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 {TAIL ~ the load} through the circuit 
to flow to
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 { TAIL ~ the load } through 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 REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH