Clean Deco

***schford*** · 24th April 2005, 19:00

I had an interesting discussion with AM a few weeks ago around around clean deco.

Which was really focussed around the best way to ensure that your deco profile was clean.

I mean we all plan our decos so that at 6m we are either breathing 1.6 ppo2 which is 100% O2 or some where between 1.3 and 1.4 PPo2 which is pretty darn close.

We also all know that we absorb inert gases into our tissues when we dive and off gas them when we undertake deco through our respiratory system.

But do we conveniantly forget about that when we are under taking deco on our Rebreathers? So that when we think we are breathing our 100% O2 at 6m to minimise our deco time we are actually breathing a fairly large chunk of He / N2 that we have off gassed from our tissues.

AM doesn't and makes sure she cleans the loop perodically. You guys all know the drill emtpy loop through nose, refill with O2 repeat 5 times...ensuring she is breathing what she wants to breath not a loop full of off gassed He.

Just wondered what you guys think of it and when you undertake this, obviously the deeper and gnarlier the dives the more important it becomes.

Stuart

***Decodiver*** · 24th April 2005, 19:21

This argument has been around for quite sometime.

Firstly, breathing 100% O2 on a rebreather decostop is a very good way of getting yourself killed, at least one of the fatalities on the Inspiration is thought to have been from elevated PPO2 on stops. The drill you describe would be suitable for O2 CCR.

1.3PPO2 at 6 metres gives an FO2 of 81.25%.

1.4PPO2 at 6 metres gives an FO2 of 87.5%.

You will not be that adversely affected IMHO by the remaining 18.75% and 12.5% of Nitrogen or Helium.

If your unit electronics fail and you are running O2 CCR then I respectfully suggest you need to be taking regular air breaks every 20 minutes or so.

As for the flushes you describe, I have not used them, the only flushes you will find me doing are diluent flushes on dil switch.

Oxygen is not our friend.

***jradomski*** · 24th April 2005, 19:21

Quote: (Originally Posted by schford)

I had an interesting discussion with AM a few weeks ago around around clean deco.

Which was really focussed around the best way to ensure that your deco profile was clean.

I mean we all plan our decos so that at 6m we are either breathing 1.6 ppo2 which is 100% O2 or some where between 1.3 and 1.4 PPo2 which is pretty darn close.

We also all know that we absorb inert gases into our tissues when we dive and off gas them when we undertake deco through our respiratory system.

But do we conveniantly forget about that when we are under taking deco on our Rebreathers? So that when we think we are breathing our 100% O2 at 6m to minimise our deco time we are actually bre3athing a fiarly large chunk of He / N2 still.

AM doesn't and makes sure she cleans the loop perodically. You guys all know the drill emtpy loop through nose, refill with O2 repeat 5 times...ensuring she is breathing what she wants to breath not a loop full of off gasses He.

Just wondered what you guys think of it and when you undertake this, obviously the deeper and gnarlier the dives the more important it becomes.

Stuart

Flushing the loop periodically is part of my training classes.. We plan the dives with the 6m stop using a 1.3po2 and the 3m stop (if there is one) using a 1.0.

We keep the PO2 above the calculated schedule.. At the start of a new stop leg you generally have to flush about 5 minutes in, but as the deco progresses your off-gassing is slowing down and the flushes can be spread out a bit..

When diving the unit as an "oxygen" rebreather after being at depth its not really a true oxygen Rebreather since you have inert gas building up,, You hit 1.6 only immediately after a flush.. If you just add oxygen based on the loop volume dropping you will eventually go hypoxic (assuming the electronics failed)

Using a periodic flush its quite simple keeping the po2 in the 1.4 to 1.5 range, and since you flushed there is very little inert gas so the damn solenoid is not constantly firing and your buoyancy is very stable.

On all but the longest dives there really isn;t a need to take "air" breaks since the po2 is at 1.6 only for short bursts, and most of the time its a more normal po2.

AM · 24th April 2005, 19:44

Sorry Dave but I *totally* disagree here - the military have been using 2.0 bar PPO2 on deco from 10m to shallows for dives done over decades without adverse effects.

*Disclaimer* - I am not advocating that anyone completes decompression at PPO2 elevated beyond 1.6, in fact training agencies recommend less.

Rebreathing helium and other inert components after extremely deep, extended dives is an easy way to get bent. Nitrogen is an EVIL gas to rebreathe (hence the military using HELIOX)- and you will never properly be breathing 1.6 on deco at 6m UNLESS you are periodically flushing out the rebreathed gas from the lungs. In fact you will never be breathing 1.3 (if that's your deco strategy) unless you keep flushing the lungs - you can hear the pattern of the solenoid (on eCCR) reflecting how much inert gas you are breathing back into the loop. Without flushing, you are then rebreathing the inert gas. Hardly good for clean deco. My strategy is QUALITY not QUANTITY.

I have had my CNS past 200% - ZERO air breaks and no ill effects. In fact, I have NEVER taken an air break on ANY dive. I do not accept that suddenly introducing N2 into the deco gas is necessary or beneficial.

I agree that high PPO2 is not good at depth - for example dives to 60,70, 80m+ I sometimes drop my PPO2 for the working (or bottom) part of the dive to 1.0 bar then whack it up high on decompression. (6m stop) - For obvious reasons I won't advocate whacking it up any earlier, the dive police, the convention, the status quo, the party line etc etc.

I don't have time right now to get in depth to the scientifics but research backs up what I am saying - TDI and the other bog standard civilian diving courses do not have access to the same type of data as certain Government bodies.

Regards

AnneMarie

***Decodiver*** · 24th April 2005, 19:51

Quote: (Originally Posted by AnneMarie)

Sorry Dave but I *totally* disagree here - the military have been using 2.0 bar PPO2 on deco from 10m to shallows for dives done over decades without adverse effects.

Rebreathing helium and other inert components after extremely deep, extended dives is an easy way to get bent. Nitrogen is an EVIL gas to rebreathe (hence the military using HELIOX)- and you will never properly be breathing 1.6 on deco at 6m UNLESS you are periodically flushing out the rebreathed gas from the lungs. In fact you will never be breathing 1.3 (if that's your deco strategy) unless you keep flushing the lungs - you can hear the pattern of the solenoid (on eCCR) reflecting how much inert gas you are breathing back into the loop. Without flushing, you are then rebreathing the inert gas. Hardly good for clean deco. My strategy is QUALITY not QUANTITY.

I have had my CNS past 200% - ZERO air breaks and no ill effects.

I agree that high PPO2 is not good at depth - for example dives to 60,70, 80m+ I sometimes drop my PPO2 for the working (or bottom) part of the dive to 1.0 bar then whack it up high on decompression. (6m stop) - For obvious reasons I won't advocate whacking it up any earlier, the law, the convention, the status quo, the party line etc etc.

I don't have time right now to get in depth to the scientifics but research backs up what I am saying - TDI and the other bog standard civilian diving courses do not.

Regards

AnneMarie

AnneMarie,

As an ex-military diver myself I am aware of diving practices used by a number of military outfits.

It was acceptable in my time on pure O2 CCR to have 45 second windows to go to 40 metres, guess they were trying to kill me.

In WW2 Italian combat divers used O2 to 20 metres.

As for the statement that no adverse effects have occurred I disagree, there are a number of dead military CCR divers to attest to that fact.

There is however a massive difference between military and sports diving.

I do not disagree with the other parts of your reply, yes I agree that the inert gases are present and you can remove them with flushes, I am simply saying that I do not personally travel that close to the line to bother.

Cheers,

Dave

AM · 24th April 2005, 19:54

Quote: (Originally Posted by Decodiver)

AnneMarie,

As an ex-military diver myself I am aware of diving practices used by a number of military outfits.

It was acceptable in my time on pure O2 CCR to have 45 second windows to go to 40 metres, guess they were trying to kill me.

In WW2 Italian combat divers used O2 to 20 metres.

There is however a massive difference between military and sports diving.

I do not disagree with the other parts of your reply, yes I agree that the inert gases are present and you can remove them with flushes, I am simply saying that I do not personally travel that close to the line to bother.

Cheers,

Dave

See? And you're still alive Dave!

But we are agreed I think that on more extreme profiles different deco strategies have to be deployed (I'm not talking going down a line and coming back up, i.e. the average square profile)

Regards

AnneMarie

***schford*** · 24th April 2005, 19:55

Quote: (Originally Posted by jradomski)

Flushing the loop periodically is part of my training classes.. We plan the dives with the 6m stop using a 1.3po2 and the 3m stop (if there is one) using a 1.0.

We keep the PO2 above the calculated schedule.. At the start of a new stop leg you generally have to flush about 5 minutes in, but as the deco progresses your off-gassing is slowing down and the flushes can be spread out a bit..

Sounds like a great course you run Joe. Is this part of the standard course content or are the students benefiting from your experience.

Stuart

***schford*** · 24th April 2005, 20:00

NOAA teach that a PPo2 of 2 for 30 mins in exceptional circumstances is ok...

***Decodiver*** · 24th April 2005, 20:03

Quote: (Originally Posted by AnneMarie)

See? And you're still alive Dave!

But we are agreed I think that on more extreme profiles different deco strategies have to be deployed (I'm not talking going down a line and coming back up, i.e. the average square profile)

Regards

AnneMarie

For day-in day-out repetitive diving, clean deco is more of an issue, I do not run that close to the line, I also take days off on expeditions, normally to sort some or other logistical nightmare out.

Take air breaks to be a generic term.

***caveseeker7*** · 24th April 2005, 20:23

I'm not trimix trained, so my knowledge of the subject is very limited.

But as far as Stuart's question is concerned, I tend to site with AnneMarie and Joe.
Why keep inhaling the gas you just got rid of, getting rid of it seems to be the entire purpose of deco stops. For procedure Joe's approach seems to make a lot of sense.

As for hyperoxic Inspiration accidents, what was the actual loop pO2?
Having seen VR3 printouts of one unit comparing the stock electronics with the HH on 70m dives, the stock electronics seem to have problems keeping the setpoint.
The dive was at 1.3 ata, deco set to 1.5 ata, later 1.6 ata, and the VR3 read 1.8 ata for much of it, getting close to hit 1.9 ata (the HH, btw, did a lot better).

As for diving with excessive pO2, I just recently watched Hans Hass' "Adventures in The Red Sea" from 1952. They were all diving Dräger O2 units, proudly to 25m! And yes, they were actually filmed flushing the loop on the way in, and pulling an unconcious Lotte out of wreck ... . When I saw her a few years ago in Santa Barbara for the UW Film Festival she kept complaining about being unable to ski the previous winter due to a hip replacement surgery while having to drop her hubby off at the slopes.

24th April 2005, 19:00	#1 (permalink)
*schford* Despotic Overlord Current Rebreather/s: Megalodon Sport Kiss Other Rebreather/s: Join Date: Jan 2005 Location: London, UK Posts: 3,671	Clean Deco I had an interesting discussion with AM a few weeks ago around around clean deco. Which was really focussed around the best way to ensure that your deco profile was clean. I mean we all plan our decos so that at 6m we are either breathing 1.6 ppo2 which is 100% O2 or some where between 1.3 and 1.4 PPo2 which is pretty darn close. We also all know that we absorb inert gases into our tissues when we dive and off gas them when we undertake deco through our respiratory system. But do we conveniantly forget about that when we are under taking deco on our Rebreathers? So that when we think we are breathing our 100% O2 at 6m to minimise our deco time we are actually breathing a fairly large chunk of He / N2 that we have off gassed from our tissues. AM doesn't and makes sure she cleans the loop perodically. You guys all know the drill emtpy loop through nose, refill with O2 repeat 5 times...ensuring she is breathing what she wants to breath not a loop full of off gassed He. Just wondered what you guys think of it and when you undertake this, obviously the deeper and gnarlier the dives the more important it becomes. Stuart
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24th April 2005, 19:21	#2 (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: 2,178	This argument has been around for quite sometime. Firstly, breathing 100% O2 on a rebreather decostop is a very good way of getting yourself killed, at least one of the fatalities on the Inspiration is thought to have been from elevated PPO2 on stops. The drill you describe would be suitable for O2 CCR. 1.3PPO2 at 6 metres gives an FO2 of 81.25%. 1.4PPO2 at 6 metres gives an FO2 of 87.5%. You will not be that adversely affected IMHO by the remaining 18.75% and 12.5% of Nitrogen or Helium. If your unit electronics fail and you are running O2 CCR then I respectfully suggest you need to be taking regular air breaks every 20 minutes or so. As for the flushes you describe, I have not used them, the only flushes you will find me doing are diluent flushes on dil switch. Oxygen is not our friend. __________________ 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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24th April 2005, 19:21	#3 (permalink)
*jradomski* Moderator Current Rebreather/s: Inspiration Classic Sport Kiss Optima rEvo Other CCR Home Build Other Rebreather/s: Inspiration Vision Evolution Megalodon Classic Kiss rEvo Other CCR Home Build Join Date: Mar 2005 Location: "Da" Bronx Posts: 2,871	Quote: (Originally Posted by schford) I had an interesting discussion with AM a few weeks ago around around clean deco. Which was really focussed around the best way to ensure that your deco profile was clean. I mean we all plan our decos so that at 6m we are either breathing 1.6 ppo2 which is 100% O2 or some where between 1.3 and 1.4 PPo2 which is pretty darn close. We also all know that we absorb inert gases into our tissues when we dive and off gas them when we undertake deco through our respiratory system. But do we conveniantly forget about that when we are under taking deco on our Rebreathers? So that when we think we are breathing our 100% O2 at 6m to minimise our deco time we are actually bre3athing a fiarly large chunk of He / N2 still. AM doesn't and makes sure she cleans the loop perodically. You guys all know the drill emtpy loop through nose, refill with O2 repeat 5 times...ensuring she is breathing what she wants to breath not a loop full of off gasses He. Just wondered what you guys think of it and when you undertake this, obviously the deeper and gnarlier the dives the more important it becomes. Stuart Flushing the loop periodically is part of my training classes.. We plan the dives with the 6m stop using a 1.3po2 and the 3m stop (if there is one) using a 1.0. We keep the PO2 above the calculated schedule.. At the start of a new stop leg you generally have to flush about 5 minutes in, but as the deco progresses your off-gassing is slowing down and the flushes can be spread out a bit.. When diving the unit as an "oxygen" rebreather after being at depth its not really a true oxygen Rebreather since you have inert gas building up,, You hit 1.6 only immediately after a flush.. If you just add oxygen based on the loop volume dropping you will eventually go hypoxic (assuming the electronics failed) Using a periodic flush its quite simple keeping the po2 in the 1.4 to 1.5 range, and since you flushed there is very little inert gas so the damn solenoid is not constantly firing and your buoyancy is very stable. On all but the longest dives there really isn;t a need to take "air" breaks since the po2 is at 1.6 only for short bursts, and most of the time its a more normal po2. __________________ Joe Radomski CCR Trimix Instructor Trainer ANDI Instructor Trainer Director #10 All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.
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24th April 2005, 19:44	#4 (permalink)
AM Highly amused!! Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Earth. Posts: 554	Sorry Dave but I totally disagree here - the military have been using 2.0 bar PPO2 on deco from 10m to shallows for dives done over decades without adverse effects. Disclaimer - I am not advocating that anyone completes decompression at PPO2 elevated beyond 1.6, in fact training agencies recommend less. Rebreathing helium and other inert components after extremely deep, extended dives is an easy way to get bent. Nitrogen is an EVIL gas to rebreathe (hence the military using HELIOX)- and you will never properly be breathing 1.6 on deco at 6m UNLESS you are periodically flushing out the rebreathed gas from the lungs. In fact you will never be breathing 1.3 (if that's your deco strategy) unless you keep flushing the lungs - you can hear the pattern of the solenoid (on eCCR) reflecting how much inert gas you are breathing back into the loop. Without flushing, you are then rebreathing the inert gas. Hardly good for clean deco. My strategy is QUALITY not QUANTITY. I have had my CNS past 200% - ZERO air breaks and no ill effects. In fact, I have NEVER taken an air break on ANY dive. I do not accept that suddenly introducing N2 into the deco gas is necessary or beneficial. I agree that high PPO2 is not good at depth - for example dives to 60,70, 80m+ I sometimes drop my PPO2 for the working (or bottom) part of the dive to 1.0 bar then whack it up high on decompression. (6m stop) - For obvious reasons I won't advocate whacking it up any earlier, the dive police, the convention, the status quo, the party line etc etc. I don't have time right now to get in depth to the scientifics but research backs up what I am saying - TDI and the other bog standard civilian diving courses do not have access to the same type of data as certain Government bodies. Regards AnneMarie __________________ Attitude keeps you alive
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24th April 2005, 19:51	#5 (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: 2,178	Quote: (Originally Posted by AnneMarie) Sorry Dave but I totally disagree here - the military have been using 2.0 bar PPO2 on deco from 10m to shallows for dives done over decades without adverse effects. Rebreathing helium and other inert components after extremely deep, extended dives is an easy way to get bent. Nitrogen is an EVIL gas to rebreathe (hence the military using HELIOX)- and you will never properly be breathing 1.6 on deco at 6m UNLESS you are periodically flushing out the rebreathed gas from the lungs. In fact you will never be breathing 1.3 (if that's your deco strategy) unless you keep flushing the lungs - you can hear the pattern of the solenoid (on eCCR) reflecting how much inert gas you are breathing back into the loop. Without flushing, you are then rebreathing the inert gas. Hardly good for clean deco. My strategy is QUALITY not QUANTITY. I have had my CNS past 200% - ZERO air breaks and no ill effects. I agree that high PPO2 is not good at depth - for example dives to 60,70, 80m+ I sometimes drop my PPO2 for the working (or bottom) part of the dive to 1.0 bar then whack it up high on decompression. (6m stop) - For obvious reasons I won't advocate whacking it up any earlier, the law, the convention, the status quo, the party line etc etc. I don't have time right now to get in depth to the scientifics but research backs up what I am saying - TDI and the other bog standard civilian diving courses do not. Regards AnneMarie AnneMarie, As an ex-military diver myself I am aware of diving practices used by a number of military outfits. It was acceptable in my time on pure O2 CCR to have 45 second windows to go to 40 metres, guess they were trying to kill me. In WW2 Italian combat divers used O2 to 20 metres. As for the statement that no adverse effects have occurred I disagree, there are a number of dead military CCR divers to attest to that fact. There is however a massive difference between military and sports diving. I do not disagree with the other parts of your reply, yes I agree that the inert gases are present and you can remove them with flushes, I am simply saying that I do not personally travel that close to the line to bother. Cheers, Dave __________________ 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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24th April 2005, 19:54	#6 (permalink)
AM Highly amused!! Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Earth. Posts: 554	Quote: (Originally Posted by Decodiver) AnneMarie, As an ex-military diver myself I am aware of diving practices used by a number of military outfits. It was acceptable in my time on pure O2 CCR to have 45 second windows to go to 40 metres, guess they were trying to kill me. In WW2 Italian combat divers used O2 to 20 metres. There is however a massive difference between military and sports diving. I do not disagree with the other parts of your reply, yes I agree that the inert gases are present and you can remove them with flushes, I am simply saying that I do not personally travel that close to the line to bother. Cheers, Dave See? And you're still alive Dave! But we are agreed I think that on more extreme profiles different deco strategies have to be deployed (I'm not talking going down a line and coming back up, i.e. the average square profile) Regards AnneMarie __________________ Attitude keeps you alive
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24th April 2005, 19:55	#7 (permalink)
*schford* Despotic Overlord Current Rebreather/s: Megalodon Sport Kiss Other Rebreather/s: Join Date: Jan 2005 Location: London, UK Posts: 3,671	Quote: (Originally Posted by jradomski) Flushing the loop periodically is part of my training classes.. We plan the dives with the 6m stop using a 1.3po2 and the 3m stop (if there is one) using a 1.0. We keep the PO2 above the calculated schedule.. At the start of a new stop leg you generally have to flush about 5 minutes in, but as the deco progresses your off-gassing is slowing down and the flushes can be spread out a bit.. Sounds like a great course you run Joe. Is this part of the standard course content or are the students benefiting from your experience. Stuart
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24th April 2005, 20:00	#8 (permalink)
*schford* Despotic Overlord Current Rebreather/s: Megalodon Sport Kiss Other Rebreather/s: Join Date: Jan 2005 Location: London, UK Posts: 3,671	NOAA teach that a PPo2 of 2 for 30 mins in exceptional circumstances is ok...
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24th April 2005, 20:03	#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: 2,178	Quote: (Originally Posted by AnneMarie) See? And you're still alive Dave! But we are agreed I think that on more extreme profiles different deco strategies have to be deployed (I'm not talking going down a line and coming back up, i.e. the average square profile) Regards AnneMarie For day-in day-out repetitive diving, clean deco is more of an issue, I do not run that close to the line, I also take days off on expeditions, normally to sort some or other logistical nightmare out. Take air breaks to be a generic term. __________________ 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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24th April 2005, 20:23	#10 (permalink)
*caveseeker7* Who loves ya, baby Current Rebreather/s: Sport Kiss Other Rebreather/s: Prism Topaz Join Date: Jan 2005 Location: Too far from Neverland Posts: 5,419	I'm not trimix trained, so my knowledge of the subject is very limited. But as far as Stuart's question is concerned, I tend to site with AnneMarie and Joe. Why keep inhaling the gas you just got rid of, getting rid of it seems to be the entire purpose of deco stops. For procedure Joe's approach seems to make a lot of sense. As for hyperoxic Inspiration accidents, what was the actual loop pO2? Having seen VR3 printouts of one unit comparing the stock electronics with the HH on 70m dives, the stock electronics seem to have problems keeping the setpoint. The dive was at 1.3 ata, deco set to 1.5 ata, later 1.6 ata, and the VR3 read 1.8 ata for much of it, getting close to hit 1.9 ata (the HH, btw, did a lot better). As for diving with excessive pO2, I just recently watched Hans Hass' "Adventures in The Red Sea" from 1952. They were all diving Dräger O2 units, proudly to 25m! And yes, they were actually filmed flushing the loop on the way in, and pulling an unconcious Lotte out of wreck ... . When I saw her a few years ago in Santa Barbara for the UW Film Festival she kept complaining about being unable to ski the previous winter due to a hip replacement surgery while having to drop her hubby off at the slopes. __________________ Cheers Stefan "Political Correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.'!"
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