One of the most common myths about scuba diving is that the tank is full of pure oxygen. It is not. Recreational scuba tanks hold ordinary filtered air, the very same 21% oxygen and 79% nitrogen you are breathing right now, simply compressed to fit a lot of it into a small cylinder. There is nothing exotic about the gas you breathe underwater. The compression is what lets you stay down for the better part of an hour, and understanding what is actually in the tank takes away a lot of the mystery and worry that beginners feel before their first dive.
Just compressed air
The air in your tank is filtered and dried to remove moisture and impurities, then squeezed to high pressure. That is the only difference from the air in the room around you.
Because it is the same familiar mix, your body knows exactly what to do with it. Breathing underwater feels natural within a minute or two.
Why not pure oxygen
Pure oxygen actually becomes toxic under the pressure of depth, so it is never used for recreational diving. It appears only in specialized technical diving with careful training and specific limits.
The nitrogen in normal air is harmless to breathe, but it is the reason we manage depth and time carefully. That balance is the heart of safe diving.
Managing the nitrogen
As you breathe compressed air at depth, your body absorbs a little extra nitrogen, which is why we ascend slowly and observe no-decompression limits. This lets the nitrogen leave your body gently and safely.
Your instructor and dive computer track this for you on every dive. Following the plan is all it takes to keep it a non-issue.
Nothing to fear in the tank
Knowing you are breathing plain air, not some pressurized or dangerous gas, is a genuine relief for many first-timers. The equipment simply delivers normal air at a comfortable pressure.
A Discover Scuba dive is the easiest way to feel how natural it is. See our courses and dives to take that first easy breath underwater.
A word on nitrox
You may hear about nitrox, or enriched air, which simply has a slightly higher oxygen percentage than normal air. It can extend your bottom time on some dives and requires a short specialty course.
It is still not pure oxygen, and it is entirely optional for recreational diving. Standard filtered air is perfect for the reefs of Isla Fuerte.
