I seem to remember learning about shallow water blackout when I was training as a lifeguard, and when I took my scuba training. My (certainly simplified) understanding was that when you hyperventilate, you decrease the CO2 concentration in your blood, which eases your urge to breathe. If your oxygen level drops enough, you pass out, and may drown.
spogga: Yes, people can learn to float, but a complete non-swimmer’s instinctual reaction is not to float, call for help or effectively swim even a couple meters to safety. There’s a good description in the first link on this page: http://www.pia-enterprises.com/retrieval.html Warning, it’s a word document. It’s what I had been taught to recognise, and it’s what a non-swimmer in a pool has looked like when I’ve seen it happen, panicked, wildly moving their arms, and certainly not not successfully floating.
I’m not sure if this technically falls into the category of your question, but i’d say, yes, it is possible for someone to die from “holding their breath”
There’s a sleep disorder called Central (not to be confussed with obstructive) sleep apnea. WHat happens is - for unkown reaons, while you sleep, many times throughout the night your brain forgets to tell your body to breathe. People have been known to die from sleep apnea.
When someone with apnea (this applies to both obstructive and central) stops breathing in the night, their oxygen levels drop - sometimes they drop VERY low - i’ve heard of several cases (from the actual person, not a story from someone who heard from someone else) where the oxygen levels droped well below 40%!! (if doctors come across someone with oxygen levels below 90% they’ll put them straight on oxygen so you can imagine what kind of damage these REALLY low levels must be doing to a person’s brain etc)…anyway, once the oxygen levels drop, the body will wake itself up and you’ll start breathing again… problem is if something prevents you from waking up easily when this occurs (things like alcohol, muscle relaxants, sleeping pills etc) you die.
CHM:Having thought the matter through I have to agree with you in that a non swimmer will not assess the situation calmly but will as you say not float or call for help but will instead flail about using up energy and will eventually sink through exhaustion.
I’ve never been scuba diving but intend to try it in the not to distant future, it looks real good.
i was on the swimming team at the time in high shcool, and i used to ( for fun ) swim two laps ( 50 yards ) under water on a single breath. well this one time i was on a diet and not feeling very strong, i just sat in the sauna for about 15 minutes and when i was swimming under water i held my breath for a bit too long and passed out ( under water ) .
i was lucky that they actually noticed my body floating around, and pulled me out, and resuscitated my ass
it’s freaky when you get close to the actual passing out.
I was also swimming underwater (3.5 lengths of a 25 yd pool) and right before i passed out, i remember the tunnel vision then blackness. I actually remember it being black… and I remember when it was black, pushing off the bottom of the pool. The next thing i remember was two guys holding me out of the water and coughing a lot
