UK is experiencing an increase in harmful, naturally occurring sub-ground gases and vapours. To protect both the structure and its users, it is crucial that ground gases are identified and managed.
A site could have natural gasses, or they may be the result of an historical use.
Naturally occurring gases include methane, carbon dioxide, nitrogen and radon and many of these can be present within the soil at elevated concentrations relative to normal atmospheric gases.
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.
The gases and vapours listed above can cause cancer if they are not used in sufficient quantities. Some may also chemically interact with the concrete and plastic building materials, affecting the structural integrity of the building. They can be found in buildings and other structures above and below ground.
There are many types of gas.
- 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.
According to CIRIA C735, a separate ‘Gas safety verification plan’ (or ‘Gas protection verification document’) is required. 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.
Specialist advice is highly recommended during the assessment and risk assessment phases of ground gas data. Below are some of the key documents to be aware of and 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 contains recommendations for ground gas site identification and the selection of solutions for designing integral gas protective measures in new buildings to prevent carbon dioxide and methane entry and create a safe environment. It provides a way to demonstrate that potential or actual carbon dioxide and methane risks have been mitigated.
Call our Manchester team today to book your gas protection systems validation inspection
How does ground gas occur?
Why is ground gas becoming a problem?
Ground gases were not considered a danger to buildings or 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. Brownfield sites may contain contaminants that can affect the ground or soil.
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.
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. Existing buildings can be monitored using static measurement methods and diffusion tubes. Depending on the nature and severity of the risk, monitoring programmes can last from days to months.
After the investigation is completed, the interpretation and assessment of the measurement data will determine if there is any risk from ground gases or vapours.
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.
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. Foundation-based ground gas protection is not feasible if you are a homeowner. Ventilation is key. 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, it is important to verify the construction as well as the installation techniques.
Some cases in which the dangers posed by gases or vapours are due a by-product more severe soil and groundwater contamination can be mitigated through the remediation.
What's the impact of not doing something?
The effect of not reacting to potential ground gas risks depends on which type of ground gas was discovered. Some may affect your health while others can damage the integrity of the building. Radiant exposure can lead to lung cancer. Carbon Dioxide may cause death from asphyxiation. Methane (and other volatile organic compounds) can ignite and be 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?
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 can be made from polymers or other materials, such as aluminium. This allows them to be light and flexible while still being formable. They can stop gas from getting into buildings and the ground.
Call our Manchester team today to book your gas protection systems validation inspection
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