why people pass out underwater

[uscgrescueswimmer]

This may be a vague ? I have read numerous dive related injuries or death that start out with the diver blacked out underwater. Im just curious to what may lead to this is. I know there are probably 100's of diffrent possibilities I was just looking if there was a common one. Thanks

 

[wedivebc]

Deepwater blackout is thought to be linked to the same anesthetic mechanism that causes narcosis. I am not sure if anyone knows exactly why it occurs but it is usually triggered by a quick deep descent and may also have something to do with CO2 buildup.

 

[Diver0001]

This may be a vague ? I have read numerous dive related injuries or death that start out with the diver blacked out underwater. Im just curious to what may lead to this is. I know there are probably 100's of diffrent possibilities I was just looking if there was a common one. Thanks

If you look at it in the big picture you get a couple of main reasons, I think:

1) Incorrect breathing (CO2 buildup)
2) Incorrect procedures (Too deep, O2 toxicity, CCR incorrectly set up)
3) Poor health (heart attack or other existing medical condition)

R..

 

[Mick_O]

Isn't this what is suspected to have caused the death of Aussie diver Dave Shaw, on his ~880ffw mission to retrieve a 10 year old body?

 

[freediver]

This may be a vague ? I have read numerous dive related injuries or death that start out with the diver blacked out underwater. Im just curious to what may lead to this is. I know there are probably 100's of diffrent possibilities I was just looking if there was a common one. Thanks

I'm sure you were probably referring to scuba or ccr but just from a freediving point of view:
SHALLOW WATER BLACKOUT -- a state of unconsciousness preceded by carbon dioxide retention. Unconsciousness strikes most commonly within 15 feet (five meters) of the surface. This is generally what happens to the person that swims long horizontal distances as the CO2 builds up in the body.

BREATH-HOLD BLACKOUT -- a state of unconsciousness preceded by the gradual onset of hypoxia; risk is compounded by hyperventilation or increased (shallow) underwater activity. Generally occurs to those that are practicing static breath holds.

ASCENT BLACKOUT -- a state of unconsciousness preceded by sudden onset of hypoxia during ascent; risk is compounded by hyperventilation or increased (shallow) underwater activity. This is what most refer to as Shallow Water Blackout. It is actually termed Ascent Blackout as the diver ascends and , upon expansion of the lungs, vital O2 is taken away from the brain and utilized by the lungs. A rapid ascent may increase liklihood as well as exhalation on ascent. Unlike Scuba, exhalation during the entire ascent is not stressed. It is only within the final 5m - 8m that the diver should start to exhale.

 

[Doc Intrepid]

To add to what has been said previously, two mechanisms commonly linked to underwater blackouts are hypoxia and CO2 retention. The latter may be brought about or hastened by higher than common levels of exertion, breathing air deep (helium based mixtures reduce 'work of breathing' (WOB), a measurement of the effort required to allow a regulator to function and the lungs to ventilate properly at depth), and improper breathing - so called 'skip' breathing or rapid shallow breathing often associated with panic or severe anxiety.

With respect to the former, here is a link that offers more information:
http://www.freedive.net/chapters/SWB3.html

 

[uscgrescueswimmer]

Thanks for the info. I was referring to scuba. We had to deal with Shallow water black out during rescue swimmer school. Had to sign waivers stating if we were to hyperventilate during school we would be dropped. I was just curious about the divers you here that are just swimming along on ascent and bam there unconsious. Thanks again

 

[rmediver2002]

CO2 toxicity was the most common cause of blackout among hard hat divers in years past, inadequate ventilation of the helmet was the cause.

It still occurs sometimes, but more often than not now it is overbreathing a regulator, skip breathing, equipment that is not maintained or has been maintained incorrectly.

What they were reffering to in your class was also a common problem at the military dive school. Hyperventilating to improve breath hold can cause levels of CO2 (the CO2 within our system causes the stimulus to breathe) within the body to drop, if pushed to far the diver can actually blackout before CO2 has built back up enough to cause them to surface and breath, while during this breath hold the O2 levels in the divers tissue continue to drop. When low enough the diver can blackout from hypoxia.

 

[leo311]

beautiful explanation. Leo, NREMT-I.

 

[simbrooks]

These are all great examples of the kinds of things that generally can go wrong and lead to unconciousness, are there any less common ones? What about tight neck seals cutting off blood supply to the brain? Either by a DS or a hood tucked into a wetsuit.I dont know how common that is, but wondering if it might also be added.