I am very new to diving, and recently I was talking to someone who has apparently been diving for quite some time. He was telling me about a cave dive that he was invloved in a few months before where he went to a depth of 300ft, and stayed for 45min. He also mentioned that it took him roughly 5 hours to decompress. I am not questioning this persons integrity, i was just wondering if someone could shed some light on how this is possible. AIR wouldn't work for obvious reasons, so is this a dive where trimix, or heliox would be used? Like i said before i am very new so there are many things i dont know, could someone please shed some light on how someone could remain underwater for that amount of time and to that depth?
Can Someone Explain?
- Thread starter kvl1027
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I dove Diepolder a couple weeks ago. 295' we did about a 30 min bottom time. Our deco was about another hour 45. I think the total time in water was 2:16. As far as the dive goes alot of us are making dives in the 200+ range on a regular basis. All it takes is a bunch of equipment which costs a bunch of money along with a bunch of training which costs a bunch of money and then you get to spend a bunch of money going on the trips to make the dives, no problem. As far as how it's done. Trimix, Nitrox and Oxygen along with a bunch of gear that costs......... well you know!
Basicly they keep you from getting stoned just breathing.kvl1027:
Gary D.
Even though you do not use "nitrox" at the deepest depths, the fundamentals are built off of nitrox training.
There are two fundamental problems with diving well in excess of 200'. First, at such deep depths nitrogen narcosis is a major problem. To help alleviate that, a gas mixture is used in which much of the nitrogen has been replaced by a gas which is less narcotic. Helium works nicely.
Second, our bodies cannot withstand atmopheric oxygen at such very high pressures. It is easiest to think in terms of oxygen partial pressure. We need somewhere between a low of about 0.16atm and a high of about 1.4atm of oxygen. Too low and you pass out, but too high and you can have a seizure.
Normal atmospheric air pressure is 1atm at sea level, and the portion of that pressure exerted by any given gas is in proportion to its abundance in the gas mixture. Thus air at the surface has a partial pressure of oxygen of 0.21atm. As you dive deeper the total pressure of the gas you breath increases to match the surrounding water pressure. At a depth of 33ft air has a ppO2 of 0.42. At a bit more than 200ft you exceed the recommended limit of 1.4atm.
Keeping the oxygen partial pressure in the right range is a function of the dive depth and the percentage of oxygen in the gas mixture. For dives which are deeper, the gas mixture is reduced in oxygen as well as nitrogen and even more helium is used.
It gets more complicated. If the gas mixture you use for the deepest depth is too low in oxygen then you cannot breath it very near the surface without the risk of losing conciousness. In these situations the technical diver will use a "travel gas" to begin descent until reaching a depth deep enough to breath a different mixture.
During ascent the diver changes gas mixtures again. At that point ridding the body of accumulated nitrogen and helium is important. This can be sped up by switching to a gas mixture higher in oxygen.
Needless to say, this is all rather complicated and not without significant risks. Those who lack proper training have no business doing these sorts of dives.
There are two fundamental problems with diving well in excess of 200'. First, at such deep depths nitrogen narcosis is a major problem. To help alleviate that, a gas mixture is used in which much of the nitrogen has been replaced by a gas which is less narcotic. Helium works nicely.
Second, our bodies cannot withstand atmopheric oxygen at such very high pressures. It is easiest to think in terms of oxygen partial pressure. We need somewhere between a low of about 0.16atm and a high of about 1.4atm of oxygen. Too low and you pass out, but too high and you can have a seizure.
Normal atmospheric air pressure is 1atm at sea level, and the portion of that pressure exerted by any given gas is in proportion to its abundance in the gas mixture. Thus air at the surface has a partial pressure of oxygen of 0.21atm. As you dive deeper the total pressure of the gas you breath increases to match the surrounding water pressure. At a depth of 33ft air has a ppO2 of 0.42. At a bit more than 200ft you exceed the recommended limit of 1.4atm.
Keeping the oxygen partial pressure in the right range is a function of the dive depth and the percentage of oxygen in the gas mixture. For dives which are deeper, the gas mixture is reduced in oxygen as well as nitrogen and even more helium is used.
It gets more complicated. If the gas mixture you use for the deepest depth is too low in oxygen then you cannot breath it very near the surface without the risk of losing conciousness. In these situations the technical diver will use a "travel gas" to begin descent until reaching a depth deep enough to breath a different mixture.
During ascent the diver changes gas mixtures again. At that point ridding the body of accumulated nitrogen and helium is important. This can be sped up by switching to a gas mixture higher in oxygen.
Needless to say, this is all rather complicated and not without significant risks. Those who lack proper training have no business doing these sorts of dives.
kvl1027:
Go back and ask your instructor why he didn't cover narcosis, oxygen toxicity, and the basic gas laws as they apply to diving adequately. All this proceeds as a logical extension of what every diver should know about these basic principles.
If an OW course is taught properly, all its graduates should need to be nitrox ready is to be shown how to use an analyzer, and told what max PPO is acceptable.
dweeb:
True, but I would hardly expect a new OW diver to be able to explain how to do a 300 ft decompression dive using hypoxic trimix.
The posters question was valid about a dive far beyond his current experience level. It would also be beyond a basic nitrox level diver, so your comments are unfounded.
MD
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