Gas protection is the prevention or control of the penetration of hazardous

gases Gas is a state of matter that has neither a fixed volume nor a fixed shape and is a compressible fluid. A ''pure gas'' is made up of individual atoms (e.g. a noble gas like neon) or molecules of either a single type of atom ( elements such ...

into buildings or other types of real property. It usually involves either blocking entry pathways or removing the source of the gas.

Hazardous gases

Methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

(which is flammable at 5-15% by volume in air) and

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

(which is toxic) are the most relevant gases, especially following two

gas explosions Gas is a state of matter that has neither a fixed volume nor a fixed shape and is a compressible fluid. A ''pure gas'' is made up of individual atoms (e.g. a noble gas like neon) or molecules of either a single type of atom ( elements such as ...

in the 1980s in

Loscoe Loscoe is a village near Heanor in Derbyshire, England, lying within the civil parish of Heanor and Loscoe. It had prominent coalmines in the 19th and 20th centuries. Denby Common and Codnor Breach are hamlets on the western edge of the villa ...

and

Abbeystead Abbeystead is a small hamlet located in the Forest of Bowland Area of Outstanding Natural Beauty, in Lancashire, England. Abbeystead lies close to the Trough of Bowland but even in medieval times, was considered part of Wyresdale rather than ...

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

. UK regulatory bodies such as

Building Research Establishment The Building Research Establishment (BRE) is a centre of building science in the United Kingdom, owned by charitable organisation the BRE Trust. It is a former Government of the United Kingdom, UK government national laboratory that was privati ...

British Standards British Standards (BS) are the standards produced by the BSI Group which is incorporated under a royal charter and which is formally designated as the national standards body (NSB) for the UK. The BSI Group produces British Standards under th ...

, the

Department of Environment An environmental ministry is a national or subnational government agency politically responsible for the environment and/or natural resources. Various other names are commonly used to identify such agencies, such as Ministry of the Environment, ...

, and others in the construction industry have developed and published guidance for preventing such gasses from entering buildings. Their production in the environment is associated with

coal seams Coal mining is the process of extracting coal from the ground or from a mine. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extra ...

, deposited river silt,

sewage Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produced by a community of people. It is typically transported through a sewerage, sewer system. Sewage consists of wastewater discharged fro ...

landfill A landfill is a site for the disposal of waste materials. It is the oldest and most common form of waste disposal, although the systematic burial of waste with daily, intermediate and final covers only began in the 1940s. In the past, waste was ...

waste, and

peat Peat is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. ''Sphagnum'' moss, also called peat moss, is one of the most ...

. In the case of

landfill gas migration Landfill gas migration is a complex process in which gases produced by waste in a landfill move from the site of original deposition to other places via diffusion, usually from areas of high concentration to low. The process is also affected by th ...

, gas is produced by organic materials in the waste degrading over time. Typically 40% carbon dioxide () and 60% methane () by volume, this gas can be heavier than air or lighter depending on the concentration (which varies from time to time), but will move from an area of high pressure to one at a lower pressure irrespective of its relative density.

Usage

Systems to prevent gas ingress include a passive barrier or, less commonly, an active system. Passive systems utilize a barrier with low permeability, such as a membrane. Active systems are mostly employed on commercial properties because of the associated costs. There are two main practical types of active systems to prevent the ingress of gases into buildings: positive pressurization, and forced ventilation. Gas Membrane 2

Integrity testing

Both passive and active systems require "gas integrity testing", most often using the

NHBC The National House Building Council (NHBC), established in 1936, is the UK's largest provider of new home warranties. NHBC is also the UK's largest single Approved Inspector for Building Regulations. Other activities include the provision of se ...

traffic light system. This is because the conditions under which gas membranes are installed are often difficult and can adversely compromise the integrity required by the manufacturer or client. The purpose of the test is to ensure integrity and allow the installation to be certified if the method of protection performs correctly.

Membrane testing

The membrane is tested immediately after installation and prior to being covered up by any following construction processes. The area below the membrane is temporarily pressurized with a mixture of clean air and a non-toxic and inert

tracer gas A tracer-gas leak testing method is a nondestructive testing method that detects gas leaks. A variety of methods with different sensitivities exist. Tracer-gas leak testing is used in the petrochemical industry, the automotive industry, the constr ...

that is sensitive to detection. Special equipment is then used to trace all leaks within the installation, with particular attention being paid to critical points and junctions formed between the membrane material and other structural elements prior to conducting a sweep of the complete area. Any leaks are identified and sealed, and the membrane is re-tested before it passes and the certificate is issued.

Active system testing

Active systems require a test of the alarm in case of failure of the system or power supply and possible buildup of gas.

References

{{Reflist, 30em

Sources

* BS8485. * Department of the Environment, The control of landfill gas, Waste management paper No 27. * Department of Environment, Landfill sites development control. * Guidance on evaluation of development proposals on sites where Methane and Carbon dioxide are present, incorporating Traffic Lights. Rep Ref.10627-R01-(02) Milton Keynes; National House Building Council. Environmental mitigation Landfill Pollution control technologies