Trivia Question: Where Would You Be At 1/2 Ata?

[Padipro]

tankajava once bubbled...
I'd be at Peterson Field, Colorado Springs in the altitude chamber requalifying for my flight physical.

Rapid decompression from 15,000 feet and up is pretty cool. Anoxia is a cheap high providing the chamber tenders are on the ball.......

Tank,

The chamber is pretty cool isn't it? I remember my first flight in one. I took my mask off at 30,000 and tried the little puzzle game. It only took me about 30 seconds to put all the pieces in but as the Instructor was trying to remove them so I could do it again I damn near blacked out. What a rush. The wildest thing was how badly your night vision is effected. The rapid deco scared the S**T out me though. I wasn't expecting the loud BANG as the valves slamed open.

Scott

 

[Charlie99]

cnidae once bubbled...
Now lets look at it this way. I believe the 2:1 ratio was determined somewhere near sea level. What it's missing is the amount of molecules absorbed into the tissues is the real reason for getting bent it’s not just the pressure decrease. Just as an example, if I was on the moon with an ATA of 0.1 and I submerged myself to 0.3 of an ATA and saturated, your telling me I would have a good chance of being bent? Think about how few molecules your actually absorbing with the pressure change because you started out with far fewer than if on earth.

What I'm curious abut is how much of this is what you learned in your recent class.

Since a common GUE refrain seems to be to label Buehlmann as a "bend and treat them" model and to claim inside knowledge of advanced models by people such as Bruce Wienke, let me throw in a few direct quotes of BRW: "Generally, bubble growth and excitation are compounded at altitude because of reduced pressure". and "Bubbles grow faster as they get bigger, and as pressure drops. With decreased pressure, bubbles will also expand by Boyle's law. Bigger bubbles are not as constricted by Laplacian film tension, while reduced pressure supports a faster rate of tissue gas diffusion into the bubble itself."

Bruce Wienke says that "the air saturation curve passes through the origin as ambient pressure drops, behavior predicted within phase models" He then goes on to give the general equation that he has deduced: Q=[2.37-exp(-11.1/P)]P. As P (the surfacing pressure) goes to zero, limit on Q (the initial saturation air pressure) is 2.37 * P. For very high levels of P, Q approaches 1.37P + 11.1fsw. He chose his limits using the permissible bubble (Doppler) excess as the phase limit point. This results in a much more conservative 1.66::1 ratio at sea level, as compared to Haldane's 2 to 1. Ignoring practicalities such as hypoxia and H2O vapor pressure, the answer is YES, you have good chance of getting bent from a 0.3 to 0.1ata pressure change (3 is greater than 2.37).

As I stated in an earlier post, a lot of decompression is controlled by RATIOs of pressure, not just absolute pressure or "the amount of molecules" as you put it.

If you don't wish to wade through the math, let me simplify it: according to a wide variety of people that have done both practical and theoretical studies, Altitude DOES matter .

I am alway open to additional information and theories. I'm neither a hyperbaric nor hypobaric expert and appreciate any comment/corrections on the above.


Cnidae, I would greatly appreciate it if you could clarify a few points:

1. Were you actually explicitly told by GUE instructors to ignore altitude in your planning? Or to phrase the question more directly, were the dive planning calculations posted by Kevin Metcalfe the ones taught in your rec triox class?

2. Did the GUE instructors give any explanation or justification for ignoring altitude in your dive planning? If so, it would be very helpful if you could at least give a general description of that explanation.

Thanks in advance,

Charlie Allen

 

[cnidae]

Charlie99 once bubbled...
What I'm curious abut is how much of this is what you learned in your recent class.
Charlie Allen

There was an explanation but I think your looking for more than I was told. We did'nt get into it in depth. I would contact the insturctor if I was you to get the reasoning from the horses mouth. Wish I could help more.

 

[tankajava]

Padipro once bubbled...


Tank,

The chamber is pretty cool isn't it?

Scott

Scott,
The BANG caught me and my drawers unawares too. I was literally in a fog when the water condensed out that rapidly. Couldn't tell Aces from Kings in a deck of cards after 30. The Vista Vertigon taught me a few things about spatial orientation too but they didn't have any training to prepare me for the rapid G loading during a Navy T-2 Buckeye test flight. Roll and dive rate was so fast that everything tunneled to a pinpoint in front of me. Closest to G-LOC I ever came and that included DACT rides in F-15Bs in the 6 - 7g range.

t-o-j

 

[Charlie99]

cnidae once bubbled...
There was an explanation but I think your looking for more than I was told. We did'nt get into it in depth. I would contact the insturctor if I was you to get the reasoning from the horses mouth. Wish I could help more.

I did try to get info directly from MHK over on rec.scuba. Unfortunately, I was away on a dive trip when the trip report was first posted, and by the time I inquired about the altitude stuff, passions were already heated and he declined to make any substantive comment. I guess I have to stop letting diving interfere with the cyberdives. Your comments, Cnidae, have indirectly shed quite a bit of light on the quality of the decompression theory lessons of the Rec Triox course.

Some rec.scubians questioned whether a 120' 20 minute dive on 30/30 is NDL (it isn't on any deco program I am aware of, including GUE's). MHK answered that a 100' 20 minute 30/30 dive has just 1 minute stop at 30' and 2 minutes at 20', so it isn't all that different from a "NDL" dive that calls for a 3 minute safety/deco stop. When it was not so politely pointed out that it was 120', not 100' MHK responded with some insults about GUE concepts being over the head of those that can't tell the difference between average and max depth (an interesting spin on things since the discussion was about Kevin's method of calculating NDL for 120' 20 minute 30/30 dive. My guess is that MHK did the EAD calc from 120' to 100', then plugged 100' into decoplanner with 30/30 rather than air).

It was at this point I asked about altitude, since altitude further pushes the dive into deco territory and it is very unusual to ignore a 6,000'+ altitude in dive planning. MHK was less than responsive.

As his continuing conversation with others, MHK posted that "solubility was covered in great depth", and referenced Graham's Law. I did note that one of the first responses you made was to post a reference to solubilities. That is basic dissolved gas physics and doesn't explain, to me at least, how GUE has come up with the two unusual conclusions that 1) altitude doesn't matter, and 2) a 120', 20 minute dive on 30/30 is an NDL dive.

I'll probably let passions die down, and then ask the question again in a couple of weeks, but all indications so far is that I won't get an answer, because they don't really have any valid reason for those two statements.:

 

[Doppler]

Why the **** are we playing with Grahams Law of Diffusion in a recreational diver program? I bet good money that less than half of course candidates can prove the math. Which may or may not be germain -- and we've come a long way from the thread's original purpose. But why bring it up if you're not going to work through the math to illustrate the "ACTUAL" outcome.

Wouldn't it be far more productive simply to say: "lighter gases -- such as helium -- on gas and off gas more rapidly than heavier gases?" Rather than getting into diffusion being inversely proportional to density... most folks don't know or care about moles and avogadro's number, and few can quote the atomic weight of oxygen, nitrogen and helium... And you can't quote Graham's without strong association with the rest.... sounds suspicious to me.

One might also use Graham's to illustrate why bubble formation iin presence of dissolved helium is particularly prone to "runaway" growth. And then to point out why playing with helium at high altitudes can have disasterous results...

Chemistry man... wow, it's a double-edged sword... give me physics every time...

Just a thought

 

[Doppler]

Charlie99 once bubbled...
SNIPPED

a 120', 20 minute dive on 30/30 is an NDL dive.

I'd be interested to find out which algorithm someone is citing to prove this point.

Unless someone is ignoring two things... Various gas laws including Graham's Law, and modern decompression theory.

Last I heard, the definition of a NDL dive was one from which you can ascend directly to the surface. The stops called for in this example are minimal; however, ignoring them (the first is at 40 feet according to heavily modified Buhlmann and 30 using VPM-B) will get you bent at any altitude, sea level, 6,000 feet or 6,000 meters... whether the hit is chamber bent or aspirin bent is a point for debate. But bent you'll be. Calling a 30 foot and 20 foot staged decompression stop a safety stop is simply wrapping a wolf in sheep's clothing... this is going to bite someone.

 

[jrmy_1]

I just ran 120' for 20min on 30/30 with no conservatism on V-planner B and it gave a mandatory deco with 1min at 30' and 5min at 20'. This was for sea level. At 6000' above it gives 2min at 30' and 13 min at 20'. I don't understand how you can get away with 120' for 20 on 30/30.

 

[pufferfish]

If anyone is interested Lake Titicaca at 12,000 ft which straddles the Bolivian/Peruvian border (Peruvians claim the 'Titi' part is theirs and say 'caca' belongs to the Bolivians!) is diveable if you bring your own compressor and gear.

Lake Titicaca Dive

Interesting part about getting the air/fuel mixture correct on the compressor and feeling better at depth on higher ppO2.

Just some interesting trivia about La Paz, Bolivia's International Airport in case you decide to go.

1. The airport is at 4000m or about 13,000 feet. As most people fly in from Miami there is a Praxair office open for all flight arrivals.

2. The runway is twice the normal length (?20,000 ft) and it is the only time I have been on a flight where I equalized my ears on take off not landing. Any ideas?

3. No small private airplanes are see stored at the airport as this is above their operational ceiling.

Anyone interested in a dive/ski/climb expedition??

Ok back to debunking GUE's claim that altitude doesn't matter in dive calculations

 

[cnidae]

jrmy_1 once bubbled...
I just ran 120' for 20min on 30/30 with no conservatism on V-planner B and it gave a mandatory deco with 1min at 30' and 5min at 20'. This was for sea level. At 6000' above it gives 2min at 30' and 13 min at 20'. I don't understand how you can get away with 120' for 20 on 30/30.

Lets set one thing straight. This class was not a NDL class; all dives are considered decompression dives by GUE. This class was taught as a minimum deco class. Run your profile again using 32 opposed to 30/30 and see what you come up with. It should be somewhere around 3 minutes of stops. What’s happening with what you ran is the software is penalizing you for the helium when it shouldn’t be. I'm not a deco expert but what I think is happening is the software algorithm considers the helium to dissove imediately when it does'nt. Now take the software and make it so that your stops are at an 80 pause, 50,40,30,20,10 this is more realistic to what we did. As far as the altitude stuff nothing I stated came straight from the instructors mouth so I would'nt quote it when asking them questions.