Diving Hypoxic Diluent on a Normoxic Dive

decoweenie · 12th September 2006, 09:23

Quote: (Originally Posted by vulcan)

...I accept you may be sensitive because of the recent experience you had with the student on a hypoxic mix

Correction PLEASE!

He was not my student, and he was not anyone's student. He was an untrained (CCR and mix) diver happened to be on the same boat. He was not under my care nor anyone else's.

I am not going into why it is a bad practice to teach normoxic trimix using hypoxic diluent without full explanation of the dangers.

***EBT*** · 12th September 2006, 09:57

Quote: (Originally Posted by vulcan)

* Note to admin*
I'm conscious we've hijacked someone elses thread here, so if this is more appropriate somewhere else, or in a new thread within the training forum I'm happy for it to be moved.

Done

FWIW, I;ve read reports of people with KISS's switching to OC on the DSV for a surface swim and nearly going "white eyeballs". The Hypoxic dil thing isnt a massive risk, unless you're complacent (a bit like crossing a road really!).

It does also remove the option of an effective SCR mode, unless you plug in offboards.

Dutchy · 12th September 2006, 10:15

Quote: (Originally Posted by EBT)

It does also remove the option of an effective SCR mode, unless you plug in offboards.

Why? My guess would be that a mix with fO2=0.1 would still alow SCR mode up to e.g. 10m (assuming 1on3 breaths is fresh) after which you "sort of flush" with O2 and ascend to 6m after which you thouroughly flush and remain on O2.
("sort of" is a deliberate choice of words as getting to 100% O2 is neither important nor desired @ 10m. (Near 2bar ppO2 exposure should be as short as possible and a bit lower is even better.)

Or is the keyword "effective" here?

silent running · 12th September 2006, 10:24

Quote: (Originally Posted by EBT)

Done

FWIW, I;ve read reports of people with KISS's switching to OC on the DSV for a surface swim and nearly going "white eyeballs". The Hypoxic dil thing isnt a massive risk, unless you're complacent (a bit like crossing a road really!).

It does also remove the option of an effective SCR mode, unless you plug in offboards.

Yes, EBT. But given a hypoxic dil dive plan, shouldn't any hypoxic dil diver have at least 1 normoxic mix to plug in? I had my offboard/transit OC bailout normoxic mix plumbed into my dil 1st stage, only 2 valve turns away. I was actually surprised how much/often O2 was injected on ascent during my first hypoxic dil dive, very instructive of the dangers of a fast ascent on hypoxic dil... -Andy

***EBT*** · 12th September 2006, 10:46

Quote: (Originally Posted by silent running)

Yes, EBT. But given a hypoxic dil dive plan, shouldn't any hypoxic dil diver have at least 1 normoxic mix to plug in? I had my offboard/transit OC bailout normoxic mix plumbed into my dil 1st stage, only 2 valve turns away. I was actually surprised how much/often O2 was injected on ascent during my first hypoxic dil dive, very instructive of the dangers of a fast ascent on hypoxic dil... -Andy

Indeed. Interesting comment about the ascent.... I dont see why you're seeing a difference in O2 injection rate though, once you start an ascent your dil is pretty much immaterial.

dave t · 12th September 2006, 10:52

It was my understanding that a normoxic course was intended as a limited depth course (60m) and depth was limited by the amount of 02 allowed in the diluent. After just reading the IANTD standard it seems they are now limiting the depth by the o2 content in the bailout gas!!!! (20%o2)

I dont agree with that but thats what the standards say so I guess 10/50 is an allowable gas.

Tom if you are reading this would you comment please?

Dave

Padowan · 12th September 2006, 11:55

If the standards state that it's the bailout gas FO2 that is the governing factor, then it would stand to reason that if the diluent is available as an OC source (for example through an AutoAir on the Inspo) then this gas should also be within the "bailout gas" constraints.

If the inboard gas is not available OC (excluding Open Loop and SCR here) then a hypoxic FO2 diluent is not so much of a problem.

With Mod2, is the bailout protocol to get onto OC as soon as possible, or to remain on and preserve the integrity of the loop? If the former, then going SCR or Open Loop would not be primary bailout procedure any way so the Dil FO2 is less important....

dave t · 12th September 2006, 12:13

I think it has to be considered that you may have to bail to oc directly (full loop flood) but there are no gudlines in the standards to say that you couldnt bail to you 10/50 dil to begin with and then switch to the 20% bailout at the apropriate depth, this would mean you could in theory go deeper than 60m and still do a full oc bailout!

silent running · 12th September 2006, 19:19

Quote: (Originally Posted by EBT)

Indeed. Interesting comment about the ascent.... I dont see why you're seeing a difference in O2 injection rate though, once you start an ascent your dil is pretty much immaterial.

Yes, but if you are diving with say 8/65 dil as compared with air dil during the shallower part of an ascent-20m to surface portion-you will notice more O2 injections to keep PO2 at say 1.4 than with an air dil for the same shallow part of an ascent.

Padowan · 13th September 2006, 09:02

Quote: (Originally Posted by silent running)

Yes, but if you are diving with say 8/65 dil as compared with air dil during the shallower part of an ascent-20m to surface portion-you will notice more O2 injections to keep PO2 at say 1.4 than with an air dil for the same shallow part of an ascent.

The only reason I see for this is based on the off-gas rate (and volumes of gas absorbed in the tissues) of helium versus nitrogen.

12th September 2006, 09:23	#11 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,488	Re: Gas Cost for MOD2/3 Quote: (Originally Posted by vulcan) ...I accept you may be sensitive because of the recent experience you had with the student on a hypoxic mix Correction PLEASE! He was not my student, and he was not anyone's student. He was an untrained (CCR and mix) diver happened to be on the same boat. He was not under my care nor anyone else's. I am not going into why it is a bad practice to teach normoxic trimix using hypoxic diluent without full explanation of the dangers. __________________ "...after a while you get bored offering advice to a bull that like to keep butting the fence with its head rather than walking through the open gate..." - Rebreather World PM Last edited by decoweenie : 12th September 2006 at 09:30.
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12th September 2006, 09:57	#12 (permalink)
*EBT* Apprentice Luddite Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Feb 2005 Location: UK, Brighton Posts: 2,147	Re: Gas Cost for MOD2/3 Quote: (Originally Posted by vulcan) * Note to admin* I'm conscious we've hijacked someone elses thread here, so if this is more appropriate somewhere else, or in a new thread within the training forum I'm happy for it to be moved. Done FWIW, I;ve read reports of people with KISS's switching to OC on the DSV for a surface swim and nearly going "white eyeballs". The Hypoxic dil thing isnt a massive risk, unless you're complacent (a bit like crossing a road really!). It does also remove the option of an effective SCR mode, unless you plug in offboards. __________________ Eagles May Soar, but weasels don't get sucked into jet engines! RBW Terms of service
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12th September 2006, 10:15	#13 (permalink)
Dutchy Rene Warries Current Rebreather/s: Sport Kiss Other Rebreather/s: Join Date: Apr 2006 Location: Nieuwegein (The Netherlands) Posts: 891	Re: Gas Cost for MOD2/3 Quote: (Originally Posted by EBT) It does also remove the option of an effective SCR mode, unless you plug in offboards. Why? My guess would be that a mix with fO2=0.1 would still alow SCR mode up to e.g. 10m (assuming 1on3 breaths is fresh) after which you "sort of flush" with O2 and ascend to 6m after which you thouroughly flush and remain on O2. ("sort of" is a deliberate choice of words as getting to 100% O2 is neither important nor desired @ 10m. (Near 2bar ppO2 exposure should be as short as possible and a bit lower is even better.) Or is the keyword "effective" here? __________________ = This post is environmentally friendly. It is composed of 100% recycled electrons only. =
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12th September 2006, 10:24	#14 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,879	Re: Gas Cost for MOD2/3 Quote: (Originally Posted by EBT) Done FWIW, I;ve read reports of people with KISS's switching to OC on the DSV for a surface swim and nearly going "white eyeballs". The Hypoxic dil thing isnt a massive risk, unless you're complacent (a bit like crossing a road really!). It does also remove the option of an effective SCR mode, unless you plug in offboards. Yes, EBT. But given a hypoxic dil dive plan, shouldn't any hypoxic dil diver have at least 1 normoxic mix to plug in? I had my offboard/transit OC bailout normoxic mix plumbed into my dil 1st stage, only 2 valve turns away. I was actually surprised how much/often O2 was injected on ascent during my first hypoxic dil dive, very instructive of the dangers of a fast ascent on hypoxic dil... -Andy
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12th September 2006, 10:46	#15 (permalink)
*EBT* Apprentice Luddite Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Feb 2005 Location: UK, Brighton Posts: 2,147	Re: Gas Cost for MOD2/3 Quote: (Originally Posted by silent running) Yes, EBT. But given a hypoxic dil dive plan, shouldn't any hypoxic dil diver have at least 1 normoxic mix to plug in? I had my offboard/transit OC bailout normoxic mix plumbed into my dil 1st stage, only 2 valve turns away. I was actually surprised how much/often O2 was injected on ascent during my first hypoxic dil dive, very instructive of the dangers of a fast ascent on hypoxic dil... -Andy Indeed. Interesting comment about the ascent.... I dont see why you're seeing a difference in O2 injection rate though, once you start an ascent your dil is pretty much immaterial. __________________ Eagles May Soar, but weasels don't get sucked into jet engines! RBW Terms of service
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12th September 2006, 10:52	#16 (permalink)
dave t RBW Member Current Rebreather/s: Inspiration Classic Inspiration Vision Evolution Sport Kiss Classic Kiss Dolphin Ray Azimuth Home Build Other Rebreather/s: Dolphin Ray Azimuth Home Build Join Date: May 2005 Location: UK Posts: 686	Re: Diving Hypoxic Diluent on a Normoxic Dive It was my understanding that a normoxic course was intended as a limited depth course (60m) and depth was limited by the amount of 02 allowed in the diluent. After just reading the IANTD standard it seems they are now limiting the depth by the o2 content in the bailout gas!!!! (20%o2) I dont agree with that but thats what the standards say so I guess 10/50 is an allowable gas. Tom if you are reading this would you comment please? Dave
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12th September 2006, 11:55	#17 (permalink)
Padowan RBW Member Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Feb 2005 Location: Exeter, UK. Posts: 526	Re: Diving Hypoxic Diluent on a Normoxic Dive If the standards state that it's the bailout gas FO2 that is the governing factor, then it would stand to reason that if the diluent is available as an OC source (for example through an AutoAir on the Inspo) then this gas should also be within the "bailout gas" constraints. If the inboard gas is not available OC (excluding Open Loop and SCR here) then a hypoxic FO2 diluent is not so much of a problem. With Mod2, is the bailout protocol to get onto OC as soon as possible, or to remain on and preserve the integrity of the loop? If the former, then going SCR or Open Loop would not be primary bailout procedure any way so the Dil FO2 is less important.... __________________ Padowan The future's bright, the future's Yellow .....for now padowan.net - Latest Video: Scapa Flow Rebreather Diving
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12th September 2006, 12:13	#18 (permalink)
dave t RBW Member Current Rebreather/s: Inspiration Classic Inspiration Vision Evolution Sport Kiss Classic Kiss Dolphin Ray Azimuth Home Build Other Rebreather/s: Dolphin Ray Azimuth Home Build Join Date: May 2005 Location: UK Posts: 686	Re: Diving Hypoxic Diluent on a Normoxic Dive I think it has to be considered that you may have to bail to oc directly (full loop flood) but there are no gudlines in the standards to say that you couldnt bail to you 10/50 dil to begin with and then switch to the 20% bailout at the apropriate depth, this would mean you could in theory go deeper than 60m and still do a full oc bailout!
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12th September 2006, 19:19	#19 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,879	Re: Gas Cost for MOD2/3 Quote: (Originally Posted by EBT) Indeed. Interesting comment about the ascent.... I dont see why you're seeing a difference in O2 injection rate though, once you start an ascent your dil is pretty much immaterial. Yes, but if you are diving with say 8/65 dil as compared with air dil during the shallower part of an ascent-20m to surface portion-you will notice more O2 injections to keep PO2 at say 1.4 than with an air dil for the same shallow part of an ascent.
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13th September 2006, 09:02	#20 (permalink)
Padowan RBW Member Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Feb 2005 Location: Exeter, UK. Posts: 526	Re: Gas Cost for MOD2/3 Quote: (Originally Posted by silent running) Yes, but if you are diving with say 8/65 dil as compared with air dil during the shallower part of an ascent-20m to surface portion-you will notice more O2 injections to keep PO2 at say 1.4 than with an air dil for the same shallow part of an ascent. The only reason I see for this is based on the off-gas rate (and volumes of gas absorbed in the tissues) of helium versus nitrogen. __________________ Padowan The future's bright, the future's Yellow .....for now padowan.net - Latest Video: Scapa Flow Rebreather Diving
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