Gang,
Just to add it to the post, there is no requirement for redundancy to dive either the pit or the tunnel. The pit has never had that requirement and will not in any foreseeable future.
There is a permit that you have to fill out to dive the tunnel, if you are caught diving the tunnel without a permit the rangers can arrest you for trespassing. That way if you do something in the tunnel that causes you to get hurt and you weren't supposed to be there, in Ohio if you are trespassing the fault lies with you, not the property owner.
The permit has the question of what redundancy you have, however, ... and if you say "nothing" you had better have a good reason or your permit will be denied. This is a free service and it is a requirement of the park... like someone said "their quarry, thier rules." Many people who read the permit have decided that the tunnel may not be for them, which is what it is for.
You can check out
White Star Quarry, Gibsonburg, Ohio one of the best inland dive sites in the midwestern USA. Midwest dive sight. and read the permit under the forms heading yourself. Pretty simple, dive within your limitations and if you aren't absolutely sure of success, don't dive it. There is an advanced open water requirement since the entrance is deeper than 60 feet and you are required to dive the tunnel with a buddy.
Also, if someone tells you that the tunnel is "safe" it is still an overhead environment and the rules were put into place because someone actually got seriously hurt in the tunnel. I really don't want that to happen again.
Dive safe,
Rich