Average depth finder

[Basking Ridge Diver]

Here is the post written by everyone's beloved TsandM (Lynn Flaherty). May her soul rest in peace ...

No disrespect intended but you are using an 8 year old thread to determine what is best for you?

I think Lynne would acknowledge a whole lot has happened in the last 8 years and you may want to consider that before you go head long into the abyss.

I applaud you for checking it out on a few dives with the safety of a DC but if you are serious about deco - I am not sure this is the right long term solution.
Good luck!

 

[CAPTAIN SINBAD]

I would suggest there are a lot more people that dive by following their computers with an excellent safety record.

I am not too sure about that. The whole problem with decompression sickness is that its symptoms can range from very every other day things like lethargy, fatigue, itching and headaches to some very unusual things like paralysis and death. You can put all sorts of things in between like numbing and pain in joints and inability to breath etc.

I am convinced that a lot of people who religiously follow their computers are leaving the water pretty bent and out of shape. Yet because they are within the NDL numbers generated by their dive computers, they do not realize that they are bent. The only time they do not feel the post-dive lethargy (very common symptom of a Type 1 hit) is when they are on Nitrox and diving the same profile that they always dove on air. Then, when they are sitting on the boat after the dive without lethargy they always felt, they think that Nitrox has some magical property that it is makes them feel energetic! It never occurs to them that it is not nitrox that is giving them this newly discovered energy. It is the simple fact that the air that they were on was bending them out of shape while their computer was still showing them that they are within NDL.

Every time you come across someone who tells you that they feel so much better on nitrox, you can pretty much bet your life that the guy was getting bent on air but never realized it because he was watching his computer. In my experience, it is always the older divers who make this claim about Nitrox and its magical properties because this demographic is more susceptible to DCS. I have yet to find a 22 year old who will tell me that nitrox makes him feel better and more energetic after a dive. The US Navy table air table was designed for this dude so he will be fine.

When this older crowd (such as Lynn herself) switch to the UTD/GUE ascent then they feel that breathing air generates a post dive feeling that is similar to breathing nitrox because the post dive symptoms of fatigue they always felt are not there any more.

While I am extremely concerned about the folks who got bent doing Ratio Deco, I am equally concerned about the "computer chaser" who will get bent a hundred times in his life but never realize it because his computer does not tell him that he is bent.

I know such a person. Every time she is on a boat, she takes headache medications along with sea sickness meds because she "always gets a headache after a dive and feels like sleeping" (Type 1 hit). When the dive is over and the boat is returning, it would be a two hour trip back to Morehead city NC. You will always find her sleeping on the dining table with headache meds and it would be pretty hard to wake her up. Since a whole bunch of people use those tables to "crash after a dive" such behavior has become an accepted part of NC diving. Try convincing her or any of these others "sleepers most of whom would be with headache meds" that they are experiencing a type 1 decompression hit and they will pull out her Suunto and tell you "I use my computer and I always dive safe!"

Decompression is not an exact science and when you build precision devices to measure something you have not really defined, then you start an era of "computerized stupidity." Whether UTD and its Minimum Decompression is the best way to solve this, is something I am not sure yet. It is an option that was built to address this flaw so lets give it a shot and see what happens?

 

[scubadada]

I am not too sure about that. The whole problem with decompression sickness is that its symptoms can range from very every other day things like lethargy, fatigue, itching and headaches to some very unusual things like paralysis and death. You can put all sorts of things in between like numbing and pain in joints and inability to breath etc.

I am convinced that a lot of people who religiously follow their computers are leaving the water pretty bent and out of shape. Yet because they are within the NDL numbers generated by their dive computers, they do not realize that they are bent. The only time they do not feel the post-dive lethargy (very common symptom of a Type 1 hit) is when they are on Nitrox and diving the same profile that they always dove on air. Then, when they are sitting on the boat after the dive without lethargy they always felt, they think that Nitrox has some magical property that it is makes them feel energetic! It never occurs to them that it is not nitrox that is giving them this newly discovered energy. It is the simple fact that the air that they were on was bending them out of shape while their computer was still showing them that they are within NDL.

Every time you come across someone who tells you that they feel so much better on nitrox, you can pretty much bet your life that the guy was getting bent on air but never realized it because he was watching his computer. In my experience, it is always the older divers who make this claim about Nitrox and its magical properties because this demographic is more susceptible to DCS. I have yet to find a 22 year old who will tell me that nitrox makes him feel better and more energetic after a dive. The US Navy table air table was designed for this dude so he will be fine.

When this older crowd (such as Lynn herself) switch to the UTD/GUE ascent then they feel that breathing air generates a post dive feeling that is similar to breathing nitrox because the post dive symptoms of fatigue they always felt are not there any more.

While I am extremely concerned about the folks who got bent doing Ratio Deco, I am equally concerned about the "computer chaser" who will get bent a hundred times in his life but never realize it because his computer does not tell him that he is bent.

I know such a person. Every time she is on a boat, she takes headache medications along with sea sickness meds because she "always gets a headache after a dive and feels like sleeping" (Type 1 hit). When the dive is over and the boat is returning, it would be a two hour trip back to Morehead city NC. You will always find her sleeping on the dining table with headache meds and it would be pretty hard to wake her up. Since a whole bunch of people use those tables to "crash after a dive" such behavior has become an accepted part of NC diving. Try convincing her or any of these others "sleepers most of whom would be with headache meds" that they are experiencing a type 1 decompression hit and they will pull out her Suunto and tell you "I use my computer and I always dive safe!"

Personally, I think you have some significant misconceptions regarding decompression and decompression sickness.

Best of luck, I will use my computers to judge NDLs and the need for obligatory deco stops

 

[JohnN]

I am not too sure about that. The whole problem with decompression sickness is that its symptoms can range from very every other day things like lethargy, fatigue, itching and headaches to some very unusual things like paralysis and death. You can put all sorts of things in between like numbing and pain in joints and inability to breath etc.

I am convinced that a lot of people who religiously follow their computers are leaving the water pretty bent and out of shape. Yet because they are within the NDL numbers generated by their dive computers, they do not realize that they are bent. The only time they do not feel the post-dive lethargy (very common symptom of a Type 1 hit) is when they are on Nitrox and diving the same profile that they always dove on air. Then, when they are sitting on the boat after the dive without lethargy they always felt, they think that Nitrox has some magical property that it is makes them feel energetic! It never occurs to them that it is not nitrox that is giving them this newly discovered energy. It is the simple fact that the air that they were on was bending them out of shape while their computer was still showing them that they are within NDL.

Every time you come across someone who tells you that they feel so much better on nitrox, you can pretty much bet your life that the guy was getting bent on air but never realized it because he was watching his computer. In my experience, it is always the older divers who make this claim about Nitrox and its magical properties because this demographic is more susceptible to DCS. I have yet to find a 22 year old who will tell me that nitrox makes him feel better and more energetic after a dive. The US Navy table air table was designed for this dude so he will be fine.

When this older crowd (such as Lynn herself) switch to the UTD/GUE ascent then they feel that breathing air generates a post dive feeling that is similar to breathing nitrox because the post dive symptoms of fatigue they always felt are not there any more.

While I am extremely concerned about the folks who got bent doing Ratio Deco, I am equally concerned about the "computer chaser" who will get bent a hundred times in his life but never realize it because his computer does not tell him that he is bent.

I know such a person. Every time she is on a boat, she takes headache medications along with sea sickness meds because she "always gets a headache after a dive and feels like sleeping" (Type 1 hit). When the dive is over and the boat is returning, it would be a two hour trip back to Morehead city NC. You will always find her sleeping on the dining table with headache meds and it would be pretty hard to wake her up. Since a whole bunch of people use those tables to "crash after a dive" such behavior has become an accepted part of NC diving. Try convincing her or any of these others "sleepers most of whom would be with headache meds" that they are experiencing a type 1 decompression hit and they will pull out her Suunto and tell you "I use my computer and I always dive safe!"

Decompression is not an exact science and when you build precision devices to measure something you have not really defined, then you start an era of "computerized stupidity." Whether UTD and its Minimum Decompression is the best way to solve this, is something I am not sure yet. It is an option that was built to address this flaw so lets give it a shot and see what happens?

You seem to have defined DCS in a manner in a way that it supports your position. Rather circular logic, isn't it? I'm unaware of any empirical evidence that would support your position that following a DC algorithm (whatever it might be) increases the likelihood of a DCS hit over ratio deco?

If you like I could dig out the Jaworski anti-computer rant to see one of the set of assumptions behind ratio deco. . .

 

[tbone1004]

Personally, I think you have some significant misconceptions regarding decompression and decompression sickness.

Best of luck, I will use my computers to judge NDLs and the need for obligatory deco stops

holy sh!t we agreed on something! write this down in the record books!

@CAPTAIN SINBAD I would highly recommend you also read the amount of incidents that AG's deco recommendations and VPM have bent people like pretzels... AG has a very lucky ability to offgas more efficiently than most people so what works for him is fine, but not necessarily transferrable. I would urge you to read the latest research and recommendations on deco profiles, and I think you'll find that a lot of it is not in line with what is used by UTD and even GUE anymore who still favor deeper stops *GUE I think roughly correlates to 30/85? someone please confirm*, but lots of research is indicating getting shallower faster with a gf-lo around 50 or higher

 

[boulderjohn]

Here is the post written by everyone's beloved TsandM (Lynn Flaherty). May her soul rest in peace ...

Lynne was a friend of mine. We did a number of dives together, and we had a number of online discussions about deco theory. I find it interesting in relation to what we discussed together and what we know about decompression theory now. Let's take a look at some of what you quoted.

"The concept of "minimum deco" comes from the idea that there really is no such thing as a "no decompression" dive. ALL dives involve absorption of nitrogen, and offgassing or decompression. "No deco" dives are the ones where the M-value line intersects the surface, and staged decompression dives are the ones where you hit the maximum M-value before you get there.

Yes, that has been understood from the beginning of decompression theory. Realizing that "no decompression dive" is really a misnomer that has confused people since it was invented, PADI now calls such dives "No Stop Dives," meaning that the decompressing you do while ascending at a safe rate is sufficient to take you safely to the surface. They do recommend a safety stop for most such dives as an added measure of safety.
​

A pure Haldane/Buhlmann dissolved gas approach will drive you shallow very quickly, and have you sit shallow to offgas. "Shallow", for a no-deco dive, is the surface.

Bubble models introduce deeper stops and slower ascents. I believe NAUI is now suggesting that even "no deco" dives should have a brief stop at half maximum depth.

Yes, the bubble models do introduce deeper stops and slower ascents. Recent research done in the last decade is making it look like that is not such a good idea. Refer to any of the recent threads in the technical diving forum related to deep stop theory. NAUI has backed off of its original thinking on deep stops for recreational dives.
​

Because we have built decompression into our model, we are able to do some depth averaging to determine the total time we can spend at depth. The tables built and taught by other agencies are made with other assumptions, which is why you are taught to take the maximum depth of the dive and run your tables from there. But it has never made a great deal of sense to me (nor is it the way any of my computers has run) to consider the entire dive done to 130 feet, if we went down there for two minutes, and spent the majority of the rest of the dive above 60.

It doesn't make sense to me, either, but then, neither does this plan. Back in the earliest days of decompression theory, "uniform decompression" (a steady, slow ascent rate) was the accepted norm. Haldane showed that "staged decompression" (which for recreational diving is what Lynne talks about when she says it drives you shallow quicker) was better, and I don't think research has changed that belief. The Min deco approach is much more like the uniform decompression theory that was disproved 100 years ago, and with no empirical evidence that it is better.​

 

[scubadada]

holy sh!t we agreed on something! write this down in the record books!

I wasn't aware that we generally disagreed

 

[tbone1004]

oh, one other thing that comes up with the discussion of half depth. Half depth is a completely idiotic representation of a theoretically good idea for decompression. They do that because in the US, it is very difficult for us to comprehend the metric system in our head so instead of what is a good idea of "half pressure" they take that to something "easy" and use it as half depth.

300ft is 10ata. Half depth is 150ft or 5.5ata. Half pressure however is 130ft. Much close to what your ascent profile is likely to have for your first stop.

Following half depth, your stops would be 150, 75, 40, 20, 10, surface
Following half pressure, they would be 130, 50, 25 *usually done at 30ft, then 20ft to get on O2*, 12, surface

You can see that with half pressure, which if you think about it makes much more sense than half depth from a physics perspective. You double the bubble size, then let them stabilize, repeat as necessary. Adjust those stops a little bit if you want/need to for the standard deco gases if you want to use them, or adjust your deco gases to accommodate those depths, but no matter how you spin it, half depth stops make absolutely no sense



the argument about the old nitrox divers feeling better and those that take a slower ascent profile stopping at half depths or whatever has nothing to do with the deco science on why they did that. Old nitrox divers are usually diving air tables with nitrox and doing so because of the lower nitrogen loading. They are subject to less decompression stress because of the lower tissue loading. They would have the same feeling if you gave them a computer and sent them for a dive profile on nitrox to the same GF Hi *nitrogen loading level when surfacing*. The difference here is that when they dive air profiles on nitrox, they are coming out with a much lower level of N2 in the body and because it is subject to less decompression stress, they feel better. Same with the people who adopt the min deco ascents or whatever. They are stopping for longer amounts of time which helps to offgas some of the tissues and they are subject to less decompression stress. Instead of going from 100ft and going straight to a 15ft safety stop, they are making a one minute stop at 50ft, one minute stop at 25ft, then stopping for however long at 15ft, the bubbles are getting less big. I would argue that if you took them up from 100ft to 33ft and had them sit for a minute or two, then up to 15ft they'd feel the same, but it's because they are decompressing longer and thus coming out of the water with a lower level of tissue saturation than a diver who came straight to the surface, or just went straight to a safety stop up from the bottom, usually with an ascent rate that is too fast

 

[boulderjohn]

This thread and others like it bring to mind the current anti-science attitude in America. So what if all those decompression scientists who did all that research that led to the dive theories those computers and dive tables are based on. I can tell just by looking around that they are all wrong and must have done terrible research!

​

 

[Kevrumbo]

You seem to have defined DCS in a manner in a way that it supports your position. Rather circular logic, isn't it? I'm unaware of any empirical evidence that would support your position that following a DC algorithm (whatever it might be) increases the likelihood of a DCS hit over ratio deco?

If you like I could dig out the Jaworski anti-computer rant to see one of the set of assumptions behind ratio deco. . .

People are, by and large, "safe" by the only standard that REALLY matters, too, right? They don't get bent. Even the ones doing multi-day repetitive diving. Right?

I've read some posts that RD is supposed to give ascents like using GF 20/85 or something like that, right? So, what is to be gained versus simply using a computer with GF 20/85? And, if you like, when the computer says no deco is required, still doing the very slow ascent (with "stops" - 10fpm, 30 seconds move, 30 seconds stop) as Lynne described?

From what I can tell, there is NOBODY that is trying to make a case that on-gassing or off-gassing is linear. So, doing anything based on an average depth will always boil down to a hack that is like a broken clock, right twice a day. It may get you out unbent every time - in which case it's more conservative than necessary a LOT of the time. Just like using PADI tables. But that's sort of moot, because it doesn't get you out unbent every time - and I know you don't need me to post links to threads where RD divers got bent. Heck, boulderjohn already mentioned on case of it in this thread already. Saying, "well that's not RD's fault. They didn't follow it right" doesn't matter (to me). They got bent because their "computer" (between their ears) didn't work right. And that kind of computer failure is a LOT more common than an electronic computer failure. And near-infinitely more common than having two electronic computers fail on the same dive.

If you do saw-tooth bottom profiles progressively deeper per @boulderjohn 's anecdote on a staged decompression dive, the chances of DCI will increase regardless whether you use RD method or a dive computer algorithm. In other words @stuartv , faithfully following your two computers can get you bent as well if you don't understand the inert loading/unloading & supersaturation effects on both slow & fast tissue compartments of doing such a stressful profile. The lesson learned & solution is to do the deep stops in this instance, and extend out the shallow O2 deco profile (per the implications of the NEDU DeepStops Study).

Anyway the thread is about using the Tables to NoStop/NDL times on Nitrox32.

. . .I know such a person. Every time she is on a boat, she takes headache medications along with sea sickness meds because she "always gets a headache after a dive and feels like sleeping" (Type 1 hit). When the dive is over and the boat is returning, it would be a two hour trip back to Morehead city NC. You will always find her sleeping on the dining table with headache meds and it would be pretty hard to wake her up. Since a whole bunch of people use those tables to "crash after a dive" such behavior has become an accepted part of NC diving. Try convincing her or any of these others "sleepers most of whom would be with headache meds" that they are experiencing a type 1 decompression hit and they will pull out her Suunto and tell you "I use my computer and I always dive safe!"

Decompression is not an exact science and when you build precision devices to measure something you have not really defined, then you start an era of "computerized stupidity." Whether UTD and its Minimum Decompression is the best way to solve this, is something I am not sure yet. It is an option that was built to address this flaw so lets give it a shot and see what happens?

The post-dive "always gets a headache" of your friend is not a good sign. Rule-Out exertion Hypercapnia, Skip Breathing for starters, and/or possibility of a Right to Left Shunt (i.g. PFO). A safe solution for now is diving conservatively with Eanx32 on Air Tables like the HUGI Table or Air dive computer setting.