Clean Deco

dteubner · 24th April 2005, 23:27

Keep in mind that CNS O2 toxicity is not like a fuse or a time bomb (you're OK at 30 mins and fit at 31). It is unpredictable and idiosyncratic. 1.6 is safe(ish) because very very few people will fit. 2.0 is less safe and some people will fit, not that many but some. The time to onset of the fit will vary both between individuals and in the same individual on different days. O2 combat swimming is not the same as recreational diving, a risk that is acceptable in the one is not OK for the other.

Bennett and Elliott has a table (9.4.2) about USN depth/exposure limits which goes:

ATA O2............Minutes
1.6...............240
1.9...............80
2.06..............25
2.2...............15
2.5...............10

These exposures lead to symptoms in about 2% of divers, a level of risk that is unacceptable in recreational/commercial divers IMHO.

The other issue is the absoulte amount of nitrogen and helium that is off gassed. It's really pretty small, 2 or 3 litres at the most. You shouldn't need to flush over and over again to get rid of this amount of gas

Dave T

***jradomski*** · 25th April 2005, 00:44

Quote: (Originally Posted by dteubner)

Keep in mind that CNS O2 toxicity is not like a fuse or a time bomb (you're OK at 30 mins and fit at 31). It is unpredictable and idiosyncratic. 1.6 is safe(ish) because very very few people will fit. 2.0 is less safe and some people will fit, not that many but some. The time to onset of the fit will vary both between individuals and in the same individual on different days. O2 combat swimming is not the same as recreational diving, a risk that is acceptable in the one is not OK for the other.

Bennett and Elliott has a table (9.4.2) about USN depth/exposure limits which goes:

ATA O2............Minutes
1.6...............240
1.9...............80
2.06..............25
2.2...............15
2.5...............10

These exposures lead to symptoms in about 2% of divers, a level of risk that is unacceptable in recreational/commercial divers IMHO.

The other issue is the absoulte amount of nitrogen and helium that is off gassed. It's really pretty small, 2 or 3 litres at the most. You shouldn't need to flush over and over again to get rid of this amount of gas

Dave T

not to sound condescending but obviously you haven't done dives with long decos... The time to next flush (at the same depth) stretches out as the deco progresses.. 5 minutes when first reaching a level is definately in the ball park, the next is probably closer to 10 minutes, and so on..

I cant give exact figures becuase it really depends on your dco profile, those that get you shallow faster tend to need more fllushing since more of the deco is being done shallow..

if you do your 3m stop time at 6m youll see the loop definately becomes very stable.. now compare this to someone who just does their 6mstop stop then progresses to 3m... You need a flush after about 5 minutes as well..

ANother factor is how small a loop volume you use, small additions of inert don't have as great effect on someone diving a big loop as opposed to someone diving a minimum gas loop.. Its all relative.. Dont forget your diulent has an effect also.. He and N2 come out at different rates.. The times are longer for nitrogen only diluent

During Dives for recreational purposes I tend to keep the deocs relatively short (2 hours or less) During my trimix programs the decos run 2-3 hours typically.. On mission oriented stuff, the deco is as long as it need be...

dteubner · 25th April 2005, 21:21

For those who are interested this spreadsheet calculates how much He and N2 (in litres at 1 ATA) are absorbed in a given dive. It's pretty quick and dirty but gives some idea.

http://www.davidteubner.com/images/G...calculator.xls

Dave T

You are all, of course, welcome to do whatever you want with it.

***jradomski*** · 25th April 2005, 21:55

Quote: (Originally Posted by dteubner)

For those who are interested this spreadsheet calculates how much He and N2 (in litres at 1 ATA) are absorbed in a given dive. It's pretty quick and dirty but gives some idea.

http://www.davidteubner.com/images/G...calculator.xls

Dave T

You are all, of course, welcome to do whatever you want with it.

Your spreadsheet is a nice idea, the problem is the HT doesn't give an accurate display of whats going on.. for example a ccr dive to 100m for 20min using 50%he, 13% oxygen, the controlling compartment is compartment 8 (yours is close to 7 which does still have significant loading) compartments 8 + 9 have significant gas loading and are much slower to release so it will have an effect for a longer period of time.. the fast compartments do have a gas load, but they will be taken care of pretty quickly,, even compartment 5 is still less than 30m HT..

The way you see the offgassing into the loop makes sense, early on the fast compartents are causing the po2 drop, once these drop they have less of an effect and the slow compartments take over, since they take longer to ogffgas they have less an effect on the loop.

Different tissues has different capacities to hold various gases...

***EBT*** · 25th April 2005, 22:08

Some of my amateur flushing observations (not of the small aligator variety);

Its hard to flush to 1.6, you're chasing a setpoint thats hard to hit, since your loops corrugations etc will all trap gas.

The first flush will decay pretty rapidly as you offgas on the stop. Thereafter the offgassing of inerts into the loop slows down rapidly as you deco.

Someone once suggested using this to guage your deco. Not as daft as it sounds but obviously not practical, given the vagaries of the chaotic system.

Final obvious comment.... you can run waaay over 100% CNS, but the speed at which you get there seems to be the governing factor.

Oh and ammers... cmon cmon... publish or be damned

***jradomski*** · 25th April 2005, 22:44

Quote: (Originally Posted by wreckweasel)

Some of my amateur flushing observations (not of the small aligator variety);

Its hard to flush to 1.6, you're chasing a setpoint thats hard to hit, since your loops corrugations etc will all trap gas.

The first flush will decay pretty rapidly as you offgas on the stop. Thereafter the offgassing of inerts into the loop slows down rapidly as you deco.

Someone once suggested using this to guage your deco. Not as daft as it sounds but obviously not practical, given the vagaries of the chaotic system.

Final obvious comment.... you can run waaay over 100% CNS, but the speed at which you get there seems to be the governing factor.

Oh and ammers... cmon cmon... publish or be damned

If the unit is properly calibrated with 100% oxygen, 1.6 @ 6m is not an unatainable goal... When I run my deco classes I check my students and they don't pass the class until they are able to hit it or get pretty damn close...
It just takes practice.. The biggest key is to remember it is very important to flush your lungs as well as make sure you push the gas around the loop.. if you do the such in blow out method, you flushes should use LARGER inhales than normal because you have a big deadspace in your body that has to be minimized..

A big cause for someone nothitting thisnumber especially on the inspiration controllers is having the wrong PO2 on the surface.. with a fulloxygen flush it MUST be the analyized o2 percentage of the cylinder * ambient pressure.. Too many people accept the default 1000mb on the inspiration..

***EBT*** · 25th April 2005, 22:52

Diminishing returns Joe..... its uses a lot of O2 to hard flush the loop much above about 1.55.

I dont deny what you're saying, I just dont think that 0.05 is worth blowing through shedloads (its a new SI unit) of O2 for.

***jradomski*** · 25th April 2005, 23:35

Quote: (Originally Posted by wreckweasel)

Diminishing returns Joe..... its uses a lot of O2 to hard flush the loop much above about 1.55.

I dont deny what you're saying, I just dont think that 0.05 is worth blowing through shedloads (its a new SI unit) of O2 for.

I think its a matter of technique.. I can easily get 1.6 (Ob RBS with OTS counterlungs)without using lots of oxygen, (I want my students to be able to get above 1.5 without much effort)...

This is the way that I do it...

1)inhale as much as I can
2) crush the bags,
3)exhale out of loop as much as I can..
4) Hold the o2 manual in
5) take a deep breath exhale out through the nose
6) take several shorter breathes on the loop to push the gas around the loop
7) vent through OPV and nose as needed

This takes alot less gas than 4 or 5 deep inhales/exhales..

WIth the bags crushed it takes very little gas in the loop.. The actual dead space in this way (on an inspiration - will vary on other RBS) is only about 2l of gas times 1.6 atas..

If you don't crush the bags it takes LOTS of gas.. I don't know the flushing technique that you wer taught, but when done correctly (and if you have access to the counterlungs) you really can eliminate the counterlungs, and the only volume you are flushing is your lungs, the dead space in the cannister, dsv and hoses.

The most likely reason I am efficient at flushing it is I have lot of practice.. to get a good calibrate on the HH I must have 100% oxygen in the loop...

But I agree 1.55 is fine.. I am a hardass in traing just because I want them to perfect their technique.

Joe

.

AM · 25th April 2005, 23:41

I see both sides here. In fairness it is easy on the Inspiration to reach 1.6. When you dump gas overboard on Inspiration or ascend, the controller will automatically help you by firing even when you are flushing. It is slightly more difficult on the KISS. The flow rate and manual over ride on the KISS *definitely* have a slower gas injection rate.

You put a KISS and Inspo together on a shelf, take them to .70 and try to raise PPO2 using respective manual injection and Inspo restrictor - you will see the tangible difference.

Regards

AnneMarie

PS 1.6 is a good test to do at 6m always to verify the linearity of the sensors.

***jradomski*** · 26th April 2005, 00:20

Quote: (Originally Posted by AnneMarie)

I see both sides here. In fairness it is easy on the Inspiration to reach 1.6. When you dump gas overboard on Inspiration or ascend, the controller will automatically help you by firing even when you are flushing. It is slightly more difficult on the KISS. The flow rate and manual over ride on the KISS *definitely* have a slower gas injection rate.

You put a KISS and Inspo together on a shelf, take them to .70 and try to raise PPO2 using respective manual injection and Inspo restrictor - you will see the tangible difference.

Regards

AnneMarie

PS 1.6 is a good test to do at 6m always to verify the linearity of the sensors.

I originally didn't realize he was diving a classic KISS.. Definately no way to eliminate the counterlungs....
He stuck sucking the loop like a Hoover....

I would say a 1.55 is pretty damn good in this case...

24th April 2005, 23:27	#21 (permalink)
dteubner Pedant Current Rebreather/s: Sport Kiss Classic Kiss Other Rebreather/s: Join Date: Mar 2005 Location: Adelaide, Australia Posts: 217	Keep in mind that CNS O2 toxicity is not like a fuse or a time bomb (you're OK at 30 mins and fit at 31). It is unpredictable and idiosyncratic. 1.6 is safe(ish) because very very few people will fit. 2.0 is less safe and some people will fit, not that many but some. The time to onset of the fit will vary both between individuals and in the same individual on different days. O2 combat swimming is not the same as recreational diving, a risk that is acceptable in the one is not OK for the other. Bennett and Elliott has a table (9.4.2) about USN depth/exposure limits which goes: ATA O2............Minutes 1.6...............240 1.9...............80 2.06..............25 2.2...............15 2.5...............10 These exposures lead to symptoms in about 2% of divers, a level of risk that is unacceptable in recreational/commercial divers IMHO. The other issue is the absoulte amount of nitrogen and helium that is off gassed. It's really pretty small, 2 or 3 litres at the most. You shouldn't need to flush over and over again to get rid of this amount of gas Dave T
(Online)

25th April 2005, 00:44	#22 (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: 3,001	Quote: (Originally Posted by dteubner) Keep in mind that CNS O2 toxicity is not like a fuse or a time bomb (you're OK at 30 mins and fit at 31). It is unpredictable and idiosyncratic. 1.6 is safe(ish) because very very few people will fit. 2.0 is less safe and some people will fit, not that many but some. The time to onset of the fit will vary both between individuals and in the same individual on different days. O2 combat swimming is not the same as recreational diving, a risk that is acceptable in the one is not OK for the other. Bennett and Elliott has a table (9.4.2) about USN depth/exposure limits which goes: ATA O2............Minutes 1.6...............240 1.9...............80 2.06..............25 2.2...............15 2.5...............10 These exposures lead to symptoms in about 2% of divers, a level of risk that is unacceptable in recreational/commercial divers IMHO. The other issue is the absoulte amount of nitrogen and helium that is off gassed. It's really pretty small, 2 or 3 litres at the most. You shouldn't need to flush over and over again to get rid of this amount of gas Dave T not to sound condescending but obviously you haven't done dives with long decos... The time to next flush (at the same depth) stretches out as the deco progresses.. 5 minutes when first reaching a level is definately in the ball park, the next is probably closer to 10 minutes, and so on.. I cant give exact figures becuase it really depends on your dco profile, those that get you shallow faster tend to need more fllushing since more of the deco is being done shallow.. if you do your 3m stop time at 6m youll see the loop definately becomes very stable.. now compare this to someone who just does their 6mstop stop then progresses to 3m... You need a flush after about 5 minutes as well.. ANother factor is how small a loop volume you use, small additions of inert don't have as great effect on someone diving a big loop as opposed to someone diving a minimum gas loop.. Its all relative.. Dont forget your diulent has an effect also.. He and N2 come out at different rates.. The times are longer for nitrogen only diluent During Dives for recreational purposes I tend to keep the deocs relatively short (2 hours or less) During my trimix programs the decos run 2-3 hours typically.. On mission oriented stuff, the deco is as long as it need be... __________________ 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.
(Online)

25th April 2005, 21:21	#23 (permalink)
dteubner Pedant Current Rebreather/s: Sport Kiss Classic Kiss Other Rebreather/s: Join Date: Mar 2005 Location: Adelaide, Australia Posts: 217	For those who are interested this spreadsheet calculates how much He and N2 (in litres at 1 ATA) are absorbed in a given dive. It's pretty quick and dirty but gives some idea. http://www.davidteubner.com/images/G...calculator.xls Dave T You are all, of course, welcome to do whatever you want with it.
(Online)

25th April 2005, 21:55	#24 (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: 3,001	Quote: (Originally Posted by dteubner) For those who are interested this spreadsheet calculates how much He and N2 (in litres at 1 ATA) are absorbed in a given dive. It's pretty quick and dirty but gives some idea. http://www.davidteubner.com/images/G...calculator.xls Dave T You are all, of course, welcome to do whatever you want with it. Your spreadsheet is a nice idea, the problem is the HT doesn't give an accurate display of whats going on.. for example a ccr dive to 100m for 20min using 50%he, 13% oxygen, the controlling compartment is compartment 8 (yours is close to 7 which does still have significant loading) compartments 8 + 9 have significant gas loading and are much slower to release so it will have an effect for a longer period of time.. the fast compartments do have a gas load, but they will be taken care of pretty quickly,, even compartment 5 is still less than 30m HT.. The way you see the offgassing into the loop makes sense, early on the fast compartents are causing the po2 drop, once these drop they have less of an effect and the slow compartments take over, since they take longer to ogffgas they have less an effect on the loop. Different tissues has different capacities to hold various gases... __________________ 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.
(Online)

25th April 2005, 22:08	#25 (permalink)
*EBT* Apprentice Luddite Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Feb 2005 Location: UK, Brighton Posts: 1,969	Some of my amateur flushing observations (not of the small aligator variety); Its hard to flush to 1.6, you're chasing a setpoint thats hard to hit, since your loops corrugations etc will all trap gas. The first flush will decay pretty rapidly as you offgas on the stop. Thereafter the offgassing of inerts into the loop slows down rapidly as you deco. Someone once suggested using this to guage your deco. Not as daft as it sounds but obviously not practical, given the vagaries of the chaotic system. Final obvious comment.... you can run waaay over 100% CNS, but the speed at which you get there seems to be the governing factor. Oh and ammers... cmon cmon... publish or be damned __________________ Eagles May Soar, but weasels don't get sucked into jet engines! Rebreather World Terms of service Real diving t-shirts for real divers
(Offline)

25th April 2005, 22:44	#26 (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: 3,001	Quote: (Originally Posted by wreckweasel) Some of my amateur flushing observations (not of the small aligator variety); Its hard to flush to 1.6, you're chasing a setpoint thats hard to hit, since your loops corrugations etc will all trap gas. The first flush will decay pretty rapidly as you offgas on the stop. Thereafter the offgassing of inerts into the loop slows down rapidly as you deco. Someone once suggested using this to guage your deco. Not as daft as it sounds but obviously not practical, given the vagaries of the chaotic system. Final obvious comment.... you can run waaay over 100% CNS, but the speed at which you get there seems to be the governing factor. Oh and ammers... cmon cmon... publish or be damned If the unit is properly calibrated with 100% oxygen, 1.6 @ 6m is not an unatainable goal... When I run my deco classes I check my students and they don't pass the class until they are able to hit it or get pretty damn close... It just takes practice.. The biggest key is to remember it is very important to flush your lungs as well as make sure you push the gas around the loop.. if you do the such in blow out method, you flushes should use LARGER inhales than normal because you have a big deadspace in your body that has to be minimized.. A big cause for someone nothitting thisnumber especially on the inspiration controllers is having the wrong PO2 on the surface.. with a fulloxygen flush it MUST be the analyized o2 percentage of the cylinder * ambient pressure.. Too many people accept the default 1000mb on the inspiration.. __________________ 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.
(Online)

25th April 2005, 22:52	#27 (permalink)
*EBT* Apprentice Luddite Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Feb 2005 Location: UK, Brighton Posts: 1,969	Diminishing returns Joe..... its uses a lot of O2 to hard flush the loop much above about 1.55. I dont deny what you're saying, I just dont think that 0.05 is worth blowing through shedloads (its a new SI unit) of O2 for. __________________ Eagles May Soar, but weasels don't get sucked into jet engines! Rebreather World Terms of service Real diving t-shirts for real divers
(Offline)

25th April 2005, 23:35	#28 (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: 3,001	Quote: (Originally Posted by wreckweasel) Diminishing returns Joe..... its uses a lot of O2 to hard flush the loop much above about 1.55. I dont deny what you're saying, I just dont think that 0.05 is worth blowing through shedloads (its a new SI unit) of O2 for. I think its a matter of technique.. I can easily get 1.6 (Ob RBS with OTS counterlungs)without using lots of oxygen, (I want my students to be able to get above 1.5 without much effort)... This is the way that I do it... 1)inhale as much as I can 2) crush the bags, 3)exhale out of loop as much as I can.. 4) Hold the o2 manual in 5) take a deep breath exhale out through the nose 6) take several shorter breathes on the loop to push the gas around the loop 7) vent through OPV and nose as needed This takes alot less gas than 4 or 5 deep inhales/exhales.. WIth the bags crushed it takes very little gas in the loop.. The actual dead space in this way (on an inspiration - will vary on other RBS) is only about 2l of gas times 1.6 atas.. If you don't crush the bags it takes LOTS of gas.. I don't know the flushing technique that you wer taught, but when done correctly (and if you have access to the counterlungs) you really can eliminate the counterlungs, and the only volume you are flushing is your lungs, the dead space in the cannister, dsv and hoses. The most likely reason I am efficient at flushing it is I have lot of practice.. to get a good calibrate on the HH I must have 100% oxygen in the loop... But I agree 1.55 is fine.. I am a hardass in traing just because I want them to perfect their technique. Joe . __________________ 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.
(Online)

25th April 2005, 23:41	#29 (permalink)
AM In love with the big blue Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Earth. Posts: 618	I see both sides here. In fairness it is easy on the Inspiration to reach 1.6. When you dump gas overboard on Inspiration or ascend, the controller will automatically help you by firing even when you are flushing. It is slightly more difficult on the KISS. The flow rate and manual over ride on the KISS definitely have a slower gas injection rate. You put a KISS and Inspo together on a shelf, take them to .70 and try to raise PPO2 using respective manual injection and Inspo restrictor - you will see the tangible difference. Regards AnneMarie PS 1.6 is a good test to do at 6m always to verify the linearity of the sensors. __________________ Attitude keeps you alive
(Offline)

26th April 2005, 00:20	#30 (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: 3,001	Quote: (Originally Posted by AnneMarie) I see both sides here. In fairness it is easy on the Inspiration to reach 1.6. When you dump gas overboard on Inspiration or ascend, the controller will automatically help you by firing even when you are flushing. It is slightly more difficult on the KISS. The flow rate and manual over ride on the KISS definitely have a slower gas injection rate. You put a KISS and Inspo together on a shelf, take them to .70 and try to raise PPO2 using respective manual injection and Inspo restrictor - you will see the tangible difference. Regards AnneMarie PS 1.6 is a good test to do at 6m always to verify the linearity of the sensors. I originally didn't realize he was diving a classic KISS.. Definately no way to eliminate the counterlungs.... He stuck sucking the loop like a Hoover.... I would say a 1.55 is pretty damn good in this case... __________________ 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.
(Online)

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