How much oxygen is there...

I do a fair bit of tech diving and a number of my friends are getting into re-breathers. I just can't - they completely give me the heeby jeebies.

CO2 poisoning is a weird way to go. You slow down, you don't realise there's a problem... Under 30-40-50m+ of water that's an issue.

Recreational scuba on Air is usually on 12 litre tanks roughly 21.x% oxygen, usually at around 220bar at surface temperatures (fill anyway, depends where you are obviously). 220bar in a 12l is 2640 litres of air.

As people have already mentioned, oxygen gets toxic if you go deeper - it's to do with partial pressure. For air the stated limits are around 1.6PPO which is, I think from memory, around 55m. Beyond that depth you need to switch to trimix (heliox and the like). Yes, it makes you talk funny.

You can use enriched air (Nitrox) for shallower dives and it reduces your intake of Nitrogen. Depending on your skills you either use it to extend your bottom time (ooer) or to make your existing dive safer.

That James Bond clip with the thing in his mouth - bull really isn't it? Air has volume - how can you create volume from such a small space?
 
I did see something about a lab trying to extract breathable air from sea water, which may be what Bond had, however, the process needed a lot of power and was huge...
 
Would be a horrible experience breathing in liquid for the first time though. And i assume youd have to cough it all up as well :\
 
SideWinder said:
Inspiration = That James Bond film where James has that tiny thing on his mouth that means he can be under water for a while.

In a standard scuba diving tank, how much oxygen is there? How much could Bond's hold in theory?

Yes i can't sleep. :(
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not sure if it's been answered but a standard scuba cylinder of 12litres @ 232bar contains 2784litres of air, air contains roughly 80% nitrogen and 20% oxygen so the tank would contain 557litres of oxygen

the consumption of the air is greater the deeper you go so the deeper you go the less time can be spent
 
As people have already mentioned, oxygen gets toxic if you go deeper - it's to do with partial pressure. For air the stated limits are around 1.6PPO which is, I think from memory, around 55m. Beyond that depth you need to switch to trimix (heliox and the like). Yes, it makes you talk funny.
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it's not a depth as such as it would be dependent on the mixture involved , more oxygen content = higher ppo2 at less depth

a 20/80 mix would give

ppo2 0.4 at 10 metres
ppo2 0.6 at 20 metres
ppo2 0.8 at 30 metres
ppo2 1.0 at 40 metres
ppo2 1.2 at 50 metres
ppo2 1.4 at 60 metres
ppo2 1.6 at 70 metres

iirc with the standard mix at over 0.6 it starts become toxic with minor symptoms with 1.4 or 60 metres as the recommended limit where it becomes poisonous, 1.6 being the absolute maximum

Anyone going to 60m on a standard mix must be nuts tbh lol
 
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Been to 55m on air in Scotland on the Rondo...
It was more of a spike to that depth than actually finning around down there though as the wreck sits almost vertically on a cliff face.
Water was dirty, it was dark, water was freezing cold, tide wasn't slack. probably the worst set of conditions to do a deep dive in. :-/
(twin 12's @ 230bar)
****ing fantastic dive. ;)

No need to flap at the instructor about taking your GF to 60m, He stayed within the 1.6ppo max and probably didn't stay down at that depth a minute longer than necessary.
It's not just simply exceeding the 1.6ppo and you die instantly, it's about how much abuse your central nervous system can take. 80% total exposure being the recommended max.
The tables say you can stay at 66m on air for 45mins before reaching an 80% loading of your CNS...
The decompressions stops for that dive wouldn't be fun though. :o
 
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Rebreathers scare the **** out of me.

I was pool training with my uni club a few years ago when a friend of a member came to 'try out his new rebreather'.

The tit forgot to turn on the O2 and proceeded to pass out at the bottom of the 4m high-dive plunge pool.

Cue a real-life rescue by four or five of us.

I realise this was user error more than the rebreather itself but at least if you forget to turn on a standard cylinder you know about it pretty quickly.

Due to the residual O2 in the loop he wasn't aware of his mistake until it was too late.
 
One failing of the human body.. If it's breathing it thinks its OK.
There are no internal sensors to say "ABORT ABORT, NO OXYGEN COMING IN CAPTAIN"

Which goes back to the previous question about breathing liquids..
The body isn't designed not to breathe. (yes it can be trained, free divers are testament to that)
 
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Scubascorpion said:
No need to flap at the instructor about taking your GF to 60m
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Look, i know you know about diving and whatever, but that doesnt mean you can write off the severity of the situation.

There was no reason to go to 60m, it was deep blue. There was nothing to look at but a further mile of descent. She was inexperienced, and admitted she panicked when she read the depth on the Suunto. Clearly you understand what happens when you panic, so there's no need to go over that. I and my buddy were almost 300m away, where we had agreed to dive.

I understand the concept, and wasn't concerned about my girlfriend becoming instagibbed (in hindsight it would have saved me 5 years of misery). The point was when you put your life in the hands of someone, they should be aware of responsibility. Finning off to 60m with an inexperienced diver just because its "cool and dark" is something I would empathise with people flapping about.

Didn't stop her becoming an instructor over the course of the next 3 years, which is something to be thankful for.
 
The small emergency hybrid rebreathers that you get for going offshore can last a couple of minutes if you're lucky (the chopper doesn't actually sink).
 
60 metres is a silly depth to take someone with little experience at deep diving, it's something that should be done gradually , there's a whole manner of things that could go wrong and the chances of narcosis is very high. The instructor was stupid imo and your ex should've told him not to go deeper or thumbed the dive, but of course if she was already slightly narced she may have been totally willing to go deeper, something a good instructor should have realised
 
It depends on other conditions too, if the waters were warm, the visibility was good, the current was slack and you had a good reference points then the chances of being narced are highly reduced.
She's gone on to become an instructor FFS, she must have loved it :D
 
My understanding is that none of those have a lot to do with narcosis, they will however make the dive less stressful and less chance of panic, narcosis can happen at any depth but >30m the risk of it is greatly increased no matter what the conditions are, hence people should be broken in so they can get used to knowing if they are getting narced and take apropriate action.

Ayways you will already know all of that, but my opinion still stands the instructor was risking someones life taking them to such depths without a dive plan, prior experience of the buddy
 
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If you are relaxed and not exerting yourself you wont be sucking on the gas like a crazed gibbon so it has a very big effect on narcosis.

OK, I've got the books out now, be warned. :D

Technical Diving International - Extended range manual.

1. Narcosis is a mood enhancer and irrevocably intertwined with stress. The more things that stress you on a dive, the more "narked" you become.

2. Reduce all effort at depth to a minimum to reduce the inert gas concentration in your tissues. The harder you work and the heavier you breathe, the more narcosis will affect you
 
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60m not a problem? Seriously? For an inexperienced diver? By inexperienced I assume then she was diving on a single 12 or 15litre tank?

Taking somebody to that depth on recreational gear is simply ridiculous. I've done probably 2.5k dives now and the only way I'd go that deep is with a tech setup.
 
I remember years ago doing the PADI advanced thingy where you test the effects of narcosis by doing puzzles and answering a few questions (on a slate, obviously) at 30 metres.

One of the questions was 'Name an animal beginning with 'N'. Had me completely bloody stumped - on land too :D Eventually came up with Newt.

I do not believe that was a fair test :p
 
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