Further, it is preferred that the air be available at {HEAD ~ at least about 0.5 standard cubic feet} per {TAIL ~ minute}  
per
Further , it is preferred that the air be available at { HEAD ~ at least about 0.5 standard cubic feet } per { TAIL ~ minute }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH