Bob Simon: Nobody would choose to do that.
Tanya Streeter: No. But, you know, you sort of find yourself there at that point on your journey, and realize that that's what you signed up for. So it's all par for the course.
Tanya and other free top divers go to the remotest part of the Bahamas called Long Island which is the Mecca of free diving. Christopher Columbus put Long Island on the map in 1492 but you'll have trouble finding it on any tourist map today. The jet set doesn't come here because jet planes don't fly here from America or Europe. There are hardly any hotels, no golf courses, no frozen margaritas.
Right off the beach there is a massive limestone cavern called Dean's Blue Hole. It is 663 feet deep, and it is dangerous. A few days after we left, a teenager dove into the Blue Hole and didn't come up. His body was never found.
This is where William Trubridge lives and trains. For the last six months, he's led a monastic existence, getting ready to try for another world record. He wants to make it down to 410 feet on one breath. This time using a single fin. To get ready he goes through a unique a set of exercises that he designed himself to make his body more flexible and supple, more like a dolphin. His waist here is 27 inches.
Then the countdown. His wife Brittany is on the platform. His parents are on the shore. The judges and safety divers are in the water. Their job: to save him if he loses consciousness.
In any other sport, a spurt of adrenalin would be a good thing. Not here -- tension, anxiety consume oxygen -- what you need is serenity.
He begins to swallow air. He is literally swallowing air, packing his lungs with more air than they could receive from breathing alone. Free divers discovered this technique themselves to expand their lungs. And in his head?
William Trubridge: Sometimes if I'm taking my last breath, a voice will pop into my mind saying, "This-- this is-- could be your last breath of your life." Or, "You're gonna die." It's kind of like the devil's advocate sitting on your shoulder whose going to think of the worst possible thing and voice that in your mind.
Bob Simon: The devil is still talking to you?
William Trubridge: Always. Yeah.
His lungs are now the size of watermelons. As he descends, they will be squeezed until they're no larger than oranges. His heartbeat slows down to 27 beats a minute. His mother is counting seconds. Down deep, the Blue Hole becomes the Black Hole.
William Trubridge: You're alone with yourself down there at depth. And the-- even your body slips away so that it feels like you're just a kind of a speck of consciousness that's floating into the abyss. You're weightless. There's no light, no sound and so it's almost as if you're floating in a completely empty tank.
The pressure is causing his brain to absorb more nitrogen. He is feeling light-headed, kind of drunk. It happens to all divers deep down. It's called narcosis. Suddenly, a bright light on the base plate 410 feet down. He takes his tag and begins his ascent.
At 100 feet he is joined by his safety divers like a pod of dolphins, they guide him through the most hazardous part of the dive, running out of oxygen can cause a blackout.
The sound you are hearing is William expelling air from his sinuses.
He's made it, but for his record of 410 feet to be ratified by the judges he needs to perform three simple tasks when he gets to the surface, take his goggles off, give the OK sign with his fingers and say, "l'm OK" in that precise order. Sounds simple but William's brain isn't working. He does these things in the wrong order. The judges disqualify him.