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INfrastructure Joanne Kwan, CIRIA, Hugh Mallet and Louise Taffel-Andureau, Buro Happold discuss the issues that are still caused by the presence of hazardous ground gas Hazardous ground gases are there still problems 20years on? Following the high profile gas explosions at Loscoe and Abbeystead during the 1980s, several reports were published in the 1990s on the measurement of soil gases, the assessment of risk such gases may present along with the measures that can be employed to manage them. Where do methane, carbon Loscoe, Derbyshire From meteorological records it was clear dioxide, radon and organic At Loscoe, landfill gas migrating from a that before the explosion they had shown recently capped landfill in coal measures a rapid decrease in atmospheric pressure vapour come from? caused an explosion that demolished in advance of a weather front crossing the Some of these gases occur naturally in the a bungalow and severely injured the site. Over a period of seven hours the environment, eg buried organic matter two occupants in 1986 (Figure 1). The atmospheric pressure had rapidly fallen has the potential to generate methane explosion was induced by the central by 29 mb with hourly drops in pressure and carbon dioxide (as well as many other heating boiler starting up in the early ranging between 3.3 mb and 4.8 mb. This “trace” gases). There are numerous sources morning after a significant portion of starkly illustrates the greater egress of gas of these gases derived from anthropogenic the lowest part of the bungalow had during periods of rapidly falling pressure, sources (eg landfill sites, Made Ground/ fill, accumulated an explosive mixture particularly when atmospheric pressure sewage sludges etc) and natural sources of landfill gas and air in the previous has been relatively high and stable during (radon emitting rocks, peat and alluvium few hours. the previous days and weeks. etc). Each of the sources is characterised by the nature/ type of gas and its range of King et al, 1988 concentrations/ rates of generation. What is the problem? The most commonly recognised hazards and effects of soil gases include: flammable/explosive physiological effects odour effects on vegetation. Management Figure 2 illustrates the structured procedure for the assessment of hazardous soil gases. The basis for this flow chart is the framework that was adopted for the Environment Agency’s model procedures (Environment Agency, 2004). Figure 1 Landfill gas caused an explosion that demolished a bungalow and severely injured the two occupants, Loscoe, Derbyshire 20


evolutionwinter2012
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