As the temperature is raised to a level at which {HEAD ~ the heating elements} would be damaged, a substantially neutral atomsphere is maintained in {TAIL ~ the chamber} 
As the temperature is raised to a level at which { HEAD ~ the heating elements } would be damaged , a substantially neutral atomsphere is maintained in { TAIL ~ the chamber }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL