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