When I was a young freediver I survived three blackouts. The first one was in a pool doing static apnea. A French freediver brought me up and a female lifeguard got me breathing. The second was when a female DM/instructor realized I had been on the surface a while and hadn't moved. She found me unconscious with the snorkel in my mouth, but clear of water from the expansion method when a SWBO occurred. I had spent too much time at 100 feet smiling and profiling for the tourists. The last blackout was during a class. The student, who I had taught to do rescue the day before, saved me after a deep water blackout when I was under for over 5 minutes. I was lucky to have survived.
A couple years ago, I wrote PSAI's freediving manual and suggested divers follow US Navy Captain Dr. Frank Butler's advice and not hold one's breath longer than one minute. Blood gas analysis on Ama freedivers (Japanese and Korean women who freedive for a living hunting and gathering in the sea) showed significant hypoxia after 1 minute. I say learn from the Ama = A Minute Always, no longer. I show a slide in freediving classes showing that the signs and symptoms of hypoxia correlate with all of the spiritual yogi-like mumbo jumbo and subjective feelings that make freedivers like the sport. As more training agencies adopt freediving courses, there needs to be a shift away from the competitiveness of freediving to the safety aspects. Deep air records on scuba are no longer macho or a demonstration of diving prowess as they used to be. That is not to knock the courage and talent of those who paved the way in either endeavor. But, thanks to science and the experiences of those who survived the old days and those who didn't, we now know better.
Just as we know that there are better alternatives to diving deep air, if a diver wishes to remain at depth during an apnea dive longer than science says is safe, the alternative is scuba. Freediving has no business in the cavern or cave environments. Diving in any significant overhead other than possibly a small attraction sunk in a training quarry such as a cabin cruiser, school bus, or plane is too risky. Not just for the freediver, but for the environment, access to the site, and cavern/cave divers in the overhead. The practice should be discouraged. Open water divers have no business in caverns. An open water diver without the ability to breathe has even less. With the popularity of freediving exploding and agencies selling the idea that holding one's breath for a long time is cool, the rising death toll needs to stay away from our caves.
Want to see the inside of a cavern or cave? Take a course and earn the privilege like those of us who are certified cave divers.