What does the DEP manual mean by cavern/cave shaft? Are they talking about the entire system or just the entrance. Sounds like the entire system, but I wonder if they'd consider 15 minute intervals between dive teams entering? This would effectively space out the teams and reduce the chances of bottle necking. I don't know that you'd be doing more than 15 minutes deco on O2 in Madison anyway (if you had any deco at all) unless you were really doing an agressive dive.
