Gas Protection Overview


Material containing either biodegradable or organic content (e.g. domestic refuse, peat, coal seams) has the potential to produce landfill type gases or ‘ground gas’ (typically carbon dioxide, methane and hydrogen sulphide) and can cause a reduction in oxygen levels or create the risk of explosion.

When building on or adjacent to contaminated sites, there is a potential risk for generation of ground gases and the accumulation of these gases below and within buildings. If not appropriately managed ground gases can give rise to flammability, toxicity and asphyxiation hazards as well as vegetation die back. Risks from ground gases are assessed in accordance with current guidance provided in BS 8485 (2007)2 and CIRIA C665 (2007)3.

In order to evaluate potential risks from ground gases at the site, a plausible pollutant linkage must be established using the source (contaminant)–pathway–receptor relationship. A definition of the three essential elements of a pollutant linkage is given in CLR11 (Environment Agency, 2004)4 and shown below.

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Source - Pathway - Receptor

The structure of a building can provide sufficient containment to allow dangerous concentrations of gases to develop and where necessary building foundations require site-specific designed gas protection measures. A conceptual model is created based on the following characteristics of the site. An appropriate gas protection system is designed around the conclusions of this model.


The cause or source of the contamination is identified. For erxample, the source might be a leaking oil tank or contaminated ground or water. The location of the contamination is identified, such as in soils, ground or surface waters or ground gases.


The pathway is the route the source takes to reach the receptor. Pathways include, for example, air, water, soil, animals, vegtables and eco-systems.


If contamination is to cause harm, it must reach a receptor. A receptor is a person, animal, plant, eco-system, property or a controlled water. Each receptor must be identified and their sensitivity to the contaminant must be established.

From the information above, a conceptual model is created displaying the all sources, pathways and receptors. Conclusions are drawn about the potential risks caused by the source of contamination. Conceptual models are used to inform and drive site investigations and to assist with remedial strategies.

SEL Service

Based on appropriate site investigation data SEL Environmental Ltd offer design, supply and installation of a complete gas protection system with particular consideration of system performance, constructability, risk assessment and architectural aesthetics. In offering full system design and installation

SEL is providing all parties involved with the reassurance of a single point of contact. Gas Barriers to Structures SEL have been providing underslab and external gas barrier systems for more than 10years. A typical gas barrier system would comprise a 1mm thick robust welded gas resistant barrier (essential for construction survivability). All the joints of the gas barrier will be heat sealed using hot air welding equipment. Passive Ventilation to Structures

SEL ventilate below the concrete slab of a structure using a synthetic void former in strips or blanket arrangement. This provides a preferential pathway for the gas to escape. Ventilation to atmosphere is achieved using a range of outlets developed to satisfy the requirements of Clients and Architects. Ventilation is achieved passively where possible but active vent measures can be introduced where required.