A diver who descends 200 feet beneath the surface of the water breathing air from a scuba tank is taking a big risk. Safety regulations for recreational divers limit them to 130 feet. Even specially trained scientific divers are required to stay above 190 feet or they lose their certification. So, it’s risky, but it’s been done. Lots of divers have done it, included Jacques Cousteau who was one of the inventors of SCUBA equipment.
Today, we have special equipment, gas mixes and training that makes deep diving safe, so no one needs to risk their life diving deep on air, but some still do. They do what’s called Bounce Diving, shooting down to depth as quickly as they can and then swimming back up to the surface. Some have even gone as far as 300 feet. There are reports of people going deeper and surviving, but many more reports of divers trying and not returning.
Past 100 feet, nitrogen narcosis makes divers feel drunk and unable to make sound decisions.
Past 190 feet, Oxygen toxicity can cause them to convulse and die. Period.
Want More Explanation?
When divers breath air underwater, the pressure affects the way the molecules of air get into the blood. (namely, how many molecules get in there). At about 50 feet or so, the nitrogen in air starts to affect a diver’s thinking capacity. By 100 feet, a diver can feel quite impaired, drunk even. They call it Nitrogen Narcosis, or rapture of the deep. It gets worsse the deeper a diver goes.
To fend off Nitrogen Narcosis, divers will change the percentage of nitrogen in their tank. Adding oxygen creates a mix they call Nitrox. It reduces narcosis, but greatly limits their depth because as pressure goes up, oxygen becomes more toxic. The more oxygen they add, the shallower their maximum depth limit should be.
So how do they dive to 200 feet? They mix in another gas. Instead of replacing some of the nitrogen with more oxygen, they replace it with helium. The mix is called trimix. Heliox consists of just helium and oxygen. To get even more technical, they sometimes add argon because at a certain depth helium becomes toxic also.
Hopefully you can see our point: this stuff is complex. It’s technical. And if you don’t know what you’re doing, it’s dangerous, but not at all impossible.