{HEAD ~ The gas} and vapor evolved in {TAIL ~ these zones} passes upwardly through the vents 94 into the vapor collection region 89 and is removed 
evolved in
{ HEAD ~ The gas } and vapor evolved in { TAIL ~ these zones } passes upwardly through the vents 94 into the vapor collection region 89 and is removed
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH