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Gas Sampling Using Gresham Tubes Gresham
tubes should not be used for taking gas samples from 19mm diameter boreholes
for subsequent laboratory analysis. A borehole of 19mm diameter will contain a volume of gas equal to:
Some of the borehole gas would have been consumed when using in-situ gas measuring equipment and also when purging the Gresham tube. Hence air is bound to be pulled in to the borehole during filling, rendering the subsequent analytical data meaningless. Corresponding figures for 600mm diameter boreholes are as follows:
Dilution by atmospheric air when taking a Gresham sample is hence far less significant.
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