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Wherever there is the potential for ground gases to accumulate inside buildings or confined spaces, gas monitoring is carried out. This is to determine the levels of methane, carbon dioxide, oxygen and other gases. This is typically done via gas monitoring standpipes/wells. These are constructed in boreholes using slotted plastic pipe, surrounded by a granular filter sealed at the surface. The standpipe has a gas valve fitted and usually protected by a metal cover.
Gas monitoring involves attaching a specialist gas monitor which records the concentrations of the ground gases and also the flow rate. Groundwater levels can also be determined, as can volatile or semi-volatile organic gases.
From the gas monitoring data, a risk assessment is carried out to determine the requirement for gas protection measures. The process is outlined in CIRIA Report C665, “Assessing risk posed by hazardous gases to buildings” and BS8485: 2015 “Code of Practice” for the Design of Protective Measures for Methane and Carbon Dioxide Ground Gases for New Buildings.
Gas Characteristic Situations (GCS) are determined based on gas concentrations and flow rates to determine the level of protection required. In respect of housing development, a so called ‘Traffic Light’ system is adopted.
Advice is provided as to design of any gas protection measures necessary and also provide verification of the gas protection measures during construction.
