Gas Protection Background

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.

SEL Gas Protection Solutions

SEL can provide design, supply and installation of a complete gas protection system with particular consideration to performance, constructability, risk assessment and architectural aesthetics to manage most gassing regimes. 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 15years. 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.

SEL taped jointed gas barrier

SEL taped jointed gas barrier, sealing around a service pipe penetration

SEL fully welded gas barrier

SEL fully welded gas barrier with welded joints

SEL sealing a gas membrane to a column penetration

Sealing the gas membranearound a column penetration

SEL welded membrane joint air test

Twin wedge welded membrane joint undergoing an air test to ensure integrity of the seal, carried out in conjunction with SEL's ISO9001 on-site CQA protocol

Passive Ventilation to Structures

SEL ventilate below the concrete slab of a structure using a synthetic void former in strips with aggregate 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.

SEL gas dispersal geocomposite layer

SEL geocomposite gas dispersal blanket being installed below a concrete slab

SEL vent bollard

SEL can supply a variety of vents to suit the site requirements. SEL can offer vent stacks, vent bollards and ground level vents.

SEL gas collection pipework

Gas collection passing through edge beam

Gas Membrane Installation

SEL offers a full managed gas membrane installation service for gas barriers including a hydrocarbon barrier, methane barrier, carbon dioxide barrier and radon barrier. Our in-house fully managed specialised gas membrane installation service enables us to deliver a ‘right first time’ system for domestic and commercial projects. All gas membrane installations are carried out in accordance with our ISO9001 accreditation and on-site CQA. We are also able to source independent third party inspection and validation of our gas membrane installations if required.

SEL welded gas membrane installation

SEL installer joining 2 panels of gas membrane using a twin wedge welder