All divers must always know what gases they are breathing. Divers must also understand how being underwater affects those gases and how those changes affect their body.
As we breathe diving gases at greater and greater depths, the increased pressure required to fill our lungs starts to affect gas behavior. Water cannot be compressed, but in contrast, gases can be compressed.
Diving too deep with gases can have serious effects on a diver’s body and can cause serious injury, even death.