> The awful bit was that he got delayed coming back, wasn't sure how far it was, went to the limit of his air, turned the little knob that gives you the last five minutes, and used that time scratching out a goodbye to his family on the air tank.
I find the scenario as you describe really hard to believe. What you describe is called "J Valve" tank, which had a spring valve that would artificially stop the air flow at around 500psi. The idea was that you would use the tank until it got hard to breathe, then pull a lever that would let you use the last 500psi. It was a great idea in the early days before people started using pressure gauges. J-Valve tanks have been obsolete for years!
I agree that cave diving is extremely dangerous, but no one in his right mind would do it with vintage gear. Unless, by a "few years" you mean 30 or so.