I took my daughter (20 years old, less than 10 dives) on a dive to 48 feet.
I had got a small, ladies style bc from a neighbor. When I got it, the power inflator didn't work. I replaced it myself, then took it to a local dive shop to have my work verified and the bc itself looked over. The dive shop owner basically did what I had done. He tugged on everything that could come loose to see if there was any dry rotting. He connected it to a tank and tested all the functionality. Then he filled it again and let it sit for a while to see if it leaked. Everything checked out.
Just before splashing and after the buddy check, my daughter thought there was a leak where the inflator hose connects to the bc. I tightened the connector, and it appeared to solve the problem.
I conducted a weight check, and she was properly weighted at 8 pounds (she's pretty slight and was using a 63 cu. ft. tank).
We conducted most of the dive without incident. She let me know when she got to 1000 psi, and we started to ascend slowly. As we began to ascend, I saw that her inflator hose was completely disconnected from her bc and was held in place only by the lp hose from the regulator.
She was unaware of any problem, and didn't have any trouble ascending to our safety stop because she wasn't overweighted and the tank would have been positively buoyant at that point. However, she was puzzled as to why I was holding on to her bc throughout the ascent.
Although I had been watching her closely, I neither saw the hose disconnect nor saw any release of air, so I don't know when failure occurred. I was swimming on her right side for nearly the entire dive. I'm guessing that, because she had very little if any air in the bladder at depth, there were no visual or sound effects when it failed. But I'm guessing here: I don't know when it failed. It could have been as early as when she dumped air to descend.
Upon inspection afterwards, the threads on the bc side of the connecter had broken. Part of the bc's threading was still in the threading of the inflator hose's connection.
I don't know if this qualifies as a near miss because there was never any sense of urgency in anything either of us did, but I am wondering what I could have done different.
The three opportunities I had to do something different seem to have been 1) deciding to use the used bc, 2) addressing the leak pre-dive, and 3) swimming on both sides of her from time to time so I could see all of her gear configuration.
Thoughts? What could I have done different?
