[lamontcg]

With 2 dives and 4 regulators on the team, it takes 3 failures to reduce the whole team down to 1 regulator -- and even then there's ways to survive and get out of the cave.

So more like 100^3 to start with, and then the failure rate in practice is lower than that (I've done 200 cave dives and I've had 1 failure -- and I know many other cave divers with similar levels of experience that have had none).