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