{HEAD ~ A gas blast switch} has a housing which encloses an arcing chamber, an accumulator space and {TAIL ~ an expansion space} 
has
{ HEAD ~ A gas blast switch } has a housing which encloses an arcing chamber , an accumulator space and { TAIL ~ an expansion space }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL