Methane & CO2
British Standard 8485:2015 is the “Code of practice for the design of protective measures for methane and carbon dioxide ground gases for new buildings”.
How to deal with gas affected sites
The first thing to do with a new site is to ensure that all gas risks are considered. These results will then dictate both the guidelines that should be considered and the protective measures that should be implemented.
For any new build site using BS 8485:2015 as guidance, the first step is the site investigation that places the site within its characteristic situation.
This ‘CS rating’ is dependent on both the gas levels and flow rates of the individual site, and range from CS1 (very low risk, requiring no protection) to CS6 (such high risk that some sites cannot be built on).
However, it's very difficult to comply with both BS8102 and BS8485.
The contaminated ground industry works in the opposite way to the waterproofing industry and BS is clearly written for above ground structures and does not translate to below ground structures.
The waterproofing industry and standards try to stop water with Types A and/or B then, expecting defects, we manage the remaining seepage using Type C
The contaminated ground industry try to minimise the pressure then use a barrier as second line of defense
This is fine above ground but when we come below ground external ventilation techniques will not work as we are designing for a full head of water which will block ventilation. Unfortunately, the BS8485 and the BS8102 do not correlate very well because of this and we have to design to comply with both.
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Maclennan have been experts in designing, installing and guaranteeing systems for over 30 years.
The first step to truly effective ground gas mitigation is effective assessment. By utilising a site investigation alongside a conscious radon risk investigation that employs Public Health England’s resources and/or a full gas test, then a thorough solution can be formulated.
However, on a site that is at risk from carbon dioxide, methane, and/or radon and water ingress (as well as Hydrocarbon and VOC contamination), the best protection against all dangers is the pressurised and sealed internal membrane system. Not only is the protection absolute, but the safety benefits also provide the most valuable feature of all – peace of mind.
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