I was wondering about accidents in general when the first attempts to use breathing devices underwater were being developed. Before any classes or training. Who were the Wright brothers of diving?
When man first discovered boats were a way to travel across the water he soon discovered that diving was needed if he was to recover the boat and/or its cargo.
I don’t know if there are any diving pics on cave walls but it wasn’t long after that when diving research started. Even in the time of Columbus, which could be called modern, they were diving fairly deep and recovering cargo from sunken vessels.
So to answer tour question, a long flippin time.

Gary D.