Hey Dave!

Dave Sutton

Nice work on the rig. Azimuths are *the* great CCR conversion platform. Nothing else makes as nice a rig. Now I wish I still had one.... ;-). Have to keep an eye on EBay.


Bill Sewell.... maker of the "Arctic Lung" before he moved from Alaska to the great West. He's an old friend. One day long ago I sent him an aluminum 1 litre pony bottle that has a crack in the neck for "test to destruction". He filled it with oil vapor and then tried to make it explode by filling it with pure 02 at various (high) rates. He tried and tried and tried and tried and he could not make it burn. Then he was stuck with it.... I think he finaly shot it with a 7.62x51 tracer from a rifle to end its misery. He made some neat counterlungs for a while, sent me some samples. Good guy. Not sure if the suit is a joke or not, from anyone else I would say "yes" but he has a track record as a self-kind experimenter. But again, with a FFM and no gas-path flow control (IE Oral Nasal or DSV) unless he's got an open array scrubber bed in the thing there's no way to scrub the gas. Have to ask him.


Nobody has comments on constant bouyancy = constant PP02? Thought that would stimulate discussion.... maybe it's old hat.


Dave

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schford

Couple of threads on it some where, as a great tool to use to exit a structure when you can't read handsets for what ever reason and are at a level depth...

*grins* tis a useful tool though.

Stuart

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Padowan

I'll pick up on this....

I've had a play with th 'constant loop vol @ fixed depth = constant PPO2' and have used it sucessfully (as a trial excercise) to maintain a PPO2 within 0.1 of my desired value for over 30 minutes bimbling about in a quarry at constant depth - I certainly now include this a tool in my toolbox for dealing with any electronics failure during the bottom portion of a dive, to get me back to the shotline for example.

I've been thinking about possible ways to expand it's use, and as you rightly say, the PPO2 that you can maintain totally blind (at constant depth) is dependant on the dil that you are able to flush with. I still carry OC bailout, and so with 2 tins plus the inboard dil and the O2, I theoretically now have 4 known mixes that I can confidently maintain blind at constant depths. My caveat to this, and I've not tried it yet, is that once you embark on your ascent and get to a stop depth, you can flush with a known gas and get to a known PPO2, minimum loop volume. Now, your body is metabolizing O2, reducing loop volume, but at the some time you're offgassing inerts, so you can't accurately assume that loop volume drop requires O2 injection at a 1:1 ratio, as some of the required "space" that the correct O2 slug would replace has already been replaced with inerts. As I've not tried this, I can't say how big an effect this is, but I suspect that it's not insignificant, especially if you've used a lot of Helium in your mix.

So, for me, without lots of experimentation at trying to work out a "good-enough" blind ascent protocol, my strategy to maximise CCR usage with no electronics would be to go blind CCR on the bottom, OC for the ascent to 6m, then back on the loop O2 CCR.

One experiment I should try, is to see how much of the ascent (particularly the deep portion as this is where the OC gas requirements would be highest) I can still do within an acceptable PPO2 tolerance. For example - dive to 90m - 10bar ambient, perfect (for this excercise) dil lets say 13% O2 = 1.3bar PPO2 dil flush at depth, maintain blind to the shotline manually injecting O2. Now, if I ascend to 40m, the ambient pressure halves to 5 bar, so I would expect the loop PPO2 to be at best half the original, but in reality less as I will have metabolised some O2 - so a maximum of 0.65, but probably quite a bit less - the question is whether it's significantly less to the point that the loop is now not viable. If I try some REALLY rough calculations I can try to approximate what the loop PPO2 might be:

Assume min loop vol = 10L total (5L tidal, 5L fixed)
10L x 10bar ambient = 100L total gas in loop
@1.3bar PPO2 at the bottom = 13% O2 = 13L "surface" O2 present in the loop.
So.. to make the calcs worst case, lets do the ascent, then assume that the metabilised O2 comes out of the ending state:

Ascent to 40m (lets say that this takes 5 minutes as we're in a bit of a hurry!)
New ambient pressure = 5bar
Loop PPO2 drops to 0.65bar (13% O2 @ 5 bar)
Back to minmum loop = 10L total @ 0.65bar = 6.5L O2 in the loop.

Now lets remove the metabolised portion:
5 mins @ 1L/min = 5L over the course of the ascent.
6.5L in loop - 5L = 1.5L remaining in a 10L loop @5bar (50L) = 3% O2
3% O2 @ 40M = 0.15bar PPO2

So from this I reckon that an ascent from 90-40m, maintaining minimum loop volume and NOT injecting O2 during the ascent would result in a loop PPO2 of somewhere between 0.15 and 0.65bar PPO2 (excluding offgassed inerts).

Seeing as the calculation was really worst case, and ALL the O2 metabolised came from the smallest, leanest loop of gas then I reckon that the loop would still be viable. So this situation would allow me to not require OC bailout for the portion of the dive from 90-40m which could potentially be a lot of gas. And the other caveat to this is that at any point, I could dil flush again, and bring the PPO2 back up to a known viable level based on my depth and dil/bailout gas

So at the end of the day, it would be nice to have a "system" that allows you to ascend to some ambient-pressure-ratio depth (like half the pressure in the previous example) and be confident that the PPO2 decline from both pressure loss and metabolism was such that you can maintain a viable loop totally blindly. The problem of managing deco then comes up, but I've not thought about that at the moment....

Any comments?

*** DISCLAIMER ***
These suggestions and calculations are REALLY rough and off the top of my head while I sit and think in front of my computer. No guarantee that their not complete rubbish, in fact they might kill or injure you. Don't use them.

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Dave Sutton

You're right, and I was wondering if anyone would pick up on this. Inert gas being passed back into the loop mix during deco is a similar issue as when initiating a dive on a pure 02 rig.... isobaric decompression on pure 02 rigs ends up diluting the loop gas with offgassed nitrogen..... which is why we do a full flush with 02 after the first 30 minutes when diving 02 rigs "blind" (which is the usual case). Isobaric decompression is also why pilots flying extreme high altitude aircraft (research aircraft/ U-2, SR-71, etc) prebreathe pure 02 for a half hour before doing high altitude flights (the decompression from the combination of altitude and pure 02 breathing can cause symptiomatic DCS, which is why the USAF has more chambers than the Navy...)

Back to what you wrote, use of this as a mode of operation is one of the reasons I have opersonally chosen diluent mixes that are higher 02 fraction than many other users. In your example, my belief is that the fraction 02 diluent is way too lean. I want the blind mix to be good "as-is" as shallow as possible, preferably viable at the surface. I'll accept bottoming out "hot" in return for being OK shallow. You can run hot for a long LONG time. You cannot run weak for a minute......

Think that in a real world bailout I'd flush anyhow every 30 minutes with fresh diluent. Too many monkeys chattering on my back to not want to do that as a sanity check. Naturally, as soon as I was at 40 feet I'd be on pure 02 anyhow so the time spent attempting to maintain a constant loop PP02 with any diluent in the loop would be minimal. Don't scream about using pure 02 at 40 feet..... I don't care what the current civil training groups think. 40 foot pure 02 in-water deco was Navy Standard when I learned how to mixed-gas dive and if it was good practice then, it's good now. Then again, we also did 60 foot for 30 minute "oxygen tolerance tests" in the chamber on a periodic basis just to see if any indvidual was not tolerant to hyperbaric 02. Nobody EVER showed the slightest sign of tox symptoms and that was after several hundred tests done while I was around. How well I remember chanting "VENTID..... VENTID...." while in the water at 40 feet on the stage. "Vison, Ears, Nausea, Vision, Irritibility, Dizziness...." the old Navy Saw for detecting 02 tox.


A more interesting discussion is that of the VSC bailout mode. Has it been discussed recently?

If so, I don't want to:





Dave Sutton

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"Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com

Philippe GERIN

Yup, I'm another one who started CCR diving converting my Azimuth SCR with Kiss parts thanks to Dave Sutton in the concept and with some help via e-mail.
Again, a warm welcome on this board Dave.
Best
Philippe

jaap

Hi Dave

So did you get your cryo diving apparatus filled and dived yet?

About the out gassing of nitrogen while diving a O2-Rebreather I recall that a normal man holds about 2l of dissolved nitrogen at standard conditions. I have a article that mentions it if anyone is interested. Its quite easy to make a rough but fairly accurate estimate of the amount of dissolved gas at saturation for different pressures if one assumes that Henrys law is valid for humans.

So I don't think that the nitrogen outgassing is an issue for O2-Rebreather dives as long as the loop is reasonably well flushed to start with. The slow but steady out gassing of CO from humans is a more interesting sidetrack and possibly a reason to do flushes on long dives though.

About the dry suit counter lung Rebreather:

http://web.archive.org/web/200112031...HastrmanDS.htm

http://web.archive.org/web/200502220...HastrmanDS.htm

Its a pittty those pages are not supported any more. I only vaguely recall the pictures. Anyone have them stored?

Dave Sutton

Ahh.... the Cryrogenic SCUBA: Jens and I were talking about that very thing last week, next time I have space to carry it to Rhode Island I will give it to him for study. I would like to get it diving, and do not think it will be too hard, just have not had a lot of time to play with it. I tried for years to track down the old Diving Officer from FIT (my alma mater) James Woodbury, who designed the liquid-air SCUBA that was sold by Jordan Klein (Mako) in the 1960's so I could discuss it with him, but he's apparently run off to India and has not been seen since. The idea is fascinating, just need to source premixed cryogenic gasses other than 02. Anyone know about simple liquid mixing of two cryogenic liquids (IE helium or nitrogen) and 02 to make a liquid mixed gas? With different temperatures of liquidity, one must think that the mix would be changing in storage pre-dive, but I would like to know to what magnitude.

For those not "in the loop", I have here in the little diveshop of horrors a Russian cryogenic diving apparatus consisting of two dewer flasks of about 4 litres each with the piping and regulators to allow them to be used as a diving apparatus. This is the Russian "Cryolang" and I think I hold the only one in private hands, obtained thru a deal from Ukraine... not sure who got it from who there, traded to me for a wad of $100's....brought across the border in the secret boot of an old Tatra.... (you actually believe this stuff?)

Truly, all I am missing is the breathing regulator diaphragm andf cover, easy enough to make. I will do it.

Photos are Jan Willem's site here:

http://www.therebreathersite.nl/cryo_pjotrr.htm



Drysuit rebreathers.... what will they think of next... ;-)


Dave Sutton

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fubari

Now that is a mind blowing idea.
Still, fun to ponder.
I was wondering how much helium would boil off
if you poured in 1 litre of liquid air.
Then I noticed air's melting point is rather higher
than helium's boiling point.

"Dil Sorbet" comes to mind.

-----------
Helium:
boiling point: 4.22k (-268.9c, -452f)
melting point: none, at normal pressures
0.95k ( -272.2c, -458f) at 2.5 MPa (or 24.7 ata's, or 362psi)

Air:
boiling point: 78.8k (-194.35c, -317f)
melting point: 56.95k (-216.2c, -357f)

Oxygen:
boling point: 90.2k
melting point: 54.36k

Nitrogen:
boling point: 77.36k
melting point: 63.15k
----------- #'s from http://en.wikipedia.org/wiki/Cryogenic ---

At best, given enough liquid helium, the liquid air
(or O2, or N) would freeze, yes?. Gives a whole
new ring to the phrase "gas blender".

For this cryo-thing, you're talking open-circuit.
Your "back-mount dewars" would be liquid filled.
That is an interesting tradeoff: "low pressure liquids"
vs. "hi pressure gases".

With separate He & O dewars, mixing could be done
downstream of the "regulators" in gaseous form.

But... how does a "demand regulator" for this work?
Sort of an "anti-opv"? e.g. isolate the liquid from the
heat-exchange coils once a target gas pressure is
reached?

At depth, if you're drawing more gas, hence vaporizing
liquid quicker, how would you stop it from freezing
into your own personal back-mounted iceberg?

Still, it boggles my mind. It is hard to imagine the
infrastructure you'd need to handle liquid "gas blending."
I'm guessing it makes the haskell I'm saving for look cheap.
What is the shelf life of a dewar of liquid helium?
Loss of 1.25% to 3% boil off per day?
(from http://www.intlcryo.com/popups/transport.htm)

Anyway, I've always enjoyed your writings.
"thought provoking" is the phrase that comes to mind. :-)

John G.

Drmike

so would I.

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Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

Dave Sutton

OK, two topics:

Cryogenic SCUBA: These were well tested and sold commercially by Mako (Jordan Klein, who was a well known film maker of the 60's formed "Mako" to sell stuff they invented for filming). Obviously, the system allows rebreather-like durations with OC simplicity. The liquid is boiled off to gas by passing it thru heating coils that are simply heated by the water ("Hot" is all relative...). The resultant gas is simply dispensed to the diver thru a standard open circuit second stage. Mako used a single hose regulator and the Russians used a double hose design. Bottom line: A Dewer, a length of tubing coiled and exposed to the water, and a secnd stage hooked in at the end are the essentials. Naturally there are other complications: accumulator to hold the gas ready to be breathed, traps to prevent a slug of liquid from finding its way to the divers mouth (that would be bad...), etc. But this is really common technologu, we use LOX in the T-38 (aircraft) 02 system, and it's simply boiled off, plumbed to a regulator, and breathed in by the pilot. LOX converters are filled and stay filled for 2-3 days on the flight line. Not rocket science... (OK, it *is* rocket science but who's counting...) ;-). The photos on Jan Willem's site shows the demand regulator clearly.

Not really a rebreather subject, as with the durations of gas available in a Dewer, scrubbers would need to be HUGE to parallel scrubber volume wth gas supply volume. Best Rebreather application would be to ensure adequate bailout gas with a cylinder held internally in a rebreather... small = good.


Chest mounted minimal rebreather.... OK, I'll do a photo shoot next week and post it here. EXPLORER is running 4 days to the U-853, still have spots for Sat/Sun if anyone wants to come.


Dave Sutton

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"Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com