Debate is what forums are for. We might have different opinions and that is fine with me. If you are out in the field for long periods your life would be simpler filling one dil bottle :sarcy:
I wouldn't do 100m with less than 70%
How Many Off Board DIL's to allow for?
- Thread starter divingtactics
- Start date
Debate is what forums are for. We might have different opinions and that is fine with me. If you are out in the field for long periods your life would be simpler filling one dil bottle :sarcy:
I wouldn't do 100m with less than 70%
1 - not monitoring is not the same as 3 - solenoid failing.
80m DIL is still hypoxic assuming 1.2
Janos
"Two sheds"
I had it as ADV misfiring leads to ppO2 crash (nothing to do with solenoid) (one problem) and diver fails to notice (second problem).
I use 15/55 to 15/60 at 80m. ppO2 is a little high at 1.35; but I prefer the risks of it being hard to flush down to the sneaky risk of hypoxia.
Janos
Dave Sutton
Banned
"Could" do it the way the Cis Lunar Mk-5p was designed to be used (and note that the onboard DCAP decompression software supports this):
Diluent #1: Air
Diluent #2: Heliox (no nitrogen)
Procedure:
Descend on air until you reach your desired END, say... 100 feet, 30 meters, etc. this sets your nitrogen content.
Switch to Heliox diluent and continue descent. Now all you are adding is helium into the inert gas fraction. Result: constant END for the balance of the dive.
This procedure is described in detail in the Cis Mk-5p manual (which is the best rebreather manual I've ever read, btw), and there's a software setting in the DCAP to handle the resulting deco.
Or you could do what we had as diluent in the PP's (basically a helmet and umbilical connected CCR-1000): pure helium.....bearing in mind the design depth range of 300+ meters. Then again, the ADV of a CCR-1000 is unlike any other.
Flipping one valve at 30 meters to swap diluent is not that much work.
If I can ever *ever* get another Cis Lunar switch block to put on my Meg, I'd have the perfect rebreather. After I stuck the Cis waterproof scrubber into it... ;-)
Dave
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Diluent #1: Air
Diluent #2: Heliox (no nitrogen)
Procedure:
Descend on air until you reach your desired END, say... 100 feet, 30 meters, etc. this sets your nitrogen content.
Switch to Heliox diluent and continue descent. Now all you are adding is helium into the inert gas fraction. Result: constant END for the balance of the dive.
This procedure is described in detail in the Cis Mk-5p manual (which is the best rebreather manual I've ever read, btw), and there's a software setting in the DCAP to handle the resulting deco.
Or you could do what we had as diluent in the PP's (basically a helmet and umbilical connected CCR-1000): pure helium.....bearing in mind the design depth range of 300+ meters. Then again, the ADV of a CCR-1000 is unlike any other.
Flipping one valve at 30 meters to swap diluent is not that much work.
If I can ever *ever* get another Cis Lunar switch block to put on my Meg, I'd have the perfect rebreather. After I stuck the Cis waterproof scrubber into it... ;-)
Dave
.
matt
Well-Known Member
I'm late to the party, sorry for that.
I've made several dives to 130m and I didn't do anything complicated - I find complicated doesn't work.
I'm not concerned at all about hypoxic mixes - I'd take a 6/72 as my dil for that dive (although due to blending issues I actually had a 5/80, don't ask).
I have a flow-stop and I turn if off for ascent. For descent I sit and do all my checks on the bench including sounding the low PO2 alarm and watching the displays stabilize.
Looking only at the CCR I would not do any sort of flush. I have found it doesn't work for me. I put the SP to 1.5 on ascent (from about 90m as I am get-go) and I'll run the CNS instead. It's not PC.
I keep the overall time to 5 hours max - that's all I could be bothered with. You'll get 25-30 mins depending on your tuning.
In the early days on these dives I have run out of O2 on ascent. The root cause - MLV. In the shallows you off-gas a lot. This dilutes the loop and the solenoid opens wide.
Since running out I have focused on MLV more (at 6m) and have been getting out with >50 bar. I carry a spare 3L O2 250 bar anyhow.
The only other diluent I carry is Air and I use the for suit-feed, but it is available for diluent use via a whip if needed. It never has been outside of an air flush which made me very fatigued and which I no longer do and would not recommend.
Cheers
Matt.
Andy Del
still causing trouble!
I quite like the idea of this, reasonably simple and elegant. :wavey:
But this:
is quite appealing. I'll be sitting through a lot of down time at work this afternoon and will mull it over. Thanks for the info, Dave!
cheers
Andy
p.s. mulling is NOT what you 60's children think, it's thinking over this part of the world - I am doing what my avatar shows (same gig 2 years ago)
A
anarchista
New Member
:devilban:This variant TMX mixing is sensitive to the loss of gas from circulation, then we do not have any control over ppN2.
Also, we can not easily play the right mixture.:devilban:
greet rc
Yup, therefor it does not make sense. It would make sense if it was designed to perform a switch from pure N2 inerts to pure heliox, by performing a flush when switching. Keep in mind that this type of switching was common, and IBCD not really a known part of diving. A mask clearing or slight bubling from the mask seal will change the mix. Over several hours which the cis was made for you would end up far away from the intended mix. Going up and down would allso destroy your mix.
I cannot belive this to be the intended modus operandi! Does it really read as that Dave? I.e. "Constant" ppN2?
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anarchista
New Member
With only one compression, without loss of gas from the circuit, ppN2 remain constant. For the same equipment, just to start the ascent.
Unfortunately, the man in the gas dissolves, fat tissue 5 times more nitrogen than the aquatic tissue. Even if there is no loss of nitrogen due to leakage, it still will drop ppN2.
The same statement without understanding what is happening in the circuit, produces half-truths.
greet rc
Dave Sutton
Banned
Yes, it's absolutely and most definitively described this way in the manual. I'd need to boot up the rig and play with the brick for an hour to find the mode selection to do this. You can toggle between this mode and standard Trimix deco during the dive (IE: you flush the rig) but it is absolutely designed to be used as I describe it.
Dave
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Well seeing this is easy to calculate and implement in the software, I suppose they just put it in because you can, when the switchblock is there. Hell why not?
Not thats its a good idea, unless you are doing a deep bounce dive. Then i suppose it would make a nice idea, as long as you dont have any leaks from mask and dsv.
anarchista
New Member
Reasons for doing so are understandable, heliox does not like rapid compression (HPNS). Unfortunately ppN2 does not remain constant, for a number of reasons.
greet rc
I doubt that very much there would not be that much gas dissolved in the body to make that much difference and noticable in anything other than perfect controlled conditions, particularly when you factor in differences in rate of uptake. All it takes is one mask clear (or other leak) and all bets are off on what the ppN2 is.
I used to dive my Mk15 liek this about 12 years ago. Then we worked out it was too much hassle making the switch and just dived with Heliox anyway
anarchista
New Member
On the effects of leakage wrote a little earlier than you. This argument is mine.
The saturation of the body also have written before, I can also calculate how much nitrogen is dissolved. Will help decompression model Jones and this table:
http://rebreathers.pl/forum/download.php?id=104
rc greet
anarchista
New Member
True, diving physiology and physics are not important. Important as it is written in the manual.
greet rc
I wonder why this literature is only in Polish as English is the language of science? Why is the work is not suitable for publication in international peer reviewed journals?
I translated some terms to understand what the table is saying
szybkosc wyplukiwania azotu przez tlen z roznych tkanek ludzkich = leaching speed of nitrogen by oxygen in various human tissues
zawartosc wody = water content
zawartosc tluszczu = fat content
zawartosc azotu = Nitrogen content
krew mosg = blood brain
miesnie skora = skin muscles
kosci komórkowe = bone cell
kosci szpikowe = bone marrow
tkanka tluszczowa = fatty tissue
Reading the table total Nitrogen is 850mL (I am guessing at surface pressures but hard to translate and can't see any evidence of pressure).
If we take Dave's example of switching off Air Dil to Heliox at 30m.
It tissue are fully saturated at 30m. Assume SP 1.3 so ppN2 is 2.7 Now we take off 0.79 that the body was saturated with from surface we have a max of ~1.7 (1.91 x 0.85L) of Nitrogen that can saturate into the body.
Now we can calculate how much Nitrogen in surface L (2.7/4 *10L (assuming loop volume of 10L) *4 is 27L. This means if we are fully saturated we can absorb 6% of the Nitrogen in the loop. So liek I was saying practically impossible to see - especially (given accuracy (note I didn't say precision) of O2 monitoring) and more importantly how long it would take to fully saturate the body and all the other factors such as differential on gassing of N2 and He.
Now to WFO's post ...
Taking the table (and in addition to all the posts on the subject before) - the PO2 drop you are seeing is not off gassing.
Why the max pressure even if the whole body is saturated is 1.58 (workman) x 1.6 (ata at 6m) is 2.56 = 2.2L that could off gas into the loop which is 13% of a 10L loop at 6m. Now who dives to saturation and arrives at the 6m with all tissues at Mvalue of 1.58?
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HUH ... WHERE'D THE POST GO???
No idea where you have pulled your numbers from - we need more explanation.
Either way I wrote ~1.7L you said 1784mL - same thing.
Importantly 5-8% (you) 6% (me) of loop volume are pratically the same thing AND - all this assumes full saturation of the whole body and very very few people doing that (I can think of a handful of deep cave diving teams), not to mention all the other variables, not least the accuracy of the O2 cells (which we measure the other gas by default).
So whilst interesting academically - meaningless real world.
No idea where you have pulled your numbers from - we need more explanation.
Either way I wrote ~1.7L you said 1784mL - same thing.
Importantly 5-8% (you) 6% (me) of loop volume are pratically the same thing AND - all this assumes full saturation of the whole body and very very few people doing that (I can think of a handful of deep cave diving teams), not to mention all the other variables, not least the accuracy of the O2 cells (which we measure the other gas by default).
So whilst interesting academically - meaningless real world.
anarchista
New Member
After calculating the mass of tissue water that comes on the surface there are dissolved in 447 ml of N2, in the fatty tissues 434 ml
At a pressure of 2.7 indeed dissolve at an additional 871 ml and of fat tissue 434x (2,7-0,75) = 846 ml
1717 ml of total nitrogen.
I'm impressed you realize this right.
I deleted, the errors were.
greet rc
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divingtactics
Serious Swagelok Addict
No worries Matt, better late than never.
I'm running twin 232 bar 7 litre steels on my rig and I do have a flow stop on my ADV if needed.
Post this whole thread, I've pretty much decided that I'm going to run with normoxic in my onboard DIL and will connect the deep gas with a QC6 and check valve on the surface but not turn on the tank valve till at a safe depth of around 20m. So the procedure is similar to what I've done with open circuit and I'd switch off the onboard DIL tank valve and then turn on the offboard Hypoxic tank valve. It means we are not unplugging and plugging at depth and keeps it simple. On ascent, the reverse would be done, turn off offboard DIL tank valve at 20m and turn on onboard DIL tank valve. This way, we never have a non breathable gas connected to the BOV or ADV, regardless of if the ADV flow stop is used or not.
We also have a cheater reg with a LP inflate nipple adapter on it that we keep in a spare pocket and can connect into the MAV O2 feed hose, that will allow us to access the onboard O2 if we had to bail out.
I'd be interested to know what your CNS clock ends up on at the end of the dive with a 90m start on PPO2@1.5? Not sure I'd be too keen to run it that high that early.
Thanks for your input, much appreciated.