UK is experiencing a growing concern about harmful, naturally occurring underground gases and vapours. To protect both the structure and its users, it is crucial that ground gases are identified and managed.
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.
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 with a history of heavy industrial use, landfills, or spillage of petrol, oil, or solvents can produce dangerous gases such methane and carbon dioxide.
All of the above gases and vapours can have a variety properties such as being toxic, asphyxiating and flammable. Some can chemically interact with concrete and other plastic building materials, affecting its structural integrity. 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)
Radon gas, methane, carbon dioxide, methane and Volatile Organic Compounds (such as hydrocarbons), are dangerous to the health. Constructions that contain these gases must use suitable materials and follow the recommended guidelines.
In accordance with CIRIA C735, an independent ‘Gas protection verification plan’ is required. For gas protection, it is necessary to follow a robust design process and construct the building. Once construction has passed independent verification, handover paperwork should be prepared. This should include any necessary measures during the remaining construction phase, such as to prevent damage and during maintenance and operation.
Specialist advice is highly recommended during the assessment and risk assessment phases of ground gas data. Here are some key documents you should know about and that you can 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
BS8485:2015 + 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. This process can be used to show that the risks posed due to the actual or potential presence of methane and carbon dioxide have been addressed.
To ensure the installation of your gas protection systems meets the required legislation & regulations please call our Croydon team
What is ground gas?
What has happened to ground gas?
Ground gases weren’t considered to be a threat to buildings and users in the past. As it is becoming increasingly difficult to find suitable sites for development, there has been an increase in the number of brownfield sites. However, brownfield sites can contain soil and ground pollutants.
Because of increased awareness about the dangers, the Environment Agency has created new legislation that is more strict in dealing with ground gas issues. It has been adopted across the country by local authorities.
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.
Assessing ground gas risk
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. 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 against below ground gases
Ground gas protection is an extremely specialised operation. GeoShields Ground Gas specialists have the required knowledge, experience and skill levels.
The use of ventilation and ground gas membranes during construction is a common way to reduce the danger of ground gases. A foundation-based ground gas protection system is unlikely to be practical if you’re already a homeowner. Therefore ventilation is the key. A combination of natural ventilation on suspended floors, better underfloor ventilation, or the introduction of mechanical ventilation systems can be used to ventilate. The harmful gases can then be safely controlled and vented out of the property. It is crucial to validate the construction and the installation methods in any case.
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 responding to the potential ground-gas risk depends on the type and extent of the ground gas. Some ground gases can affect your health, others may cause damage to 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. Low levels of Methane (5%) can make it flammable.
The property may be deemed too dangerous for mortgage lenders.
What is Ground Gas Membrane, exactly?
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. Ground gas membranes are usually used to protect buildings.
Ground gas protection membranes are typically made from polymers, but can also be made with other materials like aluminium. They are lightweight, flexible, and easily formable. They are designed to stop the gas flowing from the ground and into the building.
To ensure the installation of your gas protection systems meets the required legislation & regulations please call our Croydon team
Other areas near Croydon we cover include: