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Clean Air Blanket Case Study – Primary School, Blackpool
Baron Road was chosen as the best location for this new £5m primary school due to its town centre location and the immediate availability of the brown field Site.
Guidance from CIRIA report C665 ‘Assessing Risks Posed By Hazardous Ground Gases to Buildings’ uses gas concentrations and flow rates to calculate the Gas Screening Value (GSV). The GSV for the worst case scenario is then used to categorise the site as defined in report C665. The GSV for this site has been calculated using the highest value recorded for Methane (12.3%) and Carbon dioxide (8.0%) and the highest flow reading (23.9 l/h). The GSV for Methane is 2.94 l/h and carbon dioxide is 1.9 l/h. Using these values the site falls into the category of ‘Characteristic Situation 3’ (Moderate Risk) for which specialised ground gas protective measures are required.
As the proposed development was a school it is also appropriate to use the points system given in BS8485:2007 ‘Code of Practice for characterisation and remediation from ground gas in affected developments’ as it defines public buildings (including schools) as a separate category. This system still uses the Characteristic Situation scenario but for required protection measures a certain number of points have to be achieved through the construction method. Therefore for ‘Characteristic Situation 3’ a total of 3 points have to be scored. This was achieved by the installation of a Clean Air Blanket system of gas protection.
