification document’) is required. A robust design and construction process should then be followed to install the gas protection measures and the requirements of ‘verification plan’ implemented. Once construction passes the independent verification, you should prepare handover documents. These should list any requirements during the remaining phases of construction, including to prevent damage or maintain the building.
Specialist advice is highly recommended during the assessment and risk assessment phases of ground gas data. 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+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 method that can be used for demonstrating that there are no risks from the possible or actual presence carbon dioxide and methane.
To ensure the installation of your gas protection systems meets CIRIA 735 & BS8485 please contact our Cardiff team
How does ground gas occur?
Why is ground gas becoming a problem?
In the past ground gases where not perceived as a risk to users and the buildings themselves. Also the requirement for more new homes has led to the increase of development on previously developed sites, (Brownfield sites) as finding new sites to develop on has become increasingly difficult. Brownfield sites may contain contaminants that can affect the ground or soil.
The Environment Agency’s increased awareness of potential risks has led to new legislation being adopted by local authorities in all parts of the country.
It is important to keep in mind that potential risks can only be identified through an extensive ground gas investigation conducted by a qualified ground gas surveyor.
Ground gas risk assessment
The risk from ground gases or vapours must be assessed first at the desk stage. If ground gas risks are identified, then borehole measurement will be performed. In existing buildings, diffusion tubes or other static measurement techniques may be used. The risk nature can impact the duration of monitoring programs.
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 gases
Ground gas protection requires a high level of expertise. The GeoShields Ground Gas experts have the knowledge, experience, and skill to do it.
Ground gas protection is often achieved by ventilation and ground membranes in construction. This provides primary and secondary protection against the ingress of gases. If you are already a homeowner living in a property then foundation based ground gas protection will most likely be impractical. 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.
Sometimes, the gas and vapours can pose a risk because they are a result of soil or groundwater contamination. In these cases, remediation may be possible.
What could be the effect of doing nothing?
It is up to you to decide whether or not you react to the discovery of possible ground gas risks. Some will impact your health, while others could affect the integrity and safety of the building. 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. Methane can be flammable at levels as low as 5%
You may find that the property is too risky for mortgage lenders.
What is Ground Gas Membrane, exactly?
Ground gases are dangerous and buildings need to be protected. This protects the structure’s integrity as well as anyone inside it. Protection is usually in the for of a ground gas membrane.
Ground gas protection membranes are usually constructed from polymers but also include other materials such as aluminium. This allows them to be lightweight, flexible and formable. They prevent gas from flowing into the building from the ground.
To ensure the installation of your gas protection systems meets CIRIA 735 & BS8485 please contact our Cardiff team