UK is experiencing a growing concern about harmful, naturally occurring underground gases and vapours. To protect the structure as well as its users, it is important to assess the risk of ground gasses and how they can be mitigated.
Gases that may be present on a site can be naturally occurring or they may be as a result of its 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 whose previous use was as a landfill, heavy industrial use, or where petrol, oil or solvents may have spilled can also generate hazardous gases such as methane, carbon dioxide, volatile organic compounds (VOCs) such as benzene and trace gas components such as hydrogen sulphide and carbon monoxide.
These gases and vapours have many properties. They can be asphyxiating or flammable, explosive, potentially explosive, and other toxic. Low exposure for several decades can lead to cancer. They can also react chemically with concrete and plastic building materials, which could affect the structural integrity of the buildings. They can get into buildings and other structures at 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.
A ‘Gas Protection Verification Plan’ independent of CIRIA C735 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. 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.
Specialist advice is highly recommended during the assessment and risk assessment phases of ground gas data. These are the most important documents you need to know and to refer to:
- 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 gives recommendations on ground gas site analysis and the selection and implementation of gas protection measures to protect new buildings from carbon dioxide and methane. 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 call our Sunderland team
How does ground gas happen?
Why has ground gas become such a problem
Ground gases weren’t considered to be a threat to buildings and users in the past. Due to increasing demand for homes, brownfield sites have seen an increase in development. This is because it is more difficult to find new land to develop. However, brownfield sites can contain soil and ground pollutants.
Because of this increased awareness, the Environment Agency developed new legislation that addresses potential ground gas problems.
It is important for you to know that potential risk factors can only been determined by an in-depth ground gas investigation. This must be done by a competent ground gas surveyor.
Assessment of ground gas risk
First, assess the risk of ground gases and vapours at your desk. Then do a ground investigation or assessment. If ground gases are found to be a concern, then measurements using borehole monitoring wells will be made. Existing buildings can be monitored using static measurement methods and diffusion tubes. Monitoring programs can be extended for several days or months, depending on the nature of risk.
Once the investigation is complete the assessment and interpretation of the measurement data will then identify whether there is a risk from ground gases or vapours.
Protection from below ground gasses
Ground gas protection is an extremely specialised operation. GeoShields Ground Gas specialists have the required knowledge, experience and skill levels.
Ground gas protection is often achieved by ventilation and ground membranes in construction. This provides primary and secondary protection against the ingress of gases. Foundation-based ground gas protection will not work if you are an existing homeowner. Ventilation is key. Ventilation can use a combination of natural ventilation for suspended floors, improved underfloor ventilation and the introduction of mechanical ventilation systems so that the harmful ground gases can be safely controlled and vented away from the property. In all cases validation of the construction and the installation techniques is important.
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 is the potential impact of not doing anything?
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. Radon can cause lung cancer. Carbon Dioxide can cause asphyxiation and can be deadly. Methane, Volatile organic compounds, and Methane can all be explosive/flammable. Even low levels of methane, such as 5% or less, can cause methane to become explosive.
The property may be deemed too dangerous for mortgage lenders.
What is Ground Gas Membrane?
Ground gases are dangerous and buildings need to be protected. This protects the structure’s integrity as well as anyone inside it. Protective measures include the use of a ground gas membrane.
Ground gas protection membranes are often made of polymers, but may also contain other materials such as aluminium. They are lightweight, flexible, and easily formable. They prevent gas from flowing into the building from the ground.
To ensure the installation of your gas protection systems meets the required legislation & regulations please call our Sunderland team
Other areas near Sunderland we cover include: