Ascent rate

[lowviz]

I suspect that there is some truth in that. Would you ask the instructor for a reference? I'd love to have it.

The source is possibly apocryphal, have been looking for a while. Closest I ever got is a passing reference on page 180 in Dennis Graver's "100 Best Scuba Quizzes" Aqua Quest Publications, NY (1997):

Quote:
"Years ago the University of Washington did a study of recreational divers and determined an average ascent rate two to nearly four times the maximim recommended rate!"

 

[Thalassamania]

It seemed to me that Dennis often got "confused" when it came to properly crediting others, in this case I believe he should have been actually citing the same study that I did, that done by Glen Egstrom and his associates at UCLA.

 

[msg]

Sounds like a great way to get bent.

 

[Thalassamania]

There were surprisingly few bends cases, on the order of 1:10,000 which spoke I think more to the rather sparing nitrogen exposure of most divers than to good ascent technique. Coming up "to fast" is only a problem when you start to hit some of the slower compartments, you could build tables designed for a 300 fpm ascent rate ... just that the NDLs would be rather short.

 

[highdesert]

As seems to be the norm, I was in fear of my thread being hijacked. What started as a simple question on ascents quickly turned into discussions on everything but.

Sorry, but I don't quite understand your position here ...

Your opening post was quite good, and you went on to ask for others' observations. A discussion developed around your opening idea, and I was quite enjoying the posts and their relevance to your original idea. And then your follow-up (above) took me by surprise. Not to be combative, but what was it you were expecting?

 

[gcbryan]

My understanding of ascent rates is that Haldane recommended rates of 30 ft/min and less and that it wasn't until the Navy "frogmen" wanted at rate of 100 ft/min and the commercial divers wanted much less that 60 ft/min was established. Before than slower rates were used.

There doesn't seem to be anything magical about 60 ft/min. Later rates were reduced to 30 ft/min which was much like the original rates had been.

There is a study by P.B. Bennett "Rate of Ascent" revisited that showed that (using Doppler Ultrasound) there were detectable differences in bubbles upon surfacing and even more after 15 minutes between a direct ascent within the tables, a 2 min stop at 10 fsw, or a 1 min stop at 20 fsw and 4 minutes at 10 fsw.

None of the divers got bent so you can argue that some level of bubble formation is OK but given the differences in bubbles among the 3 scenarios I would certainly argue that safety stops are beneficial and should be encouraged more rather than less.

Just blindly doing a stop as if it will be the difference between getting bent or not is not the way to go but with an understanding of what's involved I can't see that safety stops are merely "gilding the lily" since it's possible that stops are the difference in many cases between "undeserved hits" or not.

I'm surprised that more doppler studies aren't done.

 

[RetMTFE]

Sorry, but I don't quite understand your position here ...

Your opening post was quite good, and you went on to ask for others' observations. A discussion developed around your opening idea, and I was quite enjoying the posts and their relevance to your original idea. And then your follow-up (above) took me by surprise. Not to be combative, but what was it you were expecting?

I asked a simple question...what are your observations and/or opinions concerning divers making quick ascents following their safety stop.
Making sure you look up when ascending and discussions on buoyancy control have nothing to do with my question.

Please explain why your only reply to the thread is one of criticism yet you say "not to be combative"? I guess I don't quite understand your position.

 

[boulderjohn]

Regardless of the history of ascent rates and safety stops, recent research indicates that safety stops may be more valuable and effective than one might think. Research is ongoing in this area. Here is an interesting recent publication from DAN:

DAN Divers Alert Network

Here is one quote from it:

What is interesting, and not necessarily intuitive, is that an in-water stop with a relatively rapid ascent rate appears to be more effective at eliminating inert gas than a very slow ascent rate. As can be seen from Table 2, a five-minute in-water stop is much more effective than simply slowing the ascent rate, even though the total ascent time is not much different (6.6 minutes vs. five minutes).

 

[Deefstes]

I asked a simple question...what are your observations and/or opinions concerning divers making quick ascents following their safety stop.
Making sure you look up when ascending and discussions on buoyancy control have nothing to do with my question.

Please explain why your only reply to the thread is one of criticism yet you say "not to be combative"? I guess I don't quite understand your position.

Good grief RetMTFE! I'll have to stick up for highdesert here. I think it is rather unfair to accuse him of being combative when he expressed his confusion with your response in a very kind way. I share his confusion but I'm worried now that I'll be labeled combative as well, specifically as I was one of the participants in the discussion (at least I thought it was a discussion) who offered observations and/or opinions.

My only conclusion is they feel, "Ok, I've done my safety stop so I'm good to go." What are your observations and/or opinions?

I asked a simple question...what are your observations and/or opinions concerning divers making quick ascents following their safety stop.
Making sure you look up when ascending and discussions on buoyancy control have nothing to do with my question.

Of course it is relevant! If a diver does not have proper buoyancy control, of course he's going to cork after his safety stop. That I would think is far more relative to your question than your own observation of "Ok, I've done my safety stop so I'm good to go". Similarly, making sure you're looking up while ascending is also something many divers don't do and as a direct result ascend too fast.

Maybe next time you'd like to include a set of rules with your post to stipulate what can be posted and what not because you've got me seriously confused here.

 

[k0rx]

Slow, slow, slow. See if you can do 3-5 minutes between the safety stop and the surface.

Dave