When is it okay to exceeding training limits?

[Basking Ridge Diver]

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[boulderjohn]

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Here is a Wikipedia summary: Dive computer - Wikipedia, the free encyclopedia

 

[Omisson]

Done and done - you are correct - so the question is how closely does V-Planner match DSAT or PZ+ - is it close? Deep stops seem to bring the deco obligation down but do not eliminate the obligation.

Whether Deep stops help or hurt deco and DCS incidents is a whole nother thread raging elsewhere on scubabboard....

MANY hyperbaric experts since 2008 seem to point to the studies that suggest they are not helpful.... again another thread...

 

[NAM001]

I believe there are physics involved in the 130. Certainly narcosis is a physics issue. I believe that issue has a wide range of answers however if you toss out the extreems of like 40 feet and a million feet i think most will agree that you can dive safely to 130 with out serious imparement at 130 with even lesss risk at <100 ft. Then there is how long will your tank last at 130 and allow you to get up again. So you are at 5 atm and you have a bad sac of 1 so you have just over 10 min of air at 5atm. couple that with ndl limits and the 2 will push you shallower and give you more air time. Any pushing beyond 100-130 i think all will agree starts to require more skills to deal with those taught for ow-aow depths. It no longer remains stupid proof and there fore exits the recreational relm of diving. kind of like going from a autmatic to a stick with multispeed rearends. computer wise it is no longer plug and play. There are those who do bounce dives to 200' on al80's of air, but i dont count that as diving. So i guess that is a magic depth that with the basic skills and basic single tank rigs you cant exceed without running out of gas with minimal risk. your reference to ean32 is just a complicating factor that changes the rules because you are introducing an additional limiting factor. That being PPO2. What if youare using ean40 ir Ean 27. the O2 related limits change. Your specific reference to ean32 i think is because everyone talks abour 32, probably because it fits with in the preexisting physics limitations already present with air diving. You hit the nail on the head when you said richest mix for rec limits. And those limits are air limits. Its very clear to me by your posts that you are analyzing the info cause you seam to be coming up with the responsible conclusions. You have the right mindset needed to unserstand the more advanced training areas involved. I hope ou persue whose paths when you find yourself ready.

And here I was thinking that 130' was tied somehow to the physics of O2. I do like to make stuff up...

I was thinking that it was somehow related to the MOD of EAN32 being 40m (for 1.6ATA ppO2).

Now, don't ask me why I would think that instead of, say, using the MOD of EAN30 or even EAN28 or less. Or, really, why anyone would use any of those over the MOD of air, if that's what they were using to decide the safe limit for Rec diving....

Now that I think about it more, I suppose it's more likely that EAN32 has become the most common blend of Nitrox because it's the richest blend you can use at any Rec depth. So, max depth implied Nitrox blend, rather than the reverse.

And, looking at the NOAA NDL table for air, I see that you only get 10 minutes at 130'. Maybe somebody decided there was not much point in diving deeper than that, since you wouldn't even be able to stay 10 minutes, so they made that the limit. Which I guess is just another way of saying what boulderjohn said. Past 130 (on air), you're pretty quickly into mandatory deco dives, right?

 

[Bob DBF]

When I first started diving, the recreational limit was 190' or so I was told. It basically was the limit because 200' had no NDL time. You had 5 min at 140' to 190' so you had to drop fast and do whatever quickly, and you sure had no time to be narked. These depths were not usually done as NDL dives because of the short bottom time and the chance that narcosis could slow you down. Ascent was 60'/min to the surface.

Not that I had anything to do with it, but the limit was set to 130' probably because of narcosis, as boulderjohn mentioned, and the NDL time at 130' was 10 min which was not nearly limiting as diving deeper. I don't think anyone noticed the change at the time, I didn't.



Bob
------------
I may be old, but I'm not dead yet

 

[scagrotto]

I claim we need to appeal to the language police to figure this out once and for all. ...
Many people focus on the phrase "training AND experience" as opposed to the phrase "training OR experience".

As a duly licensed member of the language police, I submit that "training and experience" is a single thing. It's the sum of your training and your experience. If you've got an OW cert that never took you deeper than 40' in clear calm water, and you've now racked up 50 dives, including a bunch to 100', than you've definitely got "training and experience" that exceeds your OW cert.

Scuba police or not, I'd be checking the wording of my insurance policy before exceeding PADI's 60' limit.

I think one of the things that's clear from this thread is that there is no 60' limit:

verbatim from the Open Water Manual (p. 235):' ... Ultimately it is your responsibility to set your limits for each dive based on your assessment of your skills, comfort level and the dive conditions.'

I've heard that a lot of health policies have very poor coverage for chamber rides, but I've never seen anything that limits the coverage based on your certification. Of course, that's not to say that an insurance policy doesn't have some kind of clause designed to give the insurance company a get out of jail free card. It's well known that health insurers pay fat bonuses to employees whose job is to find the reason for denying coverage.

Plus, as you ascend and the ambient pressure drops, some of the air in your "empty" tank will become available, right?

That's the reason you keep the reg in your mouth as you ascend and exhale. If your empty tank is an AL80 it's got an actual interior volume of about 0.4CF. At the surface it will actually contain 0.4CF that you won't get out of it without using a vacuum pump. 132' is 5 ATA, so the empty tank contains about 2 CF, or about 1.6CF that becomes available as ambient drops to 1 ATA. Ascending to 99' will free up 1 ATM, or about 0.4CF. Ascending to 66' frees up another 0.4 CF, and so on. In theory you'll be able to breathe that as you ascend. In reality, the small difference between the tank pressure and ambient pressure means the air isn't going to come rushing out the way it did when the first stage was delivering air at 140 psi over ambient. Of course you would have had a similar limitation when you took that last breath at 132', so getting a breath at 99' shouldn't be any harder than the one before.

My only real life experience with running OOA was deliberate while laying on the sand in 3' of water. As I recall, my last breath may not have been delivered very quickly, but it wasn't overly slow and it wasn't difficult. That makes me pretty confident that an empty tank would give me a half dozen breaths during an ascent from 130ish. That's not a lot, but it's way better than zero.

This is the problem of "shallow water blackout"

Every cloud has a silver lining. If you're going to drown anyway, being unconscious is going to make it a more pleasant experience.

descent time doe not appear to impact my dive time... Am I imagining that?

I see that you already checked with a computer, but I'm sure you can answer this question:. Do you ongas anything at all during the descent, or does ongassing only start when you stop descending? The only real question is exactly how much of your 5 to 10 minutes of NDL are lost to the descent. Of course you're probably going to make a lengthy deco stop if there's something to see between 60' and the surface, so even if you didn't account for losing a minute because of the descent it probably won't matter.

 

[scubadada]

I don't know. My main point was that as you increase the depth and decrease the total bottom time, the descent rate becomes increasingly important in relation to total bottom time.

Here is a 10 year old study you might find interesting. It is a comparison of the algorithms used in dive computers of that day. It is interesting because it shows how very different the algorithms we use are, and it therefore shows how far off we are from having this whole thing nailed down.

Hi John,

This is an abstract from the UHMS meeting. Do you know if the study was published as a full paper, I would love to see the detailed results. The Wikipedia summary is inadequate

Good diving, Craig

 

[Basking Ridge Diver]

Every cloud has a silver lining. If you're going to drown anyway, being unconscious is going to make it a more pleasant experience.

I see that you already checked with a computer, but I'm sure you can answer this question:. Do you ongas anything at all during the descent, or does ongassing only start when you stop descending? The only real question is exactly how much of your 5 to 10 minutes of NDL are lost to the descent. Of course you're probably going to make a lengthy deco stop if there's something to see between 60' and the surface, so even if you didn't account for losing a minute because of the descent it probably won't matter.

I am told by someone that had gone through it - once you reside yourself to the fact you are going to drown - it is very peaceful almost serene - very much like diving. (And of course as he was laying there resigned - he was pulled out of the water and told me this story.)

Well - the real answer is yes you will be on-gassing - the question is how much?

However - I asked a question on a different thread but in the opposite way - is it time or breathing on your safety stop that off gasses? The answer was curious - so it is not just time - your breathing does impact your on gassing - since that is where the nitrogen is coming from for your Deco Obligation. So my thought is I am not equally breathing every foot or so when I am descending at greater than 60 fpm. My thought process would say - perhaps it is every 5 to 8 feet I am breathing in and out - I do the head down descent. That leads me to believe that I would on-gas less than the full amount that V-Planner is accounting for and attributes to my descent. But that is my hypothesis - am I way off?

 

[rhwestfall]

Please keep in mind that the models are just a conversion of statistical analysis, and a SWAG at what is happening..... we really aren't sure what is happening to our bodies, or that we can accurately create a calculation/model that truly includes all the necessary elements. This has been proven by folks "doing it right" (no, not that kind), and still getting a visit to the chamber....

The limits are realistically quite blurred, so deciding to approach them entails elevated risk....

 

[stuartv]

This will all be moot after Samsung releases the Galaxy S9 Pro Plus, waterproof to 200 meters and with built-in blood and 16 compartment micro-bubble sensor.