Gas screen

These results gave a gas screening value of 0.072 which indicated characteristic situation 2 (see Chapter 6). However, the results only just exceeded the threshold for this characteristic situation and given the nature of the source it was considered unlikely that further results would increase the characteristic situation (either the concentration or flow rate would need to increase by a factor of 10) and so further monitoring was not required. 

CIRIA Report C659/665 has two methods of characterising the level of risk associated with a site, one that has heen specifically developed for the NHBC that applies for low rise housing and the other for any other type of development. Both methods use the gas screening value (GSV) to characterise a site. The GSV is given by ... 

The gas screening value is the maximum value obtained from all the wells... 

Typical maximum concentration (%v/v) Gas screening value (l/h) Typical maximum concentration (%v/v) Gas screening value " (l/h)... 

The Gas Screening Value thresholds should not generally be exceeded without the completion of a detailed gas risk assessment taking into account site-specific conditions. 

Characteristic Situation (CIRIA 149)2+6 Risk classifi- cation Gas screening value (CH.orCOp (l/h) Additional factors Typical source of generation ... 

Gas screening value (litres of gas/hour) is calculated by multiplying the maximum gas concentration (%) by the maximum measured borehole flow rate Site characterisation should be based on gas monitoring of concentrations and borehole flow rates for the minimum periods defined in Section 5... 

Gas screening value l/h Gas screening value l/h Gas screening value l/h Housing... 

Free Moisture (HOC), Oil Absorption Surface Area, a2/ga Screen Analysis ... 

The Air Force/Hughes cell is illustrated m Figure 9.22. It consists of a stack of nickel electrodes, separators, hydrogen electrodes, and gas screens assembled in a recirculation configuration. In this... 

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