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Ground gas risk assessment

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Hazardous and potentially life threatening toxic, suffocating, explosive or inflammable concentrations of ground gas such as carbon dioxide CO2, Methane CH4 Hydrogen Sulfide H2S can be found naturally (eg peat bogs, meandering river systems, silted estuaries) or in man-made environments such as landfill sites, infilled quarries docks and canals and infilled mine shafts. Hazardous gases and Volatile Organic Compounds VOCs can be found former petrol filling stations, petroleum works and storage facilities former gas works, tar works etc.

Mine gas is any of various harmful vapours produced during mining operations. The gases are frequently called damps (German Dampf, “vapour”). Firedamp is a gas that occurs naturally in coal seams. The gas is nearly always methane (CH4) and is highly inflammable and explosive when present in the air in a proportion of 5 to 14 percent. White damp, or carbon monoxide (CO), is a particularly toxic gas; as little as 0.1 percent can cause death within a few minutes. It is a product of the incomplete combustion of carbon and is formed in coal mines chiefly by the oxidation of coal, particularly in those mines where spontaneous combustion occurs. Black damp is an atmosphere in which a flame lamp will not burn, usually because of an excess of carbon dioxide (CO2) and nitrogen in the air. Stinkdamp is the name given by miners to hydrogen sulfide (H2S) because of its characteristic smell of rotten eggs. After damp is the mixture of gases found in a mine after an explosion or fire.

Some mines produced more methane gas and were called “fiery” mines. Though a mine may have been abandoned many years before there is the risk that the gases contained within it can seep or migrate to surface via pathways such as interconnecting workings, shafts, adits, geological faults and fracture zones. Exploratory Boreholes from surface sunk to investigate workings or made for geothermal energy recovery could also create gas pathways and care is needed to properly seal such openings to safeguard against this risk.

Radon gas is another potentially harmful natural ground gas which needs consideration.

Geoinvestigate provides a full gas monitoring and evaluation service from initial preliminary gas risk assessment to the installation of Gas wells and the on-site measurement of gas concentrations.