What's the deal with these numbers?

[diver_doug]

The recreational limit for scuba diving is 130ft. But oxygen doesn't pose a substantive toxicity issue until 218ft. BUT the record for compressed-air scuba diving is 509ft! So WTF?!?!

 

[Nemrod]

I don't follow? The 130 foot "limit" is not a law, it is simply results from a practical application of bottom time vs incurred deco (and the capacity of a typical single tank rig I might add).

The toxisity or effect of oxygen or nitrogen on individuals is rather variable and even with the same individual it can varry significantly though I do believe that some people are less prone to certain effects and can even develop a tolerence or adaptation to it.

N

 

[OneRestlessNative]

I can't answer your question but I think your signature line is pretty darn cool.....

 

[Mike Boswell]

Lots of recreational divers dive deeper than 130 feet on air. Narcosis becomes a significant factor, as does the need for stricter gas planning, time management, and problem resolution. However, IMHO, standard recreational training and equipment does not prepare or equip divers to deal with those issues.

 

[diver_doug]

I guess my point is I wonder how ambiguous these numbers are. And it's almost impossible to know just how ambiguous they are because virtually nobody pushes these so-called limits since, you know, there's that whole fear of death thing. I was just sort of thinking out loud (or typing out loud, as it were), wondering what degree of accuracy these numbers really possess. Same thing goes for the whole DCS thing. I would think all sorts of factors would come into play determining a persons "threshold" for nitrogen. E.G. I would think fit people are less succeptible than out-of-shape people, people with lots of diving experience have bodies that have "figured-out" how to dispell nitrogen more efficiently than "newb-bodies", the extent to which you're relaxed or stressed would play a role, etc. I guess I'm not really looking for an answer, I just can't help but feel that these numbers are, to a large extent, made up.

 

[spectrum]

The recreational limit for scuba diving is 130ft. But oxygen doesn't pose a substantive toxicity issue until 218ft. BUT the record for compressed-air scuba diving is 509ft! So WTF?!?!

Once you hit 130 on air you are pretty much at the end of the runway for any useful bottom time since descent is part of the burden. Multi-level benefits from a computer help a little but not significantly. In the realm of recreational diving there should be be time for some problem solving while still returning without a deco stop obligation. The "no soft overhead" / no deco element is a lynch pin of the recreational scuba definition whether there is a defacto definition or not.

Any diver is impaired at 130+ whether noticeably narc'ed or not so again we're stressing the bounds of recreational activity.

Yes, it is ~218' where oxygen concentration approaches toxic levels but susceptibility varies and if there is a problem the recovery for a recreational trained diver / team is dire. Tragic outcomes on deep air are numerous enough to speak for themselves.

The end game is safe fun and the chances of those 2 objectives plummet beyond 130' without additional training and equipment.

Pete

 

[Superlyte27]

Once you hit 130 on air you are pretty much at the end of the runway for any useful bottom time since descent is part of the burden.

Any diver is impaired at 130+ whether noticeably narc'ed or not so again we're stressing the bounds of recreational activity.

The end game is safe fun and the chances of those 2 objectives plummet beyond 130' without additional training and equipment.

Pete

Blah blah blah! Diving is different for everyone. Blanket statements like these above simply are not true for everyone.

 

[vshearer]

Yeah, lowering the BAC for driving from .10 to .08 was a ripoff too.

 

[TSandM]

Diver doug, the "numbers" on no decompression time are, at least in one sense, "made up", in that they are derived from a mathematical model of nitrogen loading and unloading that is almost certainly much simpler than what is actually going on in the human body. BUT the numbers ARE validated as the model is tested, and before the tables are released for general use. The PADI RDP, for example, has undergone extensive validation testing (our Dr. Deco was part of that). Yes, there is individual variation in DCS susceptibility -- and it may vary within the same individual from day to day, depending on conditions within the body that we don't account for in the model. The tables are created for the majority of us who fall in the middle of the bell-shaped curve.

Thus it is with oxygen toxicity as well -- the studies that have been done show a truly frightening degree of variation in threshold for toxicity between divers, and within a given diver over different dives. The recommendations for ppO2 are made based on levels where virtually NO ONE is known to have toxed, because oxygen seizures at depth are all but universally fatal.

You are free to make assumptions that you don't fall within the population for which these recommendations were written, but you have to know that you are on your own for risk assessment, once you depart from the standard recommendations.

 

[Scott L]

Thus it is with oxygen toxicity as well -- the studies that have been done show a truly frightening degree of variation in threshold for toxicity between divers, and within a given diver over different dives. The recommendations for ppO2 are made based on levels where virtually NO ONE is known to have toxed, because oxygen seizures at depth are all but universally fatal.

I am assuming this is the nearly universal PPO recommendation of 1.4? Also, what is a good comprehensive reading recommendation for oxygen toxicity issues? Thanks!