max PPO2

pimderhoodes · 3rd January 2007, 01:47

Reading the stories about ppo2 from Joe,

In water-pure 02 deco at 40 FSW was observed by me personally for literally *thousands* of hours., right out of the US Navy dive manual and using the tables custom produced for us by Dr. Bill Hamilton..... and we never saw an 02 tox symptom ever. We did *much* longer 40 foot chamber decompressions (hours) after the in-water portion of the deco was done and never saw an issue there either. Every 6 months each diver did a 60 FSW for 30 minute chamber run on pure 02 for the "02 tolerance test" and in literally hundreds of chamber runs we *never* had a hit. Don't take me wrong: 02 tox *is* an issue, just that it's a "fuzzy" limit and not a "hard" one. Go see how the SEALs use LAR-V's for emergency combat escape dives to 75 feet plus (diving in an emergency to below hand-grenade sinking depth) and then talk to me.

makes me ask the question to all of you, how much PPO2 do you use during the dive ?
Are you putting it to the max of 2.0 ? or just doing deco at 2.0.
Or are we all doing the "normal" 1.5 / 1.6

thanks pim

wizbang · 3rd January 2007, 02:01

Hi PIM, I start at 0.7 and move to 1.3 on decent.
I raise the PPO2 to 14. or so from 15m and have it cleared to 1.5 or so from 9m up.

It was easier on the mCCR because there were no anoying alarms above 1.5

Hope that helps.

***ScubaDadMiami*** · 3rd January 2007, 03:02

It all depends on the length of exposure plus factors like how hard I am working. Normally, I stay between 1.0 and 1.2 for the bottom, and then I go with 1.2 or so during ascent and deco. I will also do a flush with O2 at 20 feet if I feel the need (plus it's a good check on the O2 sensors).

Just because some people don't tox at higher limits after surviving a number of exposures without a hit does not mean that this will always be the case. Check out Donald, Oxygen and the Scuba Diver. Anything beyond 1.6 is not very predictable, and individuals can undergo several exposures for long times without hits and then suddenly have a hit within a relatively short exposure the next time.

chunter · 3rd January 2007, 04:01

Picture a gun with 1000 chambers pointed at your head with a single bullet. Wouldn't you prefer to reduce your chances at death if you could? It seems to me that the decompression benefits of raising a PPO2 to 2.0 or even 2.5 are not worth the risks. Clear some stuff off of your schedule if you can't wait the extra 5 minutes.

I regularly do an O2 flush at 20 feet (a 1.6 PPO2) and fly my unit at a 1.3 or 1.4, but I'm not willing to get more aggressive than that. The fact is that divers have died from drowning due to CNS toxicity. Oxygen tolerance is different for everyone and can change in an individual because of CO2 levels, hydration, exertion, the amount of sleep you had the night before, drugs, etc.

Yes, chambers regularly operate at 2.8 PPO2, but it isn't lethal when people tox in the chamber. Even chambers generally use 5 minute air breaks for every 20 minutes on O2. Anyone here taking air breaks during their dives? As far as the military goes, I think that they are willing to accept higher risk for their divers than I am willing to take, especially when I'm diving a rig that gives me the option of using a lower PPO2 (ie, not an oxygen rebreather). I also don't have to weigh my risks of CNS tox against people shooting at me.

There are quite a few people advocating using very high PPO2s, but I can't see the benefit. Take the following dives for example (I'm sorry but I only have my VR3 with me right now to run tables, but you will get the idea):

- 140 feet for 45 minutes using a 1.3 on the bottom and starting O2 at 40 feet (a 2.19). You will have a TTS of 33 minutes with the following stops:
70ft for 1 min
60ft for 2 min
50ft for 2 min
40ft for 3 min
30ft for 5 min
20ft for 7 min
10ft for 11 min

- 140 feet for 45 minutes using a 1.3 for the entire dive. You will have a TTS of 39 minutes with the following stops:
70ft for 1 min
60ft for 2 min
50ft for 3 min
40ft for 5 min
30ft for 6 min
20ft for 9 min
10ft for 11 min

It hardly seems worth the risk to save 6 minutes deco. You would be better to shorten your bottom time by a minute or two.

Now do the same dive using a 1.6 for the entire dive (except at your 10 foot stop). You will have a TTS of 27 minutes with the following stops:
60ft for 1 min
50ft for 1 min
40ft for 2 min
30ft for 4 min
20ft for 7 min
10ft for 9 min
Congratulations, you saved yourself 12 minutes. Now you can get back to work sooner.

I realize that longer and deeper dives create more of a difference, however, they also create more of a risk of a CNS hit. Even on a 3 hour trimix dive, you would only reduce your decompression by about 20% if you were to run a 1.6 instead of a 1.3. Again, shorten your bottom time if you don't want to do the deco.

I guess if I were in a real hurry to shorten deco times, I'd bump up my PPO2, but I'd use a full face mask and I'd try to find a really good dive buddy.

Aloha,
Charlie

Gobfish1 · 3rd January 2007, 09:12

On dives to say 70m
I would run 1,3 bottom
when I get back to say 15m I tend to start to push up the ppo2 max 1.45
Always like to keep my cns clock round 85% or less .
But don’t mind going over 100% if need be
So after a 70m dive I would be back at 6m round 65min run time .55cns per min * 65mins = 36% on my clock and I would have 45mins deco to do a 6m if I push my ppo2 up to 1.6 I will go over my cns clock i.e. 2.2 cns per min * 45mins deco time to do = 99+36=135% on my clock ,
But if I keep my ppo2 at say 1.5 I get .83*45= 37+36=73% on my cns clock
I just keep 3 numbers in my head
1.6 = 2 cns per min
1.4 to 1.5 = 1 cns per min
1.3 set point gives me 6 cns per ten mins of use
That way I can do the numbers in my head and all ways have a good handle on my total CNS clock at all points of my dive .And can change my ppo2 to keep me in side my happy zone ,ps i have a vr3 that will keep track of cns as well ,

but to look 4ward i need my head

So to answer the question . 1.3 on bottom and push my ppo2 up as I think fit , for the dive .
Ps
I have dived with a guy that dos 1.9 ppo2 deco on OC ,
I have seen him do this and he was fine but I will stick with my 1,3 & 1.6 it works for me

I would be happly to breath 1.9 if i had to , put not for to long, me thinks

Mikel-Deko · 3rd January 2007, 10:27

Hi

My 5 cents

In the 0-60 range 1.3 botton, and 1.6 6mtrs

Down 60 mtrs, 1.2 botton, from the 1st deep stop 1.4 and 1.6 for 6 mtrs. Looking close to the CNS clock, and making breaks of 5 minutes in 0.5.

Regards

Mikel HAPPY NEW YEAR

6Gill · 3rd January 2007, 14:27

I believe the USN has abandoned the 60 for 30 O2 tolerance test. We used to do this in the seventies when I was in; and I did have 2 guys (out of about 150 that I tended) tox on the tests while I was a chamber tender. Since I left, I'm told the Navy reached the conclusion that the test really wasn't valid as a person could pass it one day and fail at a future date. PO2 above 2.0 would be an option in combat or with FFM but IMHO probably isn't worth the elevated risk in sport diving.

Quote: (Originally Posted by pimderhoodes)

Reading the stories about ppo2 from Joe,

In water-pure 02 deco at 40 FSW was observed by me personally for literally *thousands* of hours., right out of the US Navy dive manual and using the tables custom produced for us by Dr. Bill Hamilton..... and we never saw an 02 tox symptom ever. We did *much* longer 40 foot chamber decompressions (hours) after the in-water portion of the deco was done and never saw an issue there either. Every 6 months each diver did a 60 FSW for 30 minute chamber run on pure 02 for the "02 tolerance test" and in literally hundreds of chamber runs we *never* had a hit. Don't take me wrong: 02 tox *is* an issue, just that it's a "fuzzy" limit and not a "hard" one. Go see how the SEALs use LAR-V's for emergency combat escape dives to 75 feet plus (diving in an emergency to below hand-grenade sinking depth) and then talk to me.

makes me ask the question to all of you, how much PPO2 do you use during the dive ?
Are you putting it to the max of 2.0 ? or just doing deco at 2.0.
Or are we all doing the "normal" 1.5 / 1.6

thanks pim

pimderhoodes · 3rd January 2007, 17:14

Thanks guys !!

i use the 1.5 most of the time, not really being worried about the 100% cns. Diving with a FFM EXO, i feel happy with that. I just changed from inspiration to the Oros. The inspiration wouldn't allow ppo2 above the 1.5 so i was happy/curious about the max in the Oros.

And Happy New Year, that we all can worry about diving and never about our health.

***Decodiver*** · 3rd January 2007, 18:00

I dive and deco at 1.3 shallower than 100 metres.

Deeper than 100 metres I use 1.0 PPO2 on the bottom with a diluent that gives me that should I need to SCR back to the shot and deco at 1.3 up to 6 metres where I manually maintain 1.4.

I do not believe that oxygen is our friend, I believe it is a fundamental & necessary bedfellow.

Cheers,

Dave Cooper.

3rd January 2007, 01:47	#1 (permalink)
pimderhoodes New Member Current Rebreather/s: Inspiration Classic Ouroboros Other Rebreather/s: Inspiration Classic Join Date: Nov 2006 Location: belgium Posts: 23	max PPO2 Reading the stories about ppo2 from Joe, In water-pure 02 deco at 40 FSW was observed by me personally for literally thousands of hours., right out of the US Navy dive manual and using the tables custom produced for us by Dr. Bill Hamilton..... and we never saw an 02 tox symptom ever. We did much longer 40 foot chamber decompressions (hours) after the in-water portion of the deco was done and never saw an issue there either. Every 6 months each diver did a 60 FSW for 30 minute chamber run on pure 02 for the "02 tolerance test" and in literally hundreds of chamber runs we never had a hit. Don't take me wrong: 02 tox is an issue, just that it's a "fuzzy" limit and not a "hard" one. Go see how the SEALs use LAR-V's for emergency combat escape dives to 75 feet plus (diving in an emergency to below hand-grenade sinking depth) and then talk to me. makes me ask the question to all of you, how much PPO2 do you use during the dive ? Are you putting it to the max of 2.0 ? or just doing deco at 2.0. Or are we all doing the "normal" 1.5 / 1.6 thanks pim
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3rd January 2007, 02:01	#2 (permalink)
wizbang WEB MERMEN Current Rebreather/s: Inspiration Classic Dolphin Home Build Other Rebreather/s: Not Bought Yet Inspiration Vision Evolution Prism Topaz Sport Kiss Classic Kiss Dolphin Home Build Join Date: Feb 2005 Location: Perth Australia Posts: 379	Re: max PPO2 Hi PIM, I start at 0.7 and move to 1.3 on decent. I raise the PPO2 to 14. or so from 15m and have it cleared to 1.5 or so from 9m up. It was easier on the mCCR because there were no anoying alarms above 1.5 Hope that helps.
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3rd January 2007, 03:02	#3 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 1,989	Re: max PPO2 It all depends on the length of exposure plus factors like how hard I am working. Normally, I stay between 1.0 and 1.2 for the bottom, and then I go with 1.2 or so during ascent and deco. I will also do a flush with O2 at 20 feet if I feel the need (plus it's a good check on the O2 sensors). Just because some people don't tox at higher limits after surviving a number of exposures without a hit does not mean that this will always be the case. Check out Donald, Oxygen and the Scuba Diver. Anything beyond 1.6 is not very predictable, and individuals can undergo several exposures for long times without hits and then suddenly have a hit within a relatively short exposure the next time. __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com Last edited by ScubaDadMiami : 3rd January 2007 at 03:06.
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3rd January 2007, 04:01	#4 (permalink)
chunter I like diving Current Rebreather/s: Sport Kiss MK 15.X Other Rebreather/s: Inspiration Classic Inspiration Vision Evolution Classic Kiss Join Date: Jul 2006 Location: Honolulu Posts: 463	Re: max PPO2 Picture a gun with 1000 chambers pointed at your head with a single bullet. Wouldn't you prefer to reduce your chances at death if you could? It seems to me that the decompression benefits of raising a PPO2 to 2.0 or even 2.5 are not worth the risks. Clear some stuff off of your schedule if you can't wait the extra 5 minutes. I regularly do an O2 flush at 20 feet (a 1.6 PPO2) and fly my unit at a 1.3 or 1.4, but I'm not willing to get more aggressive than that. The fact is that divers have died from drowning due to CNS toxicity. Oxygen tolerance is different for everyone and can change in an individual because of CO2 levels, hydration, exertion, the amount of sleep you had the night before, drugs, etc. Yes, chambers regularly operate at 2.8 PPO2, but it isn't lethal when people tox in the chamber. Even chambers generally use 5 minute air breaks for every 20 minutes on O2. Anyone here taking air breaks during their dives? As far as the military goes, I think that they are willing to accept higher risk for their divers than I am willing to take, especially when I'm diving a rig that gives me the option of using a lower PPO2 (ie, not an oxygen rebreather). I also don't have to weigh my risks of CNS tox against people shooting at me. There are quite a few people advocating using very high PPO2s, but I can't see the benefit. Take the following dives for example (I'm sorry but I only have my VR3 with me right now to run tables, but you will get the idea): - 140 feet for 45 minutes using a 1.3 on the bottom and starting O2 at 40 feet (a 2.19). You will have a TTS of 33 minutes with the following stops: 70ft for 1 min 60ft for 2 min 50ft for 2 min 40ft for 3 min 30ft for 5 min 20ft for 7 min 10ft for 11 min - 140 feet for 45 minutes using a 1.3 for the entire dive. You will have a TTS of 39 minutes with the following stops: 70ft for 1 min 60ft for 2 min 50ft for 3 min 40ft for 5 min 30ft for 6 min 20ft for 9 min 10ft for 11 min It hardly seems worth the risk to save 6 minutes deco. You would be better to shorten your bottom time by a minute or two. Now do the same dive using a 1.6 for the entire dive (except at your 10 foot stop). You will have a TTS of 27 minutes with the following stops: 60ft for 1 min 50ft for 1 min 40ft for 2 min 30ft for 4 min 20ft for 7 min 10ft for 9 min Congratulations, you saved yourself 12 minutes. Now you can get back to work sooner. I realize that longer and deeper dives create more of a difference, however, they also create more of a risk of a CNS hit. Even on a 3 hour trimix dive, you would only reduce your decompression by about 20% if you were to run a 1.6 instead of a 1.3. Again, shorten your bottom time if you don't want to do the deco. I guess if I were in a real hurry to shorten deco times, I'd bump up my PPO2, but I'd use a full face mask and I'd try to find a really good dive buddy. Aloha, Charlie
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3rd January 2007, 09:12	#5 (permalink)
Gobfish1 Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Inspiration Classic Inspiration Vision Evolution Join Date: Apr 2005 Location: Manchester UK Posts: 353	Re: max PPO2 On dives to say 70m I would run 1,3 bottom when I get back to say 15m I tend to start to push up the ppo2 max 1.45 Always like to keep my cns clock round 85% or less . But don’t mind going over 100% if need be So after a 70m dive I would be back at 6m round 65min run time .55cns per min * 65mins = 36% on my clock and I would have 45mins deco to do a 6m if I push my ppo2 up to 1.6 I will go over my cns clock i.e. 2.2 cns per min * 45mins deco time to do = 99+36=135% on my clock , But if I keep my ppo2 at say 1.5 I get .8345= 37+36=73% on my cns clock I just keep 3 numbers in my head 1.6 = 2 cns per min 1.4 to 1.5 = 1 cns per min 1.3 set point gives me 6 cns per ten mins of use That way I can do the numbers in my head and all ways have a good handle on my total CNS clock at all points of my dive .And can change my ppo2 to keep me in side my happy zone ,ps i have a vr3 that will keep track of cns as well , but to look 4ward i need my head So to answer the question . 1.3 on bottom and push my ppo2 up as I think fit , for the dive . Ps I have dived with a guy that dos 1.9 ppo2 deco on OC , I have seen him do this and he was fine but I will stick with my 1,3 & 1.6 it works for me I would be happly to breath 1.9 if i had to , put not for to long, me thinks __________________ Steve G Apparently not the only gay diver in the village http://drinkingliberally.org/blogs/o...nzee-glock.gif http://www.scubatunes.com/audio/vol01/mp3/HiTech.mp3 Last edited by Gobfish1 : 3rd January 2007 at 09:20.*
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3rd January 2007, 10:27	#6 (permalink)
Mikel-Deko Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Other CCR Join Date: Jul 2005 Location: Basque Country -Sp- Posts: 417	Re: max PPO2 Hi My 5 cents In the 0-60 range 1.3 botton, and 1.6 6mtrs Down 60 mtrs, 1.2 botton, from the 1st deep stop 1.4 and 1.6 for 6 mtrs. Looking close to the CNS clock, and making breaks of 5 minutes in 0.5. Regards Mikel HAPPY NEW YEAR
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3rd January 2007, 14:27	#7 (permalink)
6Gill Custom Title Allowed! Current Rebreather/s: Megalodon Classic Kiss Other Rebreather/s: Join Date: Apr 2006 Location: Washington state Posts: 115	Re: max PPO2 I believe the USN has abandoned the 60 for 30 O2 tolerance test. We used to do this in the seventies when I was in; and I did have 2 guys (out of about 150 that I tended) tox on the tests while I was a chamber tender. Since I left, I'm told the Navy reached the conclusion that the test really wasn't valid as a person could pass it one day and fail at a future date. PO2 above 2.0 would be an option in combat or with FFM but IMHO probably isn't worth the elevated risk in sport diving. Quote: (Originally Posted by pimderhoodes) Reading the stories about ppo2 from Joe, In water-pure 02 deco at 40 FSW was observed by me personally for literally thousands of hours., right out of the US Navy dive manual and using the tables custom produced for us by Dr. Bill Hamilton..... and we never saw an 02 tox symptom ever. We did much longer 40 foot chamber decompressions (hours) after the in-water portion of the deco was done and never saw an issue there either. Every 6 months each diver did a 60 FSW for 30 minute chamber run on pure 02 for the "02 tolerance test" and in literally hundreds of chamber runs we never had a hit. Don't take me wrong: 02 tox is an issue, just that it's a "fuzzy" limit and not a "hard" one. Go see how the SEALs use LAR-V's for emergency combat escape dives to 75 feet plus (diving in an emergency to below hand-grenade sinking depth) and then talk to me. makes me ask the question to all of you, how much PPO2 do you use during the dive ? Are you putting it to the max of 2.0 ? or just doing deco at 2.0. Or are we all doing the "normal" 1.5 / 1.6 thanks pim __________________ "It's a shame ignorance isn't painful!"
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3rd January 2007, 17:14	#8 (permalink)
pimderhoodes New Member Current Rebreather/s: Inspiration Classic Ouroboros Other Rebreather/s: Inspiration Classic Join Date: Nov 2006 Location: belgium Posts: 23	Re: max PPO2 Thanks guys !! i use the 1.5 most of the time, not really being worried about the 100% cns. Diving with a FFM EXO, i feel happy with that. I just changed from inspiration to the Oros. The inspiration wouldn't allow ppo2 above the 1.5 so i was happy/curious about the max in the Oros. And Happy New Year, that we all can worry about diving and never about our health.
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3rd January 2007, 18:00	#9 (permalink)
*Decodiver* Administrator Current Rebreather/s: Megalodon Ouroboros rEvo Other CCR Other Rebreather/s: Inspiration Classic Inspiration Vision Evolution Sport Kiss Classic Kiss rEvo Other CCR Join Date: Jan 2005 Location: Geneva Posts: 2,172	Re: max PPO2 I dive and deco at 1.3 shallower than 100 metres. Deeper than 100 metres I use 1.0 PPO2 on the bottom with a diluent that gives me that should I need to SCR back to the shot and deco at 1.3 up to 6 metres where I manually maintain 1.4. I do not believe that oxygen is our friend, I believe it is a fundamental & necessary bedfellow. Cheers, Dave Cooper. __________________ CCR/OC Trimix Instructor Trainer CCR Training to Mixed Gas in Switzerland, France, UK & Germany on Megalodon/COPIS-Megalodon/KISS/Sport KISS/Ouroboros/rEvo/Inspiration/Evolution/Sentinel www.zerogravitydiving.com Rebreather World Terms & Conditions
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