Why dive Deep Air?

[TMHeimer]

A while ago a trusted old freind told me that in his 20s, he and a buddy did a bounce dive on a single air tank to 200 ft. off the coast of San Diego. Said later that night his eyes burned a lot. Also, that it was the stupidest thing he's ever done. Unbelievable narcosis--he said that if they hadn't agreed to keep ONE thing only in mind--to turn around when it reads 200, they may have kept on going to China. I believe I've come across some posts on SB saying stuff like "I wouldn't go below 150 ft. on air, etc."-and some of these posts from folks who seem to have a lot of experience and pretty much seem to know what they're doing. We all know 130 ft. is the rec. limit, one which I never (intentionally) intend to go below. But other than to say "hey, guess how deep I went", are there any other reasons to do this? Got to figure that the incredibly short NDLs down there plus all the ongassing on the way down (AND up to a point) makes it awfully risky. As well, what can you do down there with about 4 minutes bottom time? I'd like to hear from those who have done this for reasons OTHER than bragging, or just to see if they could do it.

 

[Kevrumbo]

On adaptation to Deep Air and Nitrogen Narcosis:

"Moreover, our results suggest that experienced divers can discriminate between the behavioral and subjective components of narcosis. . .It has been proposed that the intensity of narcotic symptoms could be used by divers to gauge the extent of performance loss (10). The present results indicate that this advice is inappropriate for adapted divers because the two components of narcosis [behavioral and subjective] uncouple in a direction that could lead to an overestimation of performance capabilities --a potentially dangerous situation. On the other hand, the question arises as to whether adaptation confers any benefits on the diver, since performance efficiency is not directly improved and could be overestimated. In this regard, it could be argued that a reduction in symptom intensity reduces the possibility that attention will be focused on subjective sensations rather than the task at hand."
From:
p.9, Hamilton K, Laliberté MF, Fowler B. Dissociation of the behavioral and
subjective components of nitrogen narcosis and diver adaptation. Undersea Hyperb
Med. 1995 Mar;22(1):41-9. PubMed PMID: 7742709.

Deep Air along with the proper nitrox & O2 deco gases is the only other diving option if there is no helium available to blend trimix (or if helium is too economically expensive to utilize). . .

 

[vinegarbiscuit]

Reasons to do it now? No, not if you have time (and money - the training and equipment are NOT cheap) to build the experience needed to be certified as a trimix diver. But back in the day, air was all that was available, so that's what people worked with. They did staggering dives - deep dives, cold dives, cave dives, you name it - on air. Some were fortunate enough to have an extremely high resistance to narcosis and bodies that refused to tox out over the critical 218 feet mark (a tip of the hat to you here, Mr. Exley), but others didn't. Bear in mind these were not bounce dives - they were expedition dives. Divers got more than 4 minutes of bottom time, and spent a very great deal more time than that decompressing.

Today, you may see folks diving fairly deep on air. Here in Hawaii, helium and oxygen are terribly expensive and hard to obtain, so techies here will frequently make 150-200 feet dives on air and skip the expense of buying trimix (although they will use O2 mixes as decompression gases. If a pure O2 fill in a 40 cf tank can be obtained, they'll use that at 20 feet). At that level of diving, folks generally know their bodies and their susceptibility to narcosis: if they feel comfortable making such a dive on air, they will. But they'll generally draw a line for themselves: I've seen one bloke decline to deep dive here. Said he turned into a numb-nuts at anything over 150 feet, and since he couldn't afford mix, he wouldn't dive, which I reckon was a good call for him. Again - these folks aren't doing bounce dives. Most people I've seen on the boats back home in NY won't go below 100 feet without a pair of doubles and the wherewithall to handle any deco obligations that might accrue from having more gas on your back and spending more time at depth.

 

[UCFKnightDiver]

No one knows, it's pretty silly.

 

[TMHeimer]

Thanks. Those are some good answers. Even with air doubles, your bottom time must be short, but obviously better than with a single tank, like my freind had. I also didn't think of people today doing these dives as deco dives, and of course tech. divers would have all the gas knowledge needed. I guess it still has to be worth the trouble.

 

[dumpsterDiver]

Thanks. Those are some good answers. Even with air doubles, your bottom time must be short, but obviously better than with a single tank, like my freind had. I also didn't think of people today doing these dives as deco dives, and of course tech. divers would have all the gas knowledge needed. I guess it still has to be worth the trouble.

Why would you assume that people diving deep on air are not doing deco dives? Diving much past 160, and the time gets so short that you often end up with some deco, even for a short stay.

Also 218 feet isn't some kinda of terrible toxicity threshold that once crossed a diver is immediately in terrible danger. I worry more about narcosis past 220 than oxygen for a bounce dive.

 

[Dr Wu]

Once the term "bounce dive" enters the conversation you should consider another plan.

Can you do it? Sure. Should you do it? Probably not.

Ask yourself why you want to?

Do you have a good reason?

A really good reason?

 

[aquaregia]

I read in a non-authoritative source that the CNS depression from heavy (200ft+) nitrogen narcosis was known to protect against the O2 toxicity. Does anyone have a reputable source (either way) on that?

 

[TMHeimer]

Why would you assume that people diving deep on air are not doing deco dives? Diving much past 160, and the time gets so short that you often end up with some deco, even for a short stay.

Also 218 feet isn't some kinda of terrible toxicity threshold that once crossed a diver is immediately in terrible danger. I worry more about narcosis past 220 than oxygen for a bounce dive.

I assumed people were doing what my freind did- a bounce dive on one air tank., without deco. I had no idea tech. divers saved $ by using double air tanks instead of trimix, then did deco.

 

[captain]

An air deco dive with the shallow stops done on 100% oxygen is a less expensive option than trimix and O2. The new Navy rev.6 air tables has oxygen as a optional deco gas and it significantly shortens deco time..