Swim To The Underwater Room (aka The Bubble Room).
Jordan (co-inventor) is camera man for this shot. The ring is made out of super heavy duty galvanized steel pipe that has been cut and welded into an octagon. Gussets where also welded into the inside corners for re-enforcement. Air is regularly refreshed with a SCUBA tank. The biggest danger is something called Pulmonary Barotrauma. That basically means over-expanded lungs. If you take a breath in the room the air you breathe in is compressed (because of the weight of the water above you). If you hold that breath and swim to the surface the air will expand in your lungs and can cause catastrophic damage or death.