Key points for design of gas protection systems

A combination of measures is usually used to minimise the risks associated with ground gas. This is so that if one element of the protection fails fhe ofhers will continue to protect the development. Only where the risk posed by the presence of ground gas is very low will a single level of protection be suitable The scope of measures for any site should be related to the risk assessment, with an increasing element of redundancy (or extra protection methods) provided as the risk increases Use of precautionary gas protection without a site investigation is a valid approach for low-risk sites, provided that a desk study is imdertaken to show there are no significant gas sources that could affect the site 

The requirement for redxmdancy in gas protection means that generally at least two different methods are required to ensure protection is maintained if one method fails (e.g. a membrane and ventilated void) 

No single method can provide two types of protection are xmtrue. For example a positive pressurisation system does not provide two levels of protection (a barrier and a ventilation system). If it stops working a second level of protection, such as a membrane, is required to protect a building 

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