If the switch fails open, the potential at the load side of the switch will drop, and the second diode will allow {HEAD ~ current} to flow to the load through {TAIL ~ the circuit} 
to flow through
If the switch fails open , the potential at the load side of the switch will drop , and the second diode will allow { HEAD ~ current } to flow to the load through { TAIL ~ the circuit }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL