Diluent selection and the great alpinist v siege debate

Simon Mitchell · 3rd January 2007, 01:15

Quote: (Originally Posted by jradomski)

Hi Dave,
There have been a few studies (more is needed) that different inert gases effect our resistance to oxygen issues.. Evidence suggests Helium increases our likelihood for a problem while N2 reduces it.. So if we make the breathing easier we increase our risk by the inert gas but lower co2 retention, if we have alot of n2 we reduce our risk by the po2 but increase our risk due to co2 retention..

..

Hello Joe,

Can you please point me in the direction of this evidence??

Thanks,

Simon M

***jradomski*** · 3rd January 2007, 04:50

Quote: (Originally Posted by Simon Mitchell)

Hello Joe,

Can you please point me in the direction of this evidence??

Thanks,

Simon M

I remember reading 2 studies.. I'll see if I can find the links.. one was posted at some japanese medical journal repository..

There was also a summary posted online somehwere that I read a few years backed that showed various po2 issues at lower po2s that occurred while on gases with high Helium, while in the pas there are no reforted issues with people with similiar exposures while using air based gases..

Here is one article That I had on my laptop... This isnt the one I was think about but it has a few addtitional links..

NEwreckdiver · 3rd January 2007, 19:49

Hi Dave and others -

I just wanted to say this has been a very interesting discussion that has given me a few things to think about. I realize now the discussion is caught up in the high PO2 issue, but that aside, I think Dave has some very valid points about diluent choice, especially in a bailout scenario where you may be going semi-closed. Personally I have never (yet) truly understood the reasoning for "10/50 all day long" on the CCR. I am admittedly a new rebreather diver and am still quite comfortable diving air diluent on <130 fsw dives, but every dive I do looks to the future when I will be using other gases and therefore these discussions are of interest to me.

I think Dave's personal choices with dil section and his overall bailout gas strategy are born of his experience and risk-tolerance, even perhaps physical abilities. We dive in mixed groups of OC/CCR divers, varying levels of experience and I feel the bailout gas I carry needs to be able to address this to a certain extent. I myself would just not be comfortable with such high PO2s even with short exposures. I tend to dive 1.2 ata on the bottom and am quite happy doing that. That said, putting the PO2 arguments aside, there are some very good reasons not to use 10/50 "all day long" that have been raised here.

In thinking about my own gas choices and the CCR I dive, on ascent with a 10/50 mix there are greater risks for bottoming out the PO2 nearer to the surface, but more so if your choice is to attempt semi-closed as a first option bailout approach, this gets problematic as you ascend (unless you bail-out OC onto a nitrox deco mix at some point). A gas like 20/50 seems like a decent choice up to 200 fsw and the math is still pretty easy for calculating PO2 on a dil flush at depth. This gas is a little more forgiving near the surface, especially if your CCR plumbs dil into the inhalation side of the rig as does mine (PRISM). Using 10/50 in a bailout scenario, I might chose to port in my off-board bailout gas (which should be something other than 10/50) through a LP QD hose into the first stage, shut off the onboard dil and go semi-closed with the bailout until I hit a depth I have OC deco gas for. Even during a normal ascent if I was concerned about breathing 10/50 at or near the surface for whatever reason, I could consider a redirect from my off-board bailout. All this just speaks to the relative risks of 10/50 for questionable gain doing dives where 10/50 may not be "required"... Food for thought.

Perhaps our former training in an OC setting (from EANx to Adv Trimix) stresses the risks of high PO2 such that we are ultra sensitive to it, but low PO2 risks really don't come into the picture in a meaningful way until CCR training. As such, maybe we under-appreciate the risks of low PO2 inherant in this gas choice as an "all the time" gas. In an OC setting, even using standard gases we are still best mixing for a range. In CCR diving it seems like its air dil or 10/50. I personally like the idea of using 20/50 for certain dives, but my depth limit would be much less than Dave's.

Heather Knowles

Depth-junkie · 3rd January 2007, 21:44

Good thread Dave

, even though i would not personaly use a hot mix for my dil. For OC bailout i have no probs in running 1.7pp regardles if OC or SCC as i am on my way up anyway.

I am in the 10/52 camp for ECCR i am afraid (i wont go into reason's as it's all been said before), along with OC bailout tanks (vol + gases dive dependant) with whips attached and reg's attached. As IMHO it gives me more options regarding bailout by being either OC all the way or semi closed with optimun PPO2 made available via whips on the stages which inturn give 2/3gases which can become available into the lungs/loop via man-inflators, much better than 1 hot mix dil IMHO (more options). I dont even notice my stages once i am in the water so i dont see them as a problem. But it's horses for courses, what works for you might not work for me and vice versa.

For me dil is dil and bailout is bailout, if you think Semi-closed is your No1 and only bailout stratergy fine, stick one or a couple of 3ltr's subject to depth onto your unit and run 2 hot mixes in them to plumb into your loop to pump up your PP02 in a bailout situation SCR, and your good to go.

I used to use a best mix stratergy for dil (target PP02 of 1-1.2PP) but it became a pain in the arse for remixes and also time spent in the dive shop getting fills. Now i just throw in 130bar helium top with air to 250bar and go diving, 10mins and i am in and out of the shop

40m-90m, no probs let go get wet.

As for all this talk of 10/52 in the shallows, if your that worried just isolate your ADV when you get to 6m. If your unit elecs are working it wont be a problem anyway, if it's not surely you will be on another gas or running a manuel 02 rebreather at this point dependant on your bailout choice.

Dave, i cannot agree with your method,but i can see where you are coming from in your method methology.

As i said good thread, it's thread's like this that get people thinking. And that can only be a good thing

My 10/52 dil is used purely for dil and inflating the wing and that's it. No more no less. If my diving was maxed out to 50-60m then your right no need to use a low F02 mix 18/40 would do the job or even 20/30, but it aint so for me 10/52 works

And I would be pissed off if i got refused access to a boat because of my dil selection.

ATB
Gareth

dive2dive2000 · 3rd January 2007, 22:18

Quote: (Originally Posted by NEwreckdiver)

Hi Dave and others -

I just wanted to say this has been a very interesting discussion that has given me a few things to think about. I realize now the discussion is caught up in the high PO2 issue, but that aside, I think Dave has some very valid points about diluent choice, especially in a bailout scenario where you may be going semi-closed. Personally I have never (yet) truly understood the reasoning for "10/50 all day long" on the CCR. I am admittedly a new rebreather diver and am still quite comfortable diving air diluent on <130 fsw dives, but every dive I do looks to the future when I will be using other gases and therefore these discussions are of interest to me.

I think Dave's personal choices with dil section and his overall bailout gas strategy are born of his experience and risk-tolerance, even perhaps physical abilities. We dive in mixed groups of OC/CCR divers, varying levels of experience and I feel the bailout gas I carry needs to be able to address this to a certain extent. I myself would just not be comfortable with such high PO2s even with short exposures. I tend to dive 1.2 ata on the bottom and am quite happy doing that. That said, putting the PO2 arguments aside, there are some very good reasons not to use 10/50 "all day long" that have been raised here.

In thinking about my own gas choices and the CCR I dive, on ascent with a 10/50 mix there are greater risks for bottoming out the PO2 nearer to the surface, but more so if your choice is to attempt semi-closed as a first option bailout approach, this gets problematic as you ascend (unless you bail-out OC onto a nitrox deco mix at some point). A gas like 20/50 seems like a decent choice up to 200 fsw and the math is still pretty easy for calculating PO2 on a dil flush at depth. This gas is a little more forgiving near the surface, especially if your CCR plumbs dil into the inhalation side of the rig as does mine (PRISM). Using 10/50 in a bailout scenario, I might chose to port in my off-board bailout gas (which should be something other than 10/50) through a LP QD hose into the first stage, shut off the onboard dil and go semi-closed with the bailout until I hit a depth I have OC deco gas for. Even during a normal ascent if I was concerned about breathing 10/50 at or near the surface for whatever reason, I could consider a redirect from my off-board bailout. All this just speaks to the relative risks of 10/50 for questionable gain doing dives where 10/50 may not be "required"... Food for thought.

Perhaps our former training in an OC setting (from EANx to Adv Trimix) stresses the risks of high PO2 such that we are ultra sensitive to it, but low PO2 risks really don't come into the picture in a meaningful way until CCR training. As such, maybe we under-appreciate the risks of low PO2 inherant in this gas choice as an "all the time" gas. In an OC setting, even using standard gases we are still best mixing for a range. In CCR diving it seems like its air dil or 10/50. I personally like the idea of using 20/50 for certain dives, but my depth limit would be much less than Dave's.

Heather Knowles

Hi Heather & Group

I too have found this thread extremely interesting and valuable. I had a total misunderstanding of Dave's point and an Alpinist view. What I once thought was totally irresponsible, reckless, and suicidal I now understand and respect. I have used 3 dils in my rig so far 21% 21/20 and 10/50. I used 10/50 on a dive to 180' my bail out gas was 21/35. I have the ability of an on-board plug in with its own shut off valve (should the need for SCR occur) I was taught that you should try and keep your dil no higher than 1.0/1.1 of deepest depth and 10% O2 is easy to mix and provides for simple math on dil flushes as does 21%. The only thing that I have done (or do) that is different from training is I added this isolator valve to my dil line(I guess I am a NAUI/PRISM Alpinist).

I have done this for a few reasons:
A) With 10/50 I don't want any F-ups (in shallow water) so my dil is off with out shutting my tank valve still have access to wing inflation if needed.
B) I like pure O2 on descent to 20', and I breath down to set point (no chance of ADV going off)
C) I like pure O2 on ascent and don't want any more HE after 20'(no chance of ADV going off)
D) If my ADV fails I can isolate it and not loose wing inflation.

My OC bail out is always at 1.4 (and set up so my rig can use it in SCR mode).

I would like to see a separate manual plug in for dil besides the ADV and then I feel my rig is complete.

With reading between Dave's lines and realizing he posted ultra ultra extreme limits to make his point, our training and thinking is not that far off

My instructor has pointed out numerous times as hrs and ability increases Tasks and protocols will change, what does not seem prudent now, might be standard operating procedure tomorrow.

CharlieT · 4th January 2007, 17:30

Quote: (Originally Posted by Decodiver)

Gottya..........

He must have seen you coming

Charlie

Tom Mount · 6th January 2007, 23:22

Hi Dave
I really do not think you can give me a spanking- so if I show up with 10 50 dill which I use a lot of the time and if I just missed a 250 which is the gas I would use at that depth for sure and the next dive was 130 I would gladly use my 10 50- one I do not bailout to my on board dil so my off board bailout would most likely be a 32 something and if I had to go SCR I would plug in my off board bailout cylinder to do so

And I think anyone running a dil with 1.8 po2 is highly insane-
1. It makes the po2 you are breathing on the dive to high
2. You cannot flush down if a solenoid fails open
3. You have a high probability of toxing if you are doing exercise as has been proven by divers dying at those po2's

as a bailout where an immediate ascent is available it may be worth considering but for me 1.6 is high enough if direct ascent is possible other wise my bailout is 1.4 so can be used in Variable Semi Closed very effectively and I always keep my on board dil at a max of around 1.0 so I can flush the unit down if need be
Just not quite as tough as you but then I also carry bailout that will get me up on OC if needed and it really does not take much from a 250 or so wreck diving usually a 40 for ascent then a 50 which is another 40 although sometime I carry a 15 cube o2 (30 minutes or more on deco at 20 ft) and if on Meg can use o2 open loop bailout thus have access to the remaining oxygen in the unit

My typical starting dil are as follows bit I bump them up with other gases such as a 10 50 at 2000 psi may bump up with a 20 35 or air or a 20 35 at 2000 may bump up with 10 50 or 8 60 so my dils will vary as to content

But these are my personal typical stat up dil mixes

20 35
10 50
8 60
6 70

Air rarely and only if I have bumped up the dil to a point that almost no He is in them

Start the dive with somewhere between .7 and 1/0 drop fast on once volume is established on bottom close shut off valve so dil is not used except if actually needed fro volume or flushing ascend with dil off unless for some reason it is need usually fly 1.2 on deeper dives deco 1.3 to 1.4

Shallow dives use such 40 to 70 ft use .8 to 1.0 unless getting close to deco then bring po2 up slowly to as high as 1.2 for dive

Most of the time set the set point at 1.0 or 1.1 and manually maintain the 1.2

At 67 and diving since 1957 ( in March 50 years of diving and 59 years of martial arts and I get in the ring with my students there as well) my goal is to be the oldest diver still doing good dives - so I do not play with high po2's lucked out when I was young by surviving all the deep air dives and oxygen deco starting at 30 feet sometime 40 so have used enough of my allotted lives not to gamble them now on something that does not provide any real benefit such as high po2

Tom Mount · 6th January 2007, 23:52

Quote: (Originally Posted by dave sutton)

We ought to get Tom Mount here for a history lesson. He knows the players and the details better than I do. 1.2 PP02? That was a political decision to bring "mix gas to the masses" and to MAKE MONEY, nothing more. The problem now is that "we" as technical divers (not me, BTW), were trained AFTER THIS TIME and since we were taught that "High PP02 will *kill you*" we actually BELIEVE it. Hey, our instrucotr SAID SO, right? And it's in this BOOK.... so it must be right. It works, so it MUST be right... (hmmm.... but then again.................)

OK, it's right. Carry all that crap... you'are a customer and DEMA members want that money...

Dave

Hi dave

The USN does not usually use extreme exposure limits- least not when I was in except for emergencies.

Now also remember on oxygen CCR 20 feet is not a steady 1.6 but more like 1.4 even if you do purge the loop several times before using the unit operationally thus the ability to go deeper

When I started standard (not exceptional exposure) po2 was 2.0 then due to accidents was reduced to 1.8 then to 1.6 and I do not know of any reason to reduce max based on duration to less than 1.6 on CCr I think 1.2 is a good max for longer or deeper dives due again to duration
And the oxygen clock had its foundations from the work of Donald who wrote a 20 year plus history of oxygen incidents and numerous physiologists expanded this work into a clock -

When one reaches 100% of the clock it is believed they enter a risk zone to some degree not sudden convulsions as some do believe

And new factors such as optical myopia have presented them selves with cCR so it is wise to keep po2 at levels they are actually needed not just a given set point if you dive at 60 feet then use a 08 or so as there is no real advantage of a higher po2 at deeper depths balance po2 and deco -you will find a high bottom po2 gains you very little in run time on CCR and provides much more risk- so save higher po2 for deco when you are at basil metabolic rate

Morgan Wells actualy kicked off Nitrox to NOAA and Dick Rutkowski introduced it to recreational diving

I think po2 issues are very importan ton CCR due to duration and CO2 production- also think there is even more advantage for higher he on CCR due to co2 production

And we should all be aware from EDU studines there is a huge variation inCO2 production amoung divers as well as toxing and deco issues

A canister rated at 3 hours may last a diver in gfood shape who is very relaxed inthe water and has alow metabolic rate 6 hours the same canister with someone with a larger tidal volume and faster metabolism may last less than 2 hours- some retainers exceed maximin level before getting intot he water
The israeli Navy actually test military CCR divers for co2 production and eliminate the co2 retainers from diving ccr

On bailout oit really does not take that much to safely bailout many divers carry excessive bailout and others way to little- I feel any cCR dive should have adequate bailout to surface- and the only way to really lknow is to do some bailouts from depth on real dives - then you can accurately predict the gas needed and also be more relaxed in an emergency as you know how much gas from a practical point not just working a formula- most of us use less than the math reflects unless someone alows stress to overcome them- again a good reason to doreal practice is the likely hood of giving in to stress is less if you actually know what you need- plan gas based on buddy team

tom

**Dave Sutton** · 7th January 2007, 02:40

If the thread did nothing else but to lure out an old friend, it was worth it. Welcome aboard! And you're right, I'd never spank an old man. Come up and dive the U-853 with us this summer. Your money is no good aboard EXPLORER so come and dive. We'll even feed you.

Best to you, and great to see you here.

Dave Sutton (Happy with 20/50 these days)

SteveL · 7th January 2007, 12:40

Quote: (Originally Posted by jradomski)

Dave, There are several things that will effect the actual po2.. FIrst off the loop volume and second descent speed.. I did a best guess.. The best you could ever do (maintaining optimal volume) is if you used up all the o2 from the surface on descent, and that would be a 2.0, so a very slow descent can reach this.. The only way you could do better than this is to have a volume during descent that is much larger than you need and have enough left over so that its near what you need at target depth.. This way your slow descent helps you burn up additional oxygen that isn't being replaced by adding dil to maintain volume..

The numbers I ran was for a loop that was totall mixed and prebreathed on the surface.. If it was just allowed to go up to .7, there would be alot less oxygen..

Well for what its worth...

I dive a Mk 15.5

But mount a 5l for nearly all dives up to about 55m this is all the bailout I carry - it is pumped full of air and can be switched inboard if necessary by turning one knob.

Onboard Dil to these depths is usually 21/33He

Like Dave I am fastidious about loop integrity and unit functionality.

I test the cells regularly in a pot.

I do not believe in Rebreather electronics doing ANYTHING other then controlling setpoint.

I generally turn my unit on at the surface pump some 02 in until I am around 60% on the boat - jump in and I am confident that if I have to fight the current to the line im not going hypoxic even if the ADV kicks in

On a regular normal decent my unit is addid 02 as I decend as it most likely wont be at setpoint (I usually run at 1.2) and ther ADV will be addid dill.

I can probably count on one hand the number of times I have got the PP02 over 1.6 by the time I hit the bottom using this method.

Personally I like a slow decent so I dont get puffed, time to get thing sorted and gives the scrubber some time to get warm.

Seems to work OK for me.

Obviously much deeper than this and I carry a sling and do change the onboard dil. Generally the 5l butt mount is still full of air.

Alot of people wont agree with this but hey Im not telling you how to dive just the way I do it - and like Dave I am a big fan of keeping things simple and uncluttered.

My 2c worth.

Steve L

3rd January 2007, 01:15	#101 (permalink)
Simon Mitchell New Member Current Rebreather/s: MK 15.X Other Rebreather/s: Join Date: May 2005 Location: New Zealand Posts: 201	Re: Diluent selection and the great alpinist v siege debate Quote: (Originally Posted by jradomski) Hi Dave, There have been a few studies (more is needed) that different inert gases effect our resistance to oxygen issues.. Evidence suggests Helium increases our likelihood for a problem while N2 reduces it.. So if we make the breathing easier we increase our risk by the inert gas but lower co2 retention, if we have alot of n2 we reduce our risk by the po2 but increase our risk due to co2 retention.. .. Hello Joe, Can you please point me in the direction of this evidence?? Thanks, Simon M
(Online)

3rd January 2007, 19:49	#103 (permalink)
NEwreckdiver RBW Member Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Oct 2005 Location: Boston MA Posts: 84	Re: Diluent selection and the great alpinist v siege debate Hi Dave and others - I just wanted to say this has been a very interesting discussion that has given me a few things to think about. I realize now the discussion is caught up in the high PO2 issue, but that aside, I think Dave has some very valid points about diluent choice, especially in a bailout scenario where you may be going semi-closed. Personally I have never (yet) truly understood the reasoning for "10/50 all day long" on the CCR. I am admittedly a new rebreather diver and am still quite comfortable diving air diluent on <130 fsw dives, but every dive I do looks to the future when I will be using other gases and therefore these discussions are of interest to me. I think Dave's personal choices with dil section and his overall bailout gas strategy are born of his experience and risk-tolerance, even perhaps physical abilities. We dive in mixed groups of OC/CCR divers, varying levels of experience and I feel the bailout gas I carry needs to be able to address this to a certain extent. I myself would just not be comfortable with such high PO2s even with short exposures. I tend to dive 1.2 ata on the bottom and am quite happy doing that. That said, putting the PO2 arguments aside, there are some very good reasons not to use 10/50 "all day long" that have been raised here. In thinking about my own gas choices and the CCR I dive, on ascent with a 10/50 mix there are greater risks for bottoming out the PO2 nearer to the surface, but more so if your choice is to attempt semi-closed as a first option bailout approach, this gets problematic as you ascend (unless you bail-out OC onto a nitrox deco mix at some point). A gas like 20/50 seems like a decent choice up to 200 fsw and the math is still pretty easy for calculating PO2 on a dil flush at depth. This gas is a little more forgiving near the surface, especially if your CCR plumbs dil into the inhalation side of the rig as does mine (PRISM). Using 10/50 in a bailout scenario, I might chose to port in my off-board bailout gas (which should be something other than 10/50) through a LP QD hose into the first stage, shut off the onboard dil and go semi-closed with the bailout until I hit a depth I have OC deco gas for. Even during a normal ascent if I was concerned about breathing 10/50 at or near the surface for whatever reason, I could consider a redirect from my off-board bailout. All this just speaks to the relative risks of 10/50 for questionable gain doing dives where 10/50 may not be "required"... Food for thought. Perhaps our former training in an OC setting (from EANx to Adv Trimix) stresses the risks of high PO2 such that we are ultra sensitive to it, but low PO2 risks really don't come into the picture in a meaningful way until CCR training. As such, maybe we under-appreciate the risks of low PO2 inherant in this gas choice as an "all the time" gas. In an OC setting, even using standard gases we are still best mixing for a range. In CCR diving it seems like its air dil or 10/50. I personally like the idea of using 20/50 for certain dives, but my depth limit would be much less than Dave's. Heather Knowles
(Offline)

3rd January 2007, 21:44	#104 (permalink)
Depth-junkie 10/52 Psycho Current Rebreather/s: Inspiration Vision Other Rebreather/s: Join Date: Aug 2005 Location: Wrexham Posts: 300	Re: Diluent selection and the great alpinist v siege debate Good thread Dave , even though i would not personaly use a hot mix for my dil. For OC bailout i have no probs in running 1.7pp regardles if OC or SCC as i am on my way up anyway. I am in the 10/52 camp for ECCR i am afraid (i wont go into reason's as it's all been said before), along with OC bailout tanks (vol + gases dive dependant) with whips attached and reg's attached. As IMHO it gives me more options regarding bailout by being either OC all the way or semi closed with optimun PPO2 made available via whips on the stages which inturn give 2/3gases which can become available into the lungs/loop via man-inflators, much better than 1 hot mix dil IMHO (more options). I dont even notice my stages once i am in the water so i dont see them as a problem. But it's horses for courses, what works for you might not work for me and vice versa. For me dil is dil and bailout is bailout, if you think Semi-closed is your No1 and only bailout stratergy fine, stick one or a couple of 3ltr's subject to depth onto your unit and run 2 hot mixes in them to plumb into your loop to pump up your PP02 in a bailout situation SCR, and your good to go. I used to use a best mix stratergy for dil (target PP02 of 1-1.2PP) but it became a pain in the arse for remixes and also time spent in the dive shop getting fills. Now i just throw in 130bar helium top with air to 250bar and go diving, 10mins and i am in and out of the shop 40m-90m, no probs let go get wet. As for all this talk of 10/52 in the shallows, if your that worried just isolate your ADV when you get to 6m. If your unit elecs are working it wont be a problem anyway, if it's not surely you will be on another gas or running a manuel 02 rebreather at this point dependant on your bailout choice. Dave, i cannot agree with your method,but i can see where you are coming from in your method methology. As i said good thread, it's thread's like this that get people thinking. And that can only be a good thing My 10/52 dil is used purely for dil and inflating the wing and that's it. No more no less. If my diving was maxed out to 50-60m then your right no need to use a low F02 mix 18/40 would do the job or even 20/30, but it aint so for me 10/52 works And I would be pissed off if i got refused access to a boat because of my dil selection. ATB Gareth Last edited by Depth-junkie : 3rd January 2007 at 22:04. Reason: added a bit
(Offline)

3rd January 2007, 22:18	#105 (permalink)
dive2dive2000 PRISM DIVER & LUVIN IT! Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Feb 2005 Location: Long Island, NY Posts: 798	Re: Diluent selection and the great alpinist v siege debate Quote: (Originally Posted by NEwreckdiver) Hi Dave and others - I just wanted to say this has been a very interesting discussion that has given me a few things to think about. I realize now the discussion is caught up in the high PO2 issue, but that aside, I think Dave has some very valid points about diluent choice, especially in a bailout scenario where you may be going semi-closed. Personally I have never (yet) truly understood the reasoning for "10/50 all day long" on the CCR. I am admittedly a new rebreather diver and am still quite comfortable diving air diluent on <130 fsw dives, but every dive I do looks to the future when I will be using other gases and therefore these discussions are of interest to me. I think Dave's personal choices with dil section and his overall bailout gas strategy are born of his experience and risk-tolerance, even perhaps physical abilities. We dive in mixed groups of OC/CCR divers, varying levels of experience and I feel the bailout gas I carry needs to be able to address this to a certain extent. I myself would just not be comfortable with such high PO2s even with short exposures. I tend to dive 1.2 ata on the bottom and am quite happy doing that. That said, putting the PO2 arguments aside, there are some very good reasons not to use 10/50 "all day long" that have been raised here. In thinking about my own gas choices and the CCR I dive, on ascent with a 10/50 mix there are greater risks for bottoming out the PO2 nearer to the surface, but more so if your choice is to attempt semi-closed as a first option bailout approach, this gets problematic as you ascend (unless you bail-out OC onto a nitrox deco mix at some point). A gas like 20/50 seems like a decent choice up to 200 fsw and the math is still pretty easy for calculating PO2 on a dil flush at depth. This gas is a little more forgiving near the surface, especially if your CCR plumbs dil into the inhalation side of the rig as does mine (PRISM). Using 10/50 in a bailout scenario, I might chose to port in my off-board bailout gas (which should be something other than 10/50) through a LP QD hose into the first stage, shut off the onboard dil and go semi-closed with the bailout until I hit a depth I have OC deco gas for. Even during a normal ascent if I was concerned about breathing 10/50 at or near the surface for whatever reason, I could consider a redirect from my off-board bailout. All this just speaks to the relative risks of 10/50 for questionable gain doing dives where 10/50 may not be "required"... Food for thought. Perhaps our former training in an OC setting (from EANx to Adv Trimix) stresses the risks of high PO2 such that we are ultra sensitive to it, but low PO2 risks really don't come into the picture in a meaningful way until CCR training. As such, maybe we under-appreciate the risks of low PO2 inherant in this gas choice as an "all the time" gas. In an OC setting, even using standard gases we are still best mixing for a range. In CCR diving it seems like its air dil or 10/50. I personally like the idea of using 20/50 for certain dives, but my depth limit would be much less than Dave's. Heather Knowles Hi Heather & Group I too have found this thread extremely interesting and valuable. I had a total misunderstanding of Dave's point and an Alpinist view. What I once thought was totally irresponsible, reckless, and suicidal I now understand and respect. I have used 3 dils in my rig so far 21% 21/20 and 10/50. I used 10/50 on a dive to 180' my bail out gas was 21/35. I have the ability of an on-board plug in with its own shut off valve (should the need for SCR occur) I was taught that you should try and keep your dil no higher than 1.0/1.1 of deepest depth and 10% O2 is easy to mix and provides for simple math on dil flushes as does 21%. The only thing that I have done (or do) that is different from training is I added this isolator valve to my dil line(I guess I am a NAUI/PRISM Alpinist). I have done this for a few reasons: A) With 10/50 I don't want any F-ups (in shallow water) so my dil is off with out shutting my tank valve still have access to wing inflation if needed. B) I like pure O2 on descent to 20', and I breath down to set point (no chance of ADV going off) C) I like pure O2 on ascent and don't want any more HE after 20'(no chance of ADV going off) D) If my ADV fails I can isolate it and not loose wing inflation. My OC bail out is always at 1.4 (and set up so my rig can use it in SCR mode). I would like to see a separate manual plug in for dil besides the ADV and then I feel my rig is complete. With reading between Dave's lines and realizing he posted ultra ultra extreme limits to make his point, our training and thinking is not that far off My instructor has pointed out numerous times as hrs and ability increases Tasks and protocols will change, what does not seem prudent now, might be standard operating procedure tomorrow. __________________ Safe Diving, Martin
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4th January 2007, 17:30	#106 (permalink)
CharlieT RBW Member Current Rebreather/s: Inspiration Vision Other Rebreather/s: Join Date: Nov 2005 Location: London Posts: 450	Re: ad_ward9 slamming everyone elses gear Quote: (Originally Posted by Decodiver) Gottya.......... He must have seen you coming Charlie
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6th January 2007, 23:22	#107 (permalink)
Tom Mount New Member Current Rebreather/s: Inspiration Classic Evolution Megalodon Sport Kiss Classic Kiss Optima Other CCR Other Rebreather/s: Other CCR Join Date: Jul 2005 Location: USA Posts: 95	Re: Diluent selection and the great alpinist v siege debate Hi Dave I really do not think you can give me a spanking- so if I show up with 10 50 dill which I use a lot of the time and if I just missed a 250 which is the gas I would use at that depth for sure and the next dive was 130 I would gladly use my 10 50- one I do not bailout to my on board dil so my off board bailout would most likely be a 32 something and if I had to go SCR I would plug in my off board bailout cylinder to do so And I think anyone running a dil with 1.8 po2 is highly insane- 1. It makes the po2 you are breathing on the dive to high 2. You cannot flush down if a solenoid fails open 3. You have a high probability of toxing if you are doing exercise as has been proven by divers dying at those po2's as a bailout where an immediate ascent is available it may be worth considering but for me 1.6 is high enough if direct ascent is possible other wise my bailout is 1.4 so can be used in Variable Semi Closed very effectively and I always keep my on board dil at a max of around 1.0 so I can flush the unit down if need be Just not quite as tough as you but then I also carry bailout that will get me up on OC if needed and it really does not take much from a 250 or so wreck diving usually a 40 for ascent then a 50 which is another 40 although sometime I carry a 15 cube o2 (30 minutes or more on deco at 20 ft) and if on Meg can use o2 open loop bailout thus have access to the remaining oxygen in the unit My typical starting dil are as follows bit I bump them up with other gases such as a 10 50 at 2000 psi may bump up with a 20 35 or air or a 20 35 at 2000 may bump up with 10 50 or 8 60 so my dils will vary as to content But these are my personal typical stat up dil mixes 20 35 10 50 8 60 6 70 Air rarely and only if I have bumped up the dil to a point that almost no He is in them Start the dive with somewhere between .7 and 1/0 drop fast on once volume is established on bottom close shut off valve so dil is not used except if actually needed fro volume or flushing ascend with dil off unless for some reason it is need usually fly 1.2 on deeper dives deco 1.3 to 1.4 Shallow dives use such 40 to 70 ft use .8 to 1.0 unless getting close to deco then bring po2 up slowly to as high as 1.2 for dive Most of the time set the set point at 1.0 or 1.1 and manually maintain the 1.2 At 67 and diving since 1957 ( in March 50 years of diving and 59 years of martial arts and I get in the ring with my students there as well) my goal is to be the oldest diver still doing good dives - so I do not play with high po2's lucked out when I was young by surviving all the deep air dives and oxygen deco starting at 30 feet sometime 40 so have used enough of my allotted lives not to gamble them now on something that does not provide any real benefit such as high po2
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6th January 2007, 23:52	#108 (permalink)
Tom Mount New Member Current Rebreather/s: Inspiration Classic Evolution Megalodon Sport Kiss Classic Kiss Optima Other CCR Other Rebreather/s: Other CCR Join Date: Jul 2005 Location: USA Posts: 95	Re: Diluent selection and the great alpinist v siege debate Quote: (Originally Posted by dave sutton) We ought to get Tom Mount here for a history lesson. He knows the players and the details better than I do. 1.2 PP02? That was a political decision to bring "mix gas to the masses" and to MAKE MONEY, nothing more. The problem now is that "we" as technical divers (not me, BTW), were trained AFTER THIS TIME and since we were taught that "High PP02 will kill you" we actually BELIEVE it. Hey, our instrucotr SAID SO, right? And it's in this BOOK.... so it must be right. It works, so it MUST be right... (hmmm.... but then again.................) OK, it's right. Carry all that crap... you'are a customer and DEMA members want that money... Dave Hi dave The USN does not usually use extreme exposure limits- least not when I was in except for emergencies. Now also remember on oxygen CCR 20 feet is not a steady 1.6 but more like 1.4 even if you do purge the loop several times before using the unit operationally thus the ability to go deeper When I started standard (not exceptional exposure) po2 was 2.0 then due to accidents was reduced to 1.8 then to 1.6 and I do not know of any reason to reduce max based on duration to less than 1.6 on CCr I think 1.2 is a good max for longer or deeper dives due again to duration And the oxygen clock had its foundations from the work of Donald who wrote a 20 year plus history of oxygen incidents and numerous physiologists expanded this work into a clock - When one reaches 100% of the clock it is believed they enter a risk zone to some degree not sudden convulsions as some do believe And new factors such as optical myopia have presented them selves with cCR so it is wise to keep po2 at levels they are actually needed not just a given set point if you dive at 60 feet then use a 08 or so as there is no real advantage of a higher po2 at deeper depths balance po2 and deco -you will find a high bottom po2 gains you very little in run time on CCR and provides much more risk- so save higher po2 for deco when you are at basil metabolic rate Morgan Wells actualy kicked off Nitrox to NOAA and Dick Rutkowski introduced it to recreational diving I think po2 issues are very importan ton CCR due to duration and CO2 production- also think there is even more advantage for higher he on CCR due to co2 production And we should all be aware from EDU studines there is a huge variation inCO2 production amoung divers as well as toxing and deco issues A canister rated at 3 hours may last a diver in gfood shape who is very relaxed inthe water and has alow metabolic rate 6 hours the same canister with someone with a larger tidal volume and faster metabolism may last less than 2 hours- some retainers exceed maximin level before getting intot he water The israeli Navy actually test military CCR divers for co2 production and eliminate the co2 retainers from diving ccr On bailout oit really does not take that much to safely bailout many divers carry excessive bailout and others way to little- I feel any cCR dive should have adequate bailout to surface- and the only way to really lknow is to do some bailouts from depth on real dives - then you can accurately predict the gas needed and also be more relaxed in an emergency as you know how much gas from a practical point not just working a formula- most of us use less than the math reflects unless someone alows stress to overcome them- again a good reason to doreal practice is the likely hood of giving in to stress is less if you actually know what you need- plan gas based on buddy team tom Last edited by EBT : 7th January 2007 at 00:20. Reason: fixing the quotes
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7th January 2007, 02:40	#109 (permalink)
Dave Sutton Diveshop of Horrors Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Evolution Megalodon rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,971	Re: Diluent selection and the great alpinist v siege debate If the thread did nothing else but to lure out an old friend, it was worth it. Welcome aboard! And you're right, I'd never spank an old man. Come up and dive the U-853 with us this summer. Your money is no good aboard EXPLORER so come and dive. We'll even feed you. Best to you, and great to see you here. Dave Sutton (Happy with 20/50 these days) __________________ "Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com And the colors of the sea blind your eyes with trembling mermaids, For the sparkling waves are calling you to kiss their white-laced lips. And you see a girls brown body dancing through the turquoise, And her footprints make you follow where the sky loves the sea. And when your fingers find her, she drowns you in her body, Carving deep blue ripples in the tissues of your mind...... Last edited by Dave Sutton : 7th January 2007 at 02:44.
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7th January 2007, 12:40	#110 (permalink)
SteveL RBW Member Current Rebreather/s: MK 15.X Other Rebreather/s: Inspiration Classic Join Date: Nov 2005 Location: Sydney Australia Posts: 224	Re: Diluent selection and the great alpinist v siege debate Quote: (Originally Posted by jradomski) Dave, There are several things that will effect the actual po2.. FIrst off the loop volume and second descent speed.. I did a best guess.. The best you could ever do (maintaining optimal volume) is if you used up all the o2 from the surface on descent, and that would be a 2.0, so a very slow descent can reach this.. The only way you could do better than this is to have a volume during descent that is much larger than you need and have enough left over so that its near what you need at target depth.. This way your slow descent helps you burn up additional oxygen that isn't being replaced by adding dil to maintain volume.. The numbers I ran was for a loop that was totall mixed and prebreathed on the surface.. If it was just allowed to go up to .7, there would be alot less oxygen.. Well for what its worth... I dive a Mk 15.5 But mount a 5l for nearly all dives up to about 55m this is all the bailout I carry - it is pumped full of air and can be switched inboard if necessary by turning one knob. Onboard Dil to these depths is usually 21/33He Like Dave I am fastidious about loop integrity and unit functionality. I test the cells regularly in a pot. I do not believe in Rebreather electronics doing ANYTHING other then controlling setpoint. I generally turn my unit on at the surface pump some 02 in until I am around 60% on the boat - jump in and I am confident that if I have to fight the current to the line im not going hypoxic even if the ADV kicks in On a regular normal decent my unit is addid 02 as I decend as it most likely wont be at setpoint (I usually run at 1.2) and ther ADV will be addid dill. I can probably count on one hand the number of times I have got the PP02 over 1.6 by the time I hit the bottom using this method. Personally I like a slow decent so I dont get puffed, time to get thing sorted and gives the scrubber some time to get warm. Seems to work OK for me. Obviously much deeper than this and I carry a sling and do change the onboard dil. Generally the 5l butt mount is still full of air. Alot of people wont agree with this but hey Im not telling you how to dive just the way I do it - and like Dave I am a big fan of keeping things simple and uncluttered. My 2c worth. Steve L
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