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