{HEAD ~ The unit} may also have a tubing to allow oxygen or {TAIL ~ another treated gas} to come in 
{ HEAD ~ The unit } may also have a tubing to allow oxygen or { TAIL ~ another treated gas } to come in
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH