In the past deep sea divers had suits with heavy helmets and an air hose attached. There are stories of the air failing. Because of the extreme pressure, they have found nothing

Portrait of a Scaphander — The Public Domain Review

How Cave Diving Works

Have divers ever been accidentally abandoned at sea? - Quora

Why do some divers use rebreathers? - Quora

How do cave divers endure the very long hours of decompression in darkness? - Quora

History of scuba diving - Wikipedia

Underwater & Hyperbaric Welding

How deep could someone dive breathing air through an unblockable tube to the surface? - Quora

What does it look like when a human body has been crushed by the pressure in the deep sea? Where can I find a photo? - Quora

Inventor shows off 'Iron Man'-like diving suit