I don't usually post on these forums but I feel I have to. I was at the scene after the fact.
This new open water instructor took two new divers into a cave. They had to go through a restriction to enter (one person can fit through at a time). The top of the mound was at 40' and a few feet beyond that you lost all ambient light. viz varied from 10 to 40 feet depending on the depth. As you followed the permanent line down close to 100' the ceiling and the floor met ( a typical florida sink hole) but it had black talcome powder type silt.
He convinced them that he was a technical expert , I talked to him and I know he never dove with helium and probably never had a set of doubles on his back so his stories about depth are ficticious (see blog on my space "project 1100") .
DON'T GO INTO A CAVERN OR CAVE WITH ANYONE INCLUDING OPEN WATER INSTRUCTORS UNLESS YOU ARE TRAINED TO DO SO OR ARE IN TRAINING WITH A CAVERN OR CAVE INSTRUCTOR! It's real lucky we didn't have 3 fatalities.
The rules of accident analysis are;
Training (none were trained even for cavern)
Guidline (they followed a pernmanent line down but the instructor left the line)
Air (use 1 third to enter and two thirds for exit, the instructor started in with a half a tank)
Depth (cavern depth limit is 100', they kinda stayed with in this limit) (one out a four)
lights (carry at least 3 lights per diver and have redundent air supply, they were set up for open water)
I feel bad for the family and fellow divers, I just don't want to see this scene keep repeating.
Dive safe