Ascending faster than 60ft/minute

[Thalassamania]

In the current PADI "Go Dive" (OW book) on page 120 it states "Swim up slowly, at a rate no faster than 18metres/60 feet per minute (slower is fine) while breathing normally"

The copyright was 1999-2004

I started my course in Aug 2005

I'm sorry, I guess I'm dense, your point is?

 

[Walter]

Once again, speed is not a relevant factor.

Yes and no. You are correct, it is the pressure change that matters. OTOH, if the diver is ascending slowly, he's more likely to remember to stop holding his breath before he kills himself than if he were moving quickly.

 

[Thalassamania]

... and if my Grandmother had two wheels she'd be a bicycle<G>.

 

[jwalko]

Wow...lots of information to absorb (no pun intended).

In these posts, the point has been made several times that evidence suggests that a relatively faster ascent from deep to a deep stop is better than a consistently slow ascent.

Alot is also referenced to the PADI open water book. keep in mind that the Open Water diver is really supposed to limit their depth to 60 feet, and only advanced open water divers should go deeper. Since I haven't taken the AOW course yet, i don't know what they teach, but i suspect more detail might be added about offgassing from deeper dives.

As to why they (the books) teach a simple ascent rate of 60 feet per minute (slower is fine/better), keep in mind that many first time students are feeling overwhelmed with all the information being thrown at them, and probably feeling intimidated by the unknown (this whole scuba diving thing...after all it is their first time). That being said, PADI probably doesn't want to throw too much information at them, such as "when coming up from a deep stop, stop at half your depth for a few minutes, then ascend even slower than you have been to your next safety stop"...too much information for an already overwhelmed student to remember. It is easier to remember to keep a slow, steady ascent. I am not arguing if it is right or wrong, just putting out a possible explination.

To me, the deep stop just makes sense. Should it be taught? Probably. is the standard OW course the right forum for it? Probably not? Will not teaching it lead to people getting injured? Who knows...one thing they hammer home in the OW course is to use common sense and not dive beyond your limits and experience...how many divers, especially new divers do that? For that matter, how many really know their limits? One thing I wish the OW course went into more detail about was what your true limits are... I felt the really important information, like this was glossed over.

Anyway, my 2 cents

John

 

[Thalassamania]

If the depth for a basic student is keep above 22 feet (which permits a direct ascent to the surface even if fully saturated), I don't give a damn what is not covered in detail.

I, for one, object to the dumbing down of scuba training programs. When I teach an entry level course it runs for 100 hours and includes 12 open water dives. There are two lectures on these topics, euphemistically titled, Problems Going Down and Problems Coming Up. All the decompression material is presented, M-Values, surfacing ratios, half-times, etc. And guess what ... people can learn it, enjoy understanding it, and are better divers for it.

Yes, SCUBA today is dumbed down. The same 100 hour course that I teach today has more similarity to the first scuba courses that were taught in the early 1950s than it does with the entry level programs being run under the auspices of most all of the agencies today. In point of fact Instructor programs today are also dumbed down and skills-made-easier descendants of that same 100 hour training program.

Oh, BTW: individuals that have completed the kind of program described above are considered to be ready and qualified to dive without supervision to a depth of 30 feet. Now perhaps you can see why the current state of training and diver knowledge gives me the willies.

 

[jwalko]

I, for one, object to the dumbing down of scuba training programs. When I teach an entry level course it runs for 100 hours and includes 12 open water dives. There are two lectures on these topics, euphemistically titled, Problems Going Down and Problems Coming Up. All the decompression material is presented, M-Values, surfacing ratios, half-times, etc. And guess what ... people can learn it, enjoy understanding it, and are better divers for it.

I agree. However, both in the OW course and during the OW dives afterwards (I did each w/ a different dive shop in different locations), you would not believe how many people just didn't get it. You would think many of then had never been in the water before. I had my 11 year old daughter w/ me (getting her junior OW) and she understood it better than many of the adults.

And, we also had students who just didn't listen. We had one guy who just couldn't stay with the group...no matter how many times the DM said stay close, there he was swiming all over creation, zig-zagging back and forth and hoovering air like there was no tomorrow. Hmmm...maybe there shouldn't be an automatic passing grade just because you demonstrate you can do the skills...but I guess that is a topic for a completely different dicussion.

John

 

[rjpv]

Thanks for all the replies!

I guess my "real" question is relative risk of DCS. Obviously precise risk is dictated by secondary risk factors and details, but...

If I make a controlled emergency swimming ascent from 30 feet for 30 minutes, am I definitely going to get the bends? While I get DCS half the time? Same question for ascending at, say 80ft/min.

And an unrelated question: reading the boards it sounds like it is possible to have a mild case of DCS and simply not notice (ie, mild joint soreness and fatigue are pretty vague symptoms). If this is the case, is medical treatment required or will things resolve spontaneously over time?

I'm a little worried that I will accidentally ascend at 70ft/min, have a sore shoulder from lugging scuba gear around the beach and not know if I need to run off to a recompression chamber "just in case".

 

[Charlie99]

I guess my "real" question is relative risk of DCS. Obviously precise risk is dictated by secondary risk factors and details, but...

If I make a controlled emergency swimming ascent from 30 feet for 30 minutes, am I definitely going to get the bends? While I get DCS half the time? Same question for ascending at, say 80ft/min.

.....

I'm a little worried that I will accidentally ascend at 70ft/min, have a sore shoulder from lugging scuba gear around the beach and not know if I need to run off to a recompression chamber "just in case".

The risks of severe DCS increase rather slowly. For many years, the standard dive table was the US Navy table. A typical no-deco limit was 80' for 40 minutes, with a direct ascent to the surface at 60fpm. If you take any of todays computers down to 80' for 40 minutes (on air) and you will be in decompression.

Popping up to the surface at 70fpm is kind of like not wearing a seat belt while riding in a car without airbags. It is clearly not as safe as being belted into a car with airbags, but OTOH, it doesn't mean that every time you don't wear a seat belt that you are going to be killed. You are taking more risk without the seat belt, but it is still far more likely that you will survive the trip than you will be killed.

Is a fast ascent risky? Yes. But even if it increases the risk by 10 times, then you are looking at a DCS risk of 1 in 1000, rather than 1 in 10,000.

If you search around Scubaboard, you will find various discussions about whether or not it is wise to descend back to depth if you have done an uncontrolled ascent. IMO, it's a case of balancing the risks. If you are with your buddy, or he is watching you from below, you have enough air, and have regained control of your emotions and are calm, the go ahead and descend. If you are freaked out, then the risk of having additional problems probably outweighs the advantages of going back down, and it is best to stay on the surface. If you have even the slightest hint of DCS / medical problem, then stay on the surface.

 

[immersed]

Not to be a stickler for exactness, but given that the topic is one that can affect people's lives

especially as concerns the behavior of gas once it changes phase

The gases you breathe don't change phase unless you're lowering your body temperature a couple hundred degrees - or 'deep dive' means several miles.

Bottom line: 3 minutes at 1/1 you max depth

1/2

So what you want to do is keep the nitrogen in your body just below the level of bubbling off and thus have maximum driving force for offgassing while NOT forming bubbles.

My understanding of microbubble theory (and to my knowledge it hasn't been disproven) is that bubbles are there, and the point is to keep them small enough to be harmless.

I know that when I taught my OW students that the rule was Don't Ascend Faster than 60ft/18m per minute. Slower is always better. I used to tell all my students that the last 33ft. is where the Dysbarism changes the greatest and will do the most damage. ~Cheers~

No! Ascent rate has nothing to do with Arterial Gas Embolism (AGE) if you hold your breath and ascend, regardless of speed, you will pop a lung eventualy. Rocketing to the surface makes an AGE more likely due to the surrounding situation, but is NOT THE CAUSE.

FyshEye did not assert that it was. And actually, if we're being exact, if I hold my breath and ascend 3 feet, I'm not going to pop a lung - no eventually about it.

#75

Off topic


I agree with the gist of Thalassamania's message. I ascend at 30 ft/min and most of my dives are to 40 feet or less, so I don't do a stop halfway - however, I am cognisant of the recommendation and will apply it as necessary. I, as a diver of a whole 4 years and 60+ dives, wholeheartedly proclaim that I am not qualified to debate Thalassamania or many other SB members on dive matters. It's obvious that Thalassamania has done extensive research on nitrogen theory. However (you knew that was coming), I would like to point out that it is theory, and it could change next year. Dr. John Scott Haldane's experiments were performed on goats a hundred years ago and a lot of people have studied it an awful lot since then, but it's still theory. Until someone wants to experiment on a few thousand humans, it will continue to be theory (and then it will elevate all the way to medical science oboy). Maybe I'm the only one who interprets it this way, but it appears to me that all of the paragraphs that Thalassamania has typed and pasted are being presented as cold hard facts, and fact is, they aren't. Good example:

super saturation ratio is exceeded and thus bubbling occurs causes DCS

The scientists have an important word in their text: "potential DCS".
Look at the language used in the DAN article quoted in #67 - "appears to be more effective", "It would seem from"

Believe it or not, I'm not picking on Thalassamania. I'm not. I am calling him on exactness since he's doing that to others, but that's as far as it goes - as I said, I agree. My point here is that you can't pin a scientist down on anything, especially human physiology, and it appears to me that Thalassamania is giving them more credence than they're willing to assign to themselves. Really, the answer to the original question is "well, either nothing or you'll die, or something in between". Bottom line is you can only do what you can do: stay hydrated, in good physical shape, dive within the established NDL limits (which are just educated guesses and guarantee nothing), don't over-exert yourself, and pick your favorite theory for ascents. Do all that and you can still get bent.

 

[Fireman Ken]

Air embolisms in the lungs could occur if you hold your breathe while surfacing. As the pressure decreases while you rise, air expands (Boyles Law) and the air has to go somewhere. Ascent rate deals directly with DCS.

Ken