I know quite well about diving. I'm not a diver but if anyone has read <Shadow Divers>, you know what kind of risks divers have to deal with.
Diving to 33 meters without air requires super human capability. You need to be able to dive down really fast and come up carefully. Actually a diver shouldn't breath under deep water if he really needs to come up quickly. If you breath, you'll need to spend in the water for at least 2 hours.