Kim:
I have recently heard about a cave here in Japan that is shallow water - maximum 30 ft - with air available above the water in the cave. Now I know that with my overhead cert I am only trained to penetrate a flooded cave/cavern to the limit of natural light penetration. What would be the situation in such a cave as I described above? Would diving such areas be counted as diving in an overhead as there is available air above?
The danger with the half flooded cave is that divers might go under an overhead without realizing that they no longer have direct access to the surface, especially, if they have really cool 18w HID lights that chase away the darkness.
There's a place like that in the USA- Bonne Terre Mines. They use it for open water training dives, but there are lights strung up everywhere overhead, they don't allow powerful dive lights, and it's more or less a guided tour with safety divers.
If this half flooded cave has an ambient light zone, then I think it would be fine as long as you follow the cavern guidelines- buddy teams, backup lights, continuous line to open water (or maybe entry point, in this case), and rule of thirds. This would be to protect you in case you did end up under an overhead. If it does have an ambient light zone, that this is probably an ideal place to practice reel skills, lights out drills etc.
I would also check to see what the local custom is- maybe it is set up to be safe for open water dives or maybe 60 people have died there in the last year. Local dives shops would be a good place to start, if you haven't already checked there.
