This structure is particularly useful if {HEAD ~ the supply} 94 includes a quantity of {TAIL ~ toxic gases} 
This structure is particularly useful if { HEAD ~ the supply } 94 includes a quantity of { TAIL ~ toxic gases }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL