The ATC Contingency Anchor is a rigging option that is very versatile. To rig the ATC Contingency Anchor:
Note that if you use the ATC Contingency Method, you can rappel on either strand (i.e. it isolates strands) and both strands have contingency. This speeds up large groups because the second person can be hooking up while the first person is still rappelling. It also gives each person the option to rappel single or double strand.
The ATC Contingency Anchor is very straight forward to convert to a lower, but it is much easier with two people. To convert the ATC Contingency Anchor to a lower (if the rappeller gets stuck on rappel):
Note that steps 2 and 3 can be done simultaneously as long as the first person doesn't let rope out faster than the second person can pull rope through the Totem.
CAUTION: Because the ATC Contingency Anchor method is relying on friction through the ATC, which is not locked off, there is the potential for the rope to creep through the ATC, or even slide uncontrollably through the ATC. Small ropes, heavy rappellers, or not-smooth rappellers, may all cause this method to fail. Please test your combination of gear in a safe environment before taking this method into the field. Additionally, it is crucial to have a belayer (either at the top or the bottom) hold the non-rappel strand in case it starts to slip through the ATC.