Diluent selection and the great alpinist v siege debate

Dave Sutton · 30th December 2006, 23:27

Quote: (Originally Posted by Doorduijn, Niels)

Interesting debate.

As a side-comment, for those of you with DAN insurance, and a desire to keep the coverage in place, be aware that under the DAN Europe insurance, the max PpO2 on a technical dive is is 1.4, otherwise the dive is not covered.

Rgs,
Niels Doorduijn

My friend Bill Hamillton, DAN's spiritual founder, would cry if he heard this. You would think that DAN would be happy to have people *less* likely to get DCS, no? Desk-bound bean counters and shoe-clerks running huge paper feifdoms can go stuff themselves. That's right up with the CE. Thank God I live in the CE-Free good old USA where a man can actually buy the worlds safest rebreather, the KISS ....

In any case, carrying hot diluent does NOT mean you are *diving* a hot mix. Unlike open circuit, you can CARRY 1.6, 1.8, 2.0 as diluent and DIVE 1.4... I do it all the time. Let the lawyers argue about that. They deserve what they get. Tell you what, I'll testify as an expert at any civil trial after they deny coverage. Bet I win too.

Dave Sutton

**Steve** · 30th December 2006, 23:37

Quote: (Originally Posted by EBT)

Thats not what I asked though is it dave. The point I was making is that your technique is REQUIRED because you dive alpinist. Someone with OC bailout may choose different techniques since they have an additional tool in the armoury. You have to look at the circumstances to be sure you're being appropriate and avoiding IACDT (as you put it).

Personally, my dil at its richest runs to 1.3 PO2, normally its 1.0. My reasons;

1. it provides an effective flush DOWN
2. despite USN limits etc, the world has based their O2 limits on kenneth mcdonalds work and his conlusions were essentially that O2 is unpredictable even within the same individual. I dont want to push that.
3. In an emergency, theres a good chance of elevated adrenaline and a possibility of elevated CO2. Both of those are bad ideas with high O2.

one thing we do agree on... hypoxia is serious and immediate, hyperoxia is not quite as serious and definitely not as immediate.

I do welcome the alternate views though, it never hurts to understand and consider other approaches.

/Z

I couldn't agree more Zak. Whilst understanding Dave's point I couldn't disagree with his beliefs on this issue more strenuously if I tried. I just can't get the cold hard fact that every rebreather diver that I knew personally that is no longer with us died from either one or a combination of 4 things;

Inadequate bailout volume. They needed more gas.
Hyperoxia and then drowning
No buddy to help out and fix a small issue that snowballed
Skill deficit. They made a simple mistake and they should have known better

I feel compelled to learn from their deaths.

This topic should get it's own thread IMO

Dave Sutton · 30th December 2006, 23:44

[quote=Steve;86570]IHyperoxia and then drowning

Wait a minute: You actually *know* of a death caused by *high* PP02 on a rebreather? Do tell us all about it. All of the dead friends of mine that have died on rebreathers (and there are more than I have fingers on one hand) died due to low PP02. I know of a total of zero divers that have toxed on a rebreather and that's including many hundreds hours of seeing guys dive at 40 feet on the LAR-V as well as my own diving the LAR-V as well as running 1.6 as our *normal* mix as a commercial diver for *thousands* of hours.

Forget the bailout thing, totally divorce it from the diluent selection discussion as the two are not the same. Is there *any* reason to select surface-hypoxic mixes if they are not *required* for the depth planned, or any rationale to select mix where the PP02 of the diluent is not at *least* equal to the desired PP02 at the desired depth? Forget "greater" than the setpoint PP02, use the term "at least" and start writing. Love to hear all about it.

Best,

Dave

dive2dive2000 · 31st December 2006, 00:00

Quote: (Originally Posted by Dave Sutton)

I respectfully disagree. Pick a depth: I'll pick 250 feet. Deep enough to be deep but not scary deep:

21% diluent = 1.8 PP02

US Navy LAR-V 02 limits for 1.8 PP02 = *essentially infinite duration* (IE: 240 minutes, or *4 hours*)

If I flush my loop with diluent at 250 using that mix it'll be *leaned out* to 1.4 in about *4 minutes*..... (and note that the time base for this "burn off" changes with loop volume, if you purge to CLVmin <Definition: counterlung volume minimum, volume = tidal volume> it'll slide down faster than if you inject more gas into the counterlung)

Let's see, that's an hour of time available against each minute of time used... I'll take that bet!

Bottom line is that there is *utterly no reason* to EVER dive a mix leaner that 21% shallower than 250 feet.

Let's take it to the boolean logic string:

(1): There is *no way in hell* I'll get hurt with that mix *ever* as the time spent on that mix at depth is *either open circuit in which case I'm blowing thru it fast* or closed circuit *where I am decreasing the PP02 fraction thru metabolism* is *FAR shorter* than the time it would take to even come close to acute 02 tox time. And by meaning FAR SHORTER I'm talking *hours* at 250 feet.

AND

(2): I can use it as a VERY EFFICIENT SCC mix for bailout modes.

AND

(3): It is FAR BETTER as a basic deco mix either SCC or Open Circuit than a 10% mix.

AND

(4): The alternatively proposed 10% mix is LETHAL near the surface in SECONDS.

AND

(5): 10% makes a poor choice for a SCC gas for "on loop" bailout in case ya'll loose your 02 for some reason.

AND

(6): 10% dil makes a *piss poor* deco gas open circuit.

THUS

(7): Thus there is *no rationale* for using a 10% mix for this dive. None. No how. No way. Zero. Nada. Zippo.

END

That's not opinion, it's fact.... makes no difference if you carry bailout or not. 10% dil selection for this sort of dive is *just plain wrong* and I don't care who teaches that it's OK. They are wrong.

The only operational issue with this mix is that you need to purge the loop once on descent (or after reaching bottom), assuming that you allowed the loop to go to higher than 0.21 on the surface. I'll take on that workload in return for the advantages. With my Mark-15 it's easy as I jump in with the rig turned off and it's not trying to inject 02 until I turn it on. I don't turn it on until I hit the bottom anyhow. Makes my purge depth irrelevant. If you dive a rig with "auto-on" power, purge after your depth = your depth for setpoint = diluent PP02 at that depth, assuming that you are diving deeper than where PP02 (setpoint) = PP02 (diluent).

Educated Opinion: Where the dive training industry has *gone wrong* is that it has TOTALLY failed to distinguish in training between the HUGE time difference (MANY orders of magnitude) between the time it takes to have a problem due to high PP02 versus low PP02.

This is what I teach:

(1): *Respect* high PPO2 and do something about it *In good time*.

(2): FEAR low PP02 'cause it's gonna kill you *RIGHT FRIGGIN' NOW*.

Oxygen is life. Fear the gas that carries little.

Dave

I am a little confused at your reasoning. I was taught (and in all honesty it does make sense) that a rebreather is nothing more than a mixing station on your back. You sorta have an open circuit best mix mentality.

What about your OTU's. Doing multi day diving between 1.4 and 1.8 does have disadvantages too. While we probably will never come close to OTU limits; do say 3 hrs a day from 1.4 to 1.8 and need a chamber ride on the 3rd day there is a good chance they wont admit you. Right wrong or indifferent that is the way it is.

There is always the whole picture and not just a small piece of the puzzle when considering a dive plan, and your prior posts suggested that when it came to buddy diving /solo diving cave diving techniques... different circumstances depend on procedure.

I feel 10% is a good mix for dives deeper than 150' for a few reasons I can keep a gas at 1 to 1.3, I can easily do a flush and bring down an elevated PPO2, and I can do multi day diving and still keep my OTU's at a manageable level if god forbid I need a chamber ride. And you said it best in another post "Dr. Hamilton is gonna cry when he reads this" More like scream and cuss is a better analogy

**Steve** · 31st December 2006, 00:11

Alpinist V's OC bailout discussion successfully parked

'Selecting surface-hypoxic mixes if they are not required for the depth planned' is agreed as well.

PP02 of the diluent at least equal to the desired PP02 at the desired depth. This is the bit I don't like. Like you I have a LAR V background and whilst none of my Navy mates died from tox issues. I have seen enough incidents to warrant caution in my recreational diving as my civilian buddies don't look after my back the way a Navy dive team member does.

Moving away from O2 CCRs, taking the ability to do a cell verification or drop the pO2 away from a diver is an unnecessary risk. Cells are the weakest part of every rebreather out there and I like every tool possible in verifying them. I plan my dil to be 0.1 lower than my planned pO2 for the max depth of the dive. Dud sensor info can be cross checked this way.

Also, if the dil has a higher than planned diving pO2 and there is an O2 leak, solenoid jam etc you are forced to breath it down. Fine if one can ascend granted but a bit too much pucker factor if it isn't a option for a while

Fred Evans fitted and drowned. His sensors were current limited so his pO2 was higher than he believed it to be.

Dave Sutton · 31st December 2006, 00:11

Quote: (Originally Posted by dive2dive2000)

II feel 10% is a good mix for dives deeper than 150' for a few reasons I can keep a gas at 1 to 1.3,

Dude:

At 150 feet, 21% mix is *1.1* PP02. That's 0.1 LESS than a sort of normal 1.2 PP02 setpoint. Why in the world would you want your diluent to be LESS THAN HALF of your target setpoint? I mean, heck: Why don't you just dive *pure inert gas* as your diluent? Your 10% at 150 feet is doing you about as much good. Don't you WANT to be able to breathe that gas at the surface if you can?

Yes, a rebreather is a "gas mixing station on your back". What instructors apparently are failing to teach is that not only can you RAISE a low PP02 mix to a good mix by ADDING 02, you can also LOWER a "slightly" rich mix to a good one *in a time period that you can ignore for all practical purposes* by REMOVING 02. You RAISE PP02 with a push button or a solenoid vave. You REMOVE 02 by BREATHING for a few minutes. The issue is that the human animal wants INSTANT GRATIFICATION and is happy when he can raise the PP02 in a moment. He's unhappy when it takes a few minutes to lower it. He FEARS high PP02 *because he has not been trained that it's a soft limit* and wrongly fears it EQUALLY as much as he fears low PP02. To make it worse, he aparently fears high PP02 MORE SO than low PP02 gas because he carries 10% gas as diluent that will KILL HIM IN MOMENT near the surface to get past his fear of having a gas that "may" do something in about 4 *hours* on the bottom *maybe*. This is where he is WRONG. The only way he can meet his desire for instant gratification is to often dive a mix that will KILL HIM if breathed on it's own at the suface. But he then forgets that he can actually DIVE the same planned loop-gas by starting with a higher PP02 mix to begin with and "on a dive every now and then" end up with a mix that *for a FEW MINUTES* will be "A LITTLE HOT" in return for the safety of having good gas shallower.

Here's a practical example: If I dive 21% mix as diluent at 250 feet, I am on 1.8 *for less than a minute*. I am at 1.7 for *another minute or so*. I am at 1.6 *for another minute* (and did thousands of hours at 1.6 as a commercial diver so I am already within my "infinite time duration comfort zone"). I am on 1.5 *for another minute*. I am at 1.4 *IN ANOTHER MINUTE* and ONLY THEN does my solenoid begin to fire and maintain my setpoint PP02. If you run 1.2 it takes another TWO MINUTES at most before your loop gas is stabilized at setpoint. And this is at 250 feet! Dive shallower and the problem is of shorter duration and at about 180 feet or shallower it goes away. I know we all dream of diving the Britannic, but seriously: What fraction of your diving is done at 70 to 180 feet? My guess is the majority. For ALL of that, 21% dil is the way to go. My Doria mix? 21/50 trimix as offboard diluent, carried in a 40 cubic foot stage (plumbed to a BOV just in case too, I'm not a "pure" Alpinist, after all). 50/50 nitrox, as internal diluent (feeds my suit as it's normal job), and my 02. I have enough diluent to do a SCC bailout with EASE after loosing any one of my gas supplies (including the 02). I can "almost" do OC deco with this gas suppy if I blow off my deep stops.

NOBODY is diving *for any duration at all* at elevated PP02's using the method. It has zip to do with multi day diving or any of the other things you raise. We used to do an hour+ of *in water pure 02 decompression* EVERY DAY as commercial mixed gas divers. I just don't see the issue with a FEW MINUTES above 1.2 (or 1.4 or whatever) in return for having BETTER and SAFER gas available at all times.

Dave

Dave Sutton · 31st December 2006, 00:14

Quote: (Originally Posted by Steve)

. I plan my dil to be 0.1 lower than my planned pO2 for the max depth of the dive. Dud sensor info can be cross checked this way.

This is highly sensible and is something I can endorse.

What I cannot endorse is a guy diving at 150 feet on 10% and not seeing that it is less safe than diving 21%.

Agreed that cells are an issue. I pot-test mine to 2.0 PP02 as a routine check.

Dave

***diverklondike*** · 31st December 2006, 00:28

All very good points on both sides...

90% of the time my dil is 10/52.... Good or bad the reasons are... (in no special order....
1) Easy to mix and top off
2) From 100 ft to 280 or so I use the same dil... simple simple simple
3) It makes the math dam simple for verifying that your cells are working properly based on a dil flush. #of ATM x .1 .... You have to like that..
4) I do like to have a mix that will do a reasonable job of reducing my ppo2 if it's spiking for some reason...

For the reasons that Dave has mentioned my bailout mixes for a 250ft dive typically 20/30 and 40/30. My preference will always be SCR versus full OC bailout...

Personally I am less concerned about not being able to elevate my ppo2 level since I have a redundant 02 source with me at all times...

Here are the only other times that typically use a different dil...
1) Oyster diving... then it's air....
2) Most cave diving... then it's typically 20/30 for dives in the 100ffw range.
3) Stuff deeper than 280.... then it's some flavor of heliair..

Just my 2 cents... Lots of good conversation regardless...

Dive safe...

Mark

**Steve** · 31st December 2006, 00:36

Quote: (Originally Posted by Dave Sutton)

This is highly sensible and is something I can endorse.

What I cannot endorse is a guy diving at 150 feet on 10% and not seeing that it is less safe than diving 21%.

Agreed that cells are an issue. I pot-test mine to 2.0 PP02 as a routine check.

Dave

Agreed

SteveL · 31st December 2006, 00:38

Dave - firstly hows the new toys??? I was at Cols shop last week from what I heard

Back to the thread - I have to say that I agree with your logic - Personally I dive much like you on the 15.5 - but mount 5l and thats it on most dives to about 60m (200ft) - I get hammered for it but I feel you have to put some faith in the loop - the way the 15.x is designed and the shear number of hours on the unit are impressive. I can always turn it off and run semi closed - which will get me a long way off the bottom then go the 5l. On all of these dives I run 21/35 premix - which is breathable at 200ft no problems - and the He is a nice to have -

I agree that if you rip a hose off and have a total and complete unrecoverable flood things will be tricky - BUT if you play the numbers game the chances of this are slim - and on the 15.x possibly slimmer - weakest link is the hoses - so I have changed to the mil spec cooper hoses then wrapped them in a double layer canvas - simple loop protection - KISS

My philosophy is that the loop is golden protect the loop - if you a slowly and quietly moving around in a wreck the chances of tearing the loop are slim in my view - scootering flat out in a cave possible higher -

I think that carrying all that extra crap is just potentially compounding any potential problems - so if you dont need it dont carry it.

Using gas with a high PPO2 all helps to get you out of the water faster. As soon as you start to ascend the PPo2 is heading south at a rapid rate anyway -

I am alway fearful of running hypoxic mixes when you dont have to as it is all to easy to jump in the water with a crap load of tanks on fight a ripping current to the anchor and pass out - sure the adv has kicked in but its not giving you a life sustaining mix - There has been a fatality here in Sydney because of this senario.

It is scary how fast the loop PP02 drops if you climb the rope fast.

Like flying - any landing you can walk away from is a good one - similarly any dive you can climb in the boat from is a good one.

Dive simple dive safe

Steve L

30th December 2006, 23:27	#11 (permalink)
Dave Sutton Membership Cancelled Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Classic Kiss rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,637	Re: ad_ward9 slamming everyone elses gear Quote: (Originally Posted by Doorduijn, Niels) Interesting debate. As a side-comment, for those of you with DAN insurance, and a desire to keep the coverage in place, be aware that under the DAN Europe insurance, the max PpO2 on a technical dive is is 1.4, otherwise the dive is not covered. Rgs, Niels Doorduijn My friend Bill Hamillton, DAN's spiritual founder, would cry if he heard this. You would think that DAN would be happy to have people less likely to get DCS, no? Desk-bound bean counters and shoe-clerks running huge paper feifdoms can go stuff themselves. That's right up with the CE. Thank God I live in the CE-Free good old USA where a man can actually buy the worlds safest rebreather, the KISS .... In any case, carrying hot diluent does NOT mean you are diving a hot mix. Unlike open circuit, you can CARRY 1.6, 1.8, 2.0 as diluent and DIVE 1.4... I do it all the time. Let the lawyers argue about that. They deserve what they get. Tell you what, I'll testify as an expert at any civil trial after they deny coverage. Bet I win too. Dave Sutton Last edited by Dave Sutton : 30th December 2006 at 23:31.
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30th December 2006, 23:37	#12 (permalink)
Steve Ladies bring a plate Current Rebreather/s: Megalodon Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Classic Kiss MK 15.X Home Build Join Date: Feb 2005 Location: Perth - Australia Posts: 1,103	Re: ad_ward9 slamming everyone elses gear Quote: (Originally Posted by EBT) Thats not what I asked though is it dave. The point I was making is that your technique is REQUIRED because you dive alpinist. Someone with OC bailout may choose different techniques since they have an additional tool in the armoury. You have to look at the circumstances to be sure you're being appropriate and avoiding IACDT (as you put it). Personally, my dil at its richest runs to 1.3 PO2, normally its 1.0. My reasons; 1. it provides an effective flush DOWN 2. despite USN limits etc, the world has based their O2 limits on kenneth mcdonalds work and his conlusions were essentially that O2 is unpredictable even within the same individual. I dont want to push that. 3. In an emergency, theres a good chance of elevated adrenaline and a possibility of elevated CO2. Both of those are bad ideas with high O2. one thing we do agree on... hypoxia is serious and immediate, hyperoxia is not quite as serious and definitely not as immediate. I do welcome the alternate views though, it never hurts to understand and consider other approaches. /Z I couldn't agree more Zak. Whilst understanding Dave's point I couldn't disagree with his beliefs on this issue more strenuously if I tried. I just can't get the cold hard fact that every rebreather diver that I knew personally that is no longer with us died from either one or a combination of 4 things; Inadequate bailout volume. They needed more gas. Hyperoxia and then drowning No buddy to help out and fix a small issue that snowballed Skill deficit. They made a simple mistake and they should have known better I feel compelled to learn from their deaths. This topic should get it's own thread IMO __________________ WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types.
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30th December 2006, 23:44	#13 (permalink)
Dave Sutton Membership Cancelled Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Classic Kiss rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,637	Re: ad_ward9 slamming everyone elses gear [quote=Steve;86570]IHyperoxia and then drowning Wait a minute: You actually know of a death caused by high PP02 on a rebreather? Do tell us all about it. All of the dead friends of mine that have died on rebreathers (and there are more than I have fingers on one hand) died due to low PP02. I know of a total of zero divers that have toxed on a rebreather and that's including many hundreds hours of seeing guys dive at 40 feet on the LAR-V as well as my own diving the LAR-V as well as running 1.6 as our normal mix as a commercial diver for thousands of hours. Forget the bailout thing, totally divorce it from the diluent selection discussion as the two are not the same. Is there any reason to select surface-hypoxic mixes if they are not required for the depth planned, or any rationale to select mix where the PP02 of the diluent is not at least equal to the desired PP02 at the desired depth? Forget "greater" than the setpoint PP02, use the term "at least" and start writing. Love to hear all about it. Best, Dave Last edited by Dave Sutton : 30th December 2006 at 23:51.
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31st December 2006, 00:00	#14 (permalink)
dive2dive2000 PRISM DIVER & LUVIN IT! Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Feb 2005 Location: Long Island, NY Posts: 788	Re: ad_ward9 slamming everyone elses gear Quote: (Originally Posted by Dave Sutton) I respectfully disagree. Pick a depth: I'll pick 250 feet. Deep enough to be deep but not scary deep: 21% diluent = 1.8 PP02 US Navy LAR-V 02 limits for 1.8 PP02 = essentially infinite duration (IE: 240 minutes, or 4 hours) If I flush my loop with diluent at 250 using that mix it'll be leaned out to 1.4 in about 4 minutes..... (and note that the time base for this "burn off" changes with loop volume, if you purge to CLVmin <Definition: counterlung volume minimum, volume = tidal volume> it'll slide down faster than if you inject more gas into the counterlung) Let's see, that's an hour of time available against each minute of time used... I'll take that bet! Bottom line is that there is utterly no reason to EVER dive a mix leaner that 21% shallower than 250 feet. Let's take it to the boolean logic string: (1): There is no way in hell I'll get hurt with that mix ever as the time spent on that mix at depth is either open circuit in which case I'm blowing thru it fast or closed circuit where I am decreasing the PP02 fraction thru metabolism is FAR shorter than the time it would take to even come close to acute 02 tox time. And by meaning FAR SHORTER I'm talking hours at 250 feet. AND (2): I can use it as a VERY EFFICIENT SCC mix for bailout modes. AND (3): It is FAR BETTER as a basic deco mix either SCC or Open Circuit than a 10% mix. AND (4): The alternatively proposed 10% mix is LETHAL near the surface in SECONDS. AND (5): 10% makes a poor choice for a SCC gas for "on loop" bailout in case ya'll loose your 02 for some reason. AND (6): 10% dil makes a piss poor deco gas open circuit. THUS (7): Thus there is no rationale for using a 10% mix for this dive. None. No how. No way. Zero. Nada. Zippo. END That's not opinion, it's fact.... makes no difference if you carry bailout or not. 10% dil selection for this sort of dive is just plain wrong and I don't care who teaches that it's OK. They are wrong. The only operational issue with this mix is that you need to purge the loop once on descent (or after reaching bottom), assuming that you allowed the loop to go to higher than 0.21 on the surface. I'll take on that workload in return for the advantages. With my Mark-15 it's easy as I jump in with the rig turned off and it's not trying to inject 02 until I turn it on. I don't turn it on until I hit the bottom anyhow. Makes my purge depth irrelevant. If you dive a rig with "auto-on" power, purge after your depth = your depth for setpoint = diluent PP02 at that depth, assuming that you are diving deeper than where PP02 (setpoint) = PP02 (diluent). Educated Opinion: Where the dive training industry has gone wrong is that it has TOTALLY failed to distinguish in training between the HUGE time difference (MANY orders of magnitude) between the time it takes to have a problem due to high PP02 versus low PP02. This is what I teach: (1): Respect high PPO2 and do something about it In good time. (2): FEAR low PP02 'cause it's gonna kill you RIGHT FRIGGIN' NOW. Oxygen is life. Fear the gas that carries little. Dave I am a little confused at your reasoning. I was taught (and in all honesty it does make sense) that a rebreather is nothing more than a mixing station on your back. You sorta have an open circuit best mix mentality. What about your OTU's. Doing multi day diving between 1.4 and 1.8 does have disadvantages too. While we probably will never come close to OTU limits; do say 3 hrs a day from 1.4 to 1.8 and need a chamber ride on the 3rd day there is a good chance they wont admit you. Right wrong or indifferent that is the way it is. There is always the whole picture and not just a small piece of the puzzle when considering a dive plan, and your prior posts suggested that when it came to buddy diving /solo diving cave diving techniques... different circumstances depend on procedure. I feel 10% is a good mix for dives deeper than 150' for a few reasons I can keep a gas at 1 to 1.3, I can easily do a flush and bring down an elevated PPO2, and I can do multi day diving and still keep my OTU's at a manageable level if god forbid I need a chamber ride. And you said it best in another post "Dr. Hamilton is gonna cry when he reads this" More like scream and cuss is a better analogy __________________ Safe Diving, Martin "but what's the fun of getting what you need, instead of what you want?"
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31st December 2006, 00:11	#15 (permalink)
Steve Ladies bring a plate Current Rebreather/s: Megalodon Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Classic Kiss MK 15.X Home Build Join Date: Feb 2005 Location: Perth - Australia Posts: 1,103	Re: Diluent selection and the great alpinist v siege debate Alpinist V's OC bailout discussion successfully parked 'Selecting surface-hypoxic mixes if they are not required for the depth planned' is agreed as well. PP02 of the diluent at least equal to the desired PP02 at the desired depth. This is the bit I don't like. Like you I have a LAR V background and whilst none of my Navy mates died from tox issues. I have seen enough incidents to warrant caution in my recreational diving as my civilian buddies don't look after my back the way a Navy dive team member does. Moving away from O2 CCRs, taking the ability to do a cell verification or drop the pO2 away from a diver is an unnecessary risk. Cells are the weakest part of every rebreather out there and I like every tool possible in verifying them. I plan my dil to be 0.1 lower than my planned pO2 for the max depth of the dive. Dud sensor info can be cross checked this way. Also, if the dil has a higher than planned diving pO2 and there is an O2 leak, solenoid jam etc you are forced to breath it down. Fine if one can ascend granted but a bit too much pucker factor if it isn't a option for a while Fred Evans fitted and drowned. His sensors were current limited so his pO2 was higher than he believed it to be. __________________ WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types. Last edited by Steve : 31st December 2006 at 00:16.
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31st December 2006, 00:11	#16 (permalink)
Dave Sutton Membership Cancelled Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Classic Kiss rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,637	Re: ad_ward9 slamming everyone elses gear Quote: (Originally Posted by dive2dive2000) II feel 10% is a good mix for dives deeper than 150' for a few reasons I can keep a gas at 1 to 1.3, Dude: At 150 feet, 21% mix is 1.1 PP02. That's 0.1 LESS than a sort of normal 1.2 PP02 setpoint. Why in the world would you want your diluent to be LESS THAN HALF of your target setpoint? I mean, heck: Why don't you just dive pure inert gas as your diluent? Your 10% at 150 feet is doing you about as much good. Don't you WANT to be able to breathe that gas at the surface if you can? Yes, a rebreather is a "gas mixing station on your back". What instructors apparently are failing to teach is that not only can you RAISE a low PP02 mix to a good mix by ADDING 02, you can also LOWER a "slightly" rich mix to a good one in a time period that you can ignore for all practical purposes by REMOVING 02. You RAISE PP02 with a push button or a solenoid vave. You REMOVE 02 by BREATHING for a few minutes. The issue is that the human animal wants INSTANT GRATIFICATION and is happy when he can raise the PP02 in a moment. He's unhappy when it takes a few minutes to lower it. He FEARS high PP02 because he has not been trained that it's a soft limit and wrongly fears it EQUALLY as much as he fears low PP02. To make it worse, he aparently fears high PP02 MORE SO than low PP02 gas because he carries 10% gas as diluent that will KILL HIM IN MOMENT near the surface to get past his fear of having a gas that "may" do something in about 4 hours on the bottom maybe. This is where he is WRONG. The only way he can meet his desire for instant gratification is to often dive a mix that will KILL HIM if breathed on it's own at the suface. But he then forgets that he can actually DIVE the same planned loop-gas by starting with a higher PP02 mix to begin with and "on a dive every now and then" end up with a mix that for a FEW MINUTES will be "A LITTLE HOT" in return for the safety of having good gas shallower. Here's a practical example: If I dive 21% mix as diluent at 250 feet, I am on 1.8 for less than a minute. I am at 1.7 for another minute or so. I am at 1.6 for another minute (and did thousands of hours at 1.6 as a commercial diver so I am already within my "infinite time duration comfort zone"). I am on 1.5 for another minute. I am at 1.4 IN ANOTHER MINUTE and ONLY THEN does my solenoid begin to fire and maintain my setpoint PP02. If you run 1.2 it takes another TWO MINUTES at most before your loop gas is stabilized at setpoint. And this is at 250 feet! Dive shallower and the problem is of shorter duration and at about 180 feet or shallower it goes away. I know we all dream of diving the Britannic, but seriously: What fraction of your diving is done at 70 to 180 feet? My guess is the majority. For ALL of that, 21% dil is the way to go. My Doria mix? 21/50 trimix as offboard diluent, carried in a 40 cubic foot stage (plumbed to a BOV just in case too, I'm not a "pure" Alpinist, after all). 50/50 nitrox, as internal diluent (feeds my suit as it's normal job), and my 02. I have enough diluent to do a SCC bailout with EASE after loosing any one of my gas supplies (including the 02). I can "almost" do OC deco with this gas suppy if I blow off my deep stops. NOBODY is diving for any duration at all at elevated PP02's using the method. It has zip to do with multi day diving or any of the other things you raise. We used to do an hour+ of in water pure 02 decompression EVERY DAY as commercial mixed gas divers. I just don't see the issue with a FEW MINUTES above 1.2 (or 1.4 or whatever) in return for having BETTER and SAFER gas available at all times. Dave Last edited by Dave Sutton : 31st December 2006 at 00:53.
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31st December 2006, 00:14	#17 (permalink)
Dave Sutton Membership Cancelled Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Classic Kiss rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,637	Re: Diluent selection and the great alpinist v siege debate Quote: (Originally Posted by Steve) . I plan my dil to be 0.1 lower than my planned pO2 for the max depth of the dive. Dud sensor info can be cross checked this way. This is highly sensible and is something I can endorse. What I cannot endorse is a guy diving at 150 feet on 10% and not seeing that it is less safe than diving 21%. Agreed that cells are an issue. I pot-test mine to 2.0 PP02 as a routine check. Dave
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31st December 2006, 00:28	#18 (permalink)
*diverklondike* Moderator Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Oct 2005 Location: Delaware, USA Posts: 1,563	Re: Diluent selection and the great alpinist v siege debate All very good points on both sides... 90% of the time my dil is 10/52.... Good or bad the reasons are... (in no special order.... 1) Easy to mix and top off 2) From 100 ft to 280 or so I use the same dil... simple simple simple 3) It makes the math dam simple for verifying that your cells are working properly based on a dil flush. #of ATM x .1 .... You have to like that.. 4) I do like to have a mix that will do a reasonable job of reducing my ppo2 if it's spiking for some reason... For the reasons that Dave has mentioned my bailout mixes for a 250ft dive typically 20/30 and 40/30. My preference will always be SCR versus full OC bailout... Personally I am less concerned about not being able to elevate my ppo2 level since I have a redundant 02 source with me at all times... Here are the only other times that typically use a different dil... 1) Oyster diving... then it's air.... 2) Most cave diving... then it's typically 20/30 for dives in the 100ffw range. 3) Stuff deeper than 280.... then it's some flavor of heliair.. Just my 2 cents... Lots of good conversation regardless... Dive safe... Mark
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31st December 2006, 00:36	#19 (permalink)
Steve Ladies bring a plate Current Rebreather/s: Megalodon Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Classic Kiss MK 15.X Home Build Join Date: Feb 2005 Location: Perth - Australia Posts: 1,103	Re: Diluent selection and the great alpinist v siege debate Quote: (Originally Posted by Dave Sutton) This is highly sensible and is something I can endorse. What I cannot endorse is a guy diving at 150 feet on 10% and not seeing that it is less safe than diving 21%. Agreed that cells are an issue. I pot-test mine to 2.0 PP02 as a routine check. Dave Agreed __________________ WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types.
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31st December 2006, 00:38	#20 (permalink)
SteveL Custom Title Allowed! Current Rebreather/s: MK 15.X Other Rebreather/s: Inspiration Classic Join Date: Nov 2005 Location: Sydney Australia Posts: 222	Re: Diluent selection and the great alpinist v siege debate Dave - firstly hows the new toys??? I was at Cols shop last week from what I heard Back to the thread - I have to say that I agree with your logic - Personally I dive much like you on the 15.5 - but mount 5l and thats it on most dives to about 60m (200ft) - I get hammered for it but I feel you have to put some faith in the loop - the way the 15.x is designed and the shear number of hours on the unit are impressive. I can always turn it off and run semi closed - which will get me a long way off the bottom then go the 5l. On all of these dives I run 21/35 premix - which is breathable at 200ft no problems - and the He is a nice to have - I agree that if you rip a hose off and have a total and complete unrecoverable flood things will be tricky - BUT if you play the numbers game the chances of this are slim - and on the 15.x possibly slimmer - weakest link is the hoses - so I have changed to the mil spec cooper hoses then wrapped them in a double layer canvas - simple loop protection - KISS My philosophy is that the loop is golden protect the loop - if you a slowly and quietly moving around in a wreck the chances of tearing the loop are slim in my view - scootering flat out in a cave possible higher - I think that carrying all that extra crap is just potentially compounding any potential problems - so if you dont need it dont carry it. Using gas with a high PPO2 all helps to get you out of the water faster. As soon as you start to ascend the PPo2 is heading south at a rapid rate anyway - I am alway fearful of running hypoxic mixes when you dont have to as it is all to easy to jump in the water with a crap load of tanks on fight a ripping current to the anchor and pass out - sure the adv has kicked in but its not giving you a life sustaining mix - There has been a fatality here in Sydney because of this senario. It is scary how fast the loop PP02 drops if you climb the rope fast. Like flying - any landing you can walk away from is a good one - similarly any dive you can climb in the boat from is a good one. Dive simple dive safe Steve L
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