>> have you ever seen anything even remotely close to this challenge? >> i have not personally, no. nothing that i've been involved in. i have done a few rescues where conditions have been silted out. a cave is an unforgiving environment. when you cannot see, you lose that sense. and that means braille. the goal line becomes that much more critical. so hats off to these divers, and they're probably best in the world. they do dive a lot of sumps and that's exactly what this cave is. >> and you know some of them. have you heard from them? >> i have not heard from them. i do know rick stanton, one of the key individuals, and rick is very equipped for doing this kind of thing. richard harris. i do know of a few of them, in the community, very small community, maybe 5% of the diving community in the world are cave divers. and at this level of diving, you can narrow that down to perhaps another 3%. >> it's really remarkable. what is your sense in watching what they're doing now, which is trying to restore the oxygen to