A fugitive gas pipe supplies the fugitive gases to the air intake and {HEAD ~ a vent} allows {TAIL ~ the fugitive gases} to vent to atmosphere 
allows
A fugitive gas pipe supplies the fugitive gases to the air intake and { HEAD ~ a vent } allows { TAIL ~ the fugitive gases } to vent to atmosphere
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH