scuba diving deeper than 300 feet

[Jimmer]

What if you had a rebreather which keeps the oxygen partial pressure at a safe level, and uses helium for the diluent; how deep could you go, and what would be the limiting factor?

From a PPO2 standpoint, if you had pure O2 and pure He in your cylinders, there would be no limit. Obviously I'm sure there are lots of other limiting factors, HPNS for one I would think. Others can chime in that know a lot more about rebreathers than me.

 

[H2Andy]

I heard u can go up to 300 but to stay safe they only do 150

to sum up what everybody else has said, there are two problems:

1. nitrogen narcosis (really, any inert gas will cause this). the deeper you go, the more narcotic nitrogen (or any inert gas) gets. this seriously impairs your judgment, reaction times, critical thinking, etc... thus making you tremendously dangerous to yourself.

effects begin as soon as you start your dive, but are not usually noticed by most divers until about 100 feet ... most divers will feel severe effects by 150 feet. by 200 feet, you really have to struggle to stay on task. past that, your brain is really fried. some people are better able to deal with it than others.


2. oxygen toxicity: the oxygen in air (21%) will start to become toxic to your system at around 218 feet. this is not a "bright line;" more like a gray area. you can exceed that by quite a lot and still be ok ... or you may lose the roll and get a seizure.

hope this helps

 

[Mr.X]

What if you had a rebreather which keeps the oxygen partial pressure at a safe level, and uses helium for the diluent; how deep could you go, and what would be the limiting factor?

No limits really. You could theoretically visit the Titanic on a rebreather if you had the right mixes. You could get down, but coming back up would be something else.

I think some COMEX divers did something close to 600 meters. I'm sure it's available on google somewhere.

X

 

[Kevrumbo]

A more insidious problem even before you get to Oxtox levels is the Dark Narc: Deep Air with increased Gas Density & Work-of-Breathing; then throw in Physical Exertion or a Stress Condition, resulting in overbreathing the regulator --all leading to the Vicious Cycle of CO2 Retention and sudden Narcosis. Can result in severe cognitive impairment at depth or worst case stupor and ultimately unconsciousness. . .

 

[Thalassamania]

What if you had a rebreather which keeps the oxygen partial pressure at a safe level, and uses helium for the diluent; how deep could you go, and what would be the limiting factor?

At that point it becomes decompression and density of the breathing media, I think heliox can go to 1500 to 2000 feet and then you start using hydrogen oxygen mixes (COMEX played with this).

 

[Belmont]

A more insidious problem even before you get to Oxtox levels is the Dark Narc: Deep Air with increased Gas Density & Work-of-Breathing; then throw in Physical Exertion or a Stress Condition, resulting in overbreathing the regulator --all leading to the Vicious Cycle of CO2 Retention and sudden Narcosis. Can result in severe cognitive impairment at depth or worst case stupor and ultimately unconsciousness. . .

Is this what happened to Dave Shaw at Bushman's Hole?

 

[hokie_diver]

At that point it becomes decompression and density of the breathing media, I think heliox can go to 1500 to 2000 feet and then you start using hydrogen oxygen mixes (COMEX played with this).

That's amazing. H2 and O2 under high pressure in a metal enclosure. Makes me nervous just thinking about it.

 

[ianr33]

That's amazing. H2 and O2 under high pressure in a metal enclosure. Makes me nervous just thinking about it.

The oxygen % used are very low though 4% ??? That makes the mixtures not explosive on the surface (and means they can only be breathed at significant depths 200+ feet ??? )

 

[Jimmer]

That's amazing. H2 and O2 under high pressure in a metal enclosure. Makes me nervous just thinking about it.

You and me both. They can't use more than 4% O2 or it will combust as is my understanding. Either way, no thanks.

 

[RS]

What is the deep record on air? 450 fsw or something like that? Gilliam or Exley???

I have nothing to add, just questions.