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I'm am proud to be included in what I know to be a group of honorable and smart people. My sincerest thanks.
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This message is hidden because DwayneJ is on your ignore list.
No question that deco is theory, but please consider the following, from the DAN website (citation below):
British physiologist Sir Leonard Hill theorized that decompression should be by linear ascent to the surface; he strongly disagreed with Haldane's approach. However, in the end Haldane was able to prove, using goats, that a slow linear ascent was not only ineffective, but unsafe; too much nitrogen remained on surfacing resulting in frequent DCS.
Full article is available at DAN.
-Bryan
Interestingly, however, these articles also point out that current no-decompression recreational dive tables and computers -- which also have lots of data to support them -- actually follow Hill's model more closely by stressing slow ascents and only requiring safety stops when one comes within 3 pressure groups of a no-decompression limit, etc.
I'm having a problem with terminology. Specifically the terms "no-decompression recreational diving", "safety stop" and "no-decompression limit".
I thought no-decompression recreational diving using tables had, as a fundamental premise, the ability to make a no-stop ascent to the surface at any time within the NDL. Further, I thought the allowable ascent rate was 60 fpm, not 30 fpm.
I thought the safety stops were recommended as opposed to required. Because, it seem to me, if they are required, they are decompression stops and this is no longer a no-decompression recreational dive.
I'm not suggesting that the safety stops be ignored nor am I suggesting that a slower ascent rate isn't helpful for recreational diving. What I am trying to do is sort out the terminology: is the safety stop actually required (within 3 letter groups for PADI) or is it just highly recommended?
Is the 30 fpm ascent rate a good idea or is it fundamental to using the tables? Actually, I know the answer to this one: the PADI tables indicate a 60 fpm ascent rate as does their training literature. Same for NAUI.
One final concern: when a computer indicates an NDL, do they really mean no-decompression limit? Can I directly ascend to the surface within that NDL?
Richard
However, the OP's question and others' subsequent replies left me wondering:
Does a slow, linear ascent not work because linear ascents never work, or is it just that we simply haven't found the right ascent rate yet? Might a sufficiently long ascent work just as well?
If not, then why not? What is going on physiologically that prevents a slow, linear ascent from working?
If we had no other information besides the goats, this would be a reasonable question. But we now have voluminous studies, including Doppler measurements of actual bubbles in the blood stream. The goats were early data, and useful, though leaving the possibility of the above unlikely flaw. As with all theories, the more confirming data we have, the less likely such alternate explanations become.... By the way, did anyone ever wonder whether Haldane was better than Hill at picking healthy goats?
Here's how I read the terminology and recommendations:I'm having a problem with terminology. Specifically the terms "no-decompression recreational diving", "safety stop" and "no-decompression limit".
I thought no-decompression recreational diving using tables had, as a fundamental premise, the ability to make a no-stop ascent to the surface at any time within the NDL. Further, I thought the allowable ascent rate was 60 fpm, not 30 fpm.
I thought the safety stops were recommended as opposed to required. Because, it seem to me, if they are required, they are decompression stops and this is no longer a no-decompression recreational dive.
I'm not suggesting that the safety stops be ignored nor am I suggesting that a slower ascent rate isn't helpful for recreational diving. What I am trying to do is sort out the terminology: is the safety stop actually required (within 3 letter groups for PADI) or is it just highly recommended?
Is the 30 fpm ascent rate a good idea or is it fundamental to using the tables? Actually, I know the answer to this one: the PADI tables indicate a 60 fpm ascent rate as does their training literature. Same for NAUI.
One final concern: when a computer indicates an NDL, do they really mean no-decompression limit? Can I directly ascend to the surface within that NDL?
Richard
Is the 30 fpm ascent rate a good idea or is it fundamental to using the tables? Actually, I know the answer to this one: the PADI tables indicate a 60 fpm ascent rate as does their training literature. Same for NAUI.
This is, as you said, a terminology issue. It took me some time to realize that "decompression" is used in two different ways, as I now point out to new dive leaders.I'm having a problem with terminology. Specifically the terms "no-decompression recreational diving", "safety stop" and "no-decompression limit".
[snip]
I thought the safety stops were recommended as opposed to required. Because, it seems to me, if they are required, they are decompression stops and this is no longer a no-decompression recreational dive.