A gas escape and monitor pipe 22 at the lowest level of the gas in {HEAD ~ the area} 23 within {TAIL ~ the housing} 18 allows for gas to escape, and can give an indication of the lowest level of the reducing gas at 23 
within
A gas escape and monitor pipe 22 at the lowest level of the gas in { HEAD ~ the area } 23 within { TAIL ~ the housing } 18 allows for gas to escape , and can give an indication of the lowest level of the reducing gas at 23
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